Diet and Perception

This 2016 article explores the impact of the increasing exposure in society to images of desirable foods (what is often labelled 'food porn', or 'gastroporn') via digital interfaces might have, and whether it may inadvertently be exacerbating our desire for food (what we call 'visual hunger'). Here Spence et. al (2016) review the evidence for the potential profound effect viewing these images may have on neural activity, physiological and psychological responses and visual attention (especially in the ‘hungry’ brain). It is explained that the blame is often put on the global food companies for offering addictive foods, designed to use just the right amount of pleasurable ingredients such as sugar, salt, fat to hit the “bliss point” and for making these calorie-rich foods so accessible. The review aimed to find out if there are other implicit cues in our environments that might be triggering hunger more often than it is good for human well-being.

Park et al. (2020) experimented on 30 individuals with type 2 diabetes (where the body doesn’t utilise insulin) to test whether cognition can affect plasma glucose levels. All the participants were given a beverage with the same ingredients but the drink was labelled with deceptive nutritional information. The subjects’ sugar levels in the blood were then measured four times before and following beverage consumption. It was revealed that when the participants believed that the drink contained large amounts of sugar as written on the labels, their blood sugar levels were elevated. The authors add that individual eating behaviors and nutritional satisfaction are connected to the sugar concentration in their bloodstream. These results support the concept that the body can anticipate sugar intake and react by regulating its metabolism. The implications of this study are that psychological intervention programs could play an influential role in diabetes management, even beyond the current programs that involve controlling diet, exercise and medications.

Sütterlin and Siegrist (2015) set up 4 experiments to find out whether people use simple heuristics to assess the healthiness of food products since for example the inclusion of the word “fruit” in “fruit sugar”, the colloquial name for fructose in Germany could mislead one to perceive the product as relatively healthy due to the association between fruit and health. Experiment 1 involved providing 164 individuals with one of two cereal bars, with one group given the nutrition table with the label “fruit sugar” and the other group provided with that labeled solely “sugar”. The results pointed to the participants holding a more positive perception of the “fruit sugar” cereal than the bars excluding the word “fruit”. Experiment 2 was a within-subjects designed version of Experiment 1, with all 202 subjects evaluating both cereal bars simultaneously, which resulted in the same trend occurring. Experiment 3 (N = 251) ruled out the alternative explanation that the effect could be due to differing inferences about the product's ingredients based on the label used, that is, that the product labeled with "fruit sugar" contains fruit. Results from the 4th experiment involving 162 participants indicated the labeling of the word “sugar” and its healthiness association mediated the previously observed effect. This study clarifies that symbolic information on food products can influence people’s perception of its healthiness, which can prove valuable from a marketing and public health standpoint.

Exploring different strategies on promoting the implementation of healthier diets, this study examined the perceptions and definitions of eating pleasures and healthy eating in a population from Quebec City, Canada. There were 12 focus groups formed, including men and women of normal weight and obese. The objective was to identify commonalities and differences between the participants’ perceptions and definitions and comparing the data based on sex and body mass index (BMI). The salient perceptions were similar among subgroups based on sex and BMI. In most cases eating pleasure was defined through food characteristics related to sensory qualities and psychosocial contexts whereas the definitions of healthy eating were mostly found to mention food characteristics related to nutritional quality and ways to regulate eating behavior. To conclude, the Quebecers’ concepts of eating pleasure and healthy eating were dissimilar but could be seen as compatible and suggests the use of eating pleasure could provide a promising way to promote healthy eating.

This review seeks to find the impact of cognitive features on the perceived healthiness of foods and the resulting influence on overall food choices and consumption. It is suggested the inclusion of nutritional information on products in the form of labels and claims, which was integrated as a strategy to promote healthy diet consumption, could be misinterpreted by the consumers. The findings of this review imply cognitive factors (including type of food and branding) may not consistently or systematically affect food choice and intake but significantly contributes to judgmental bias and can influence the person’s perception of healthiness.

A sample US subpopulation (281 adult parents) undertook this 2019 study investigating the influence of plate size on a person’s perceptions and recall of food and meal size. The parents drew and labeled the foods they expected to eat that night, drawing on either a 23cm or 28cm paper plate. There were apparent differences in food sizes drawn between the two plate sizes as well as between the sexes. Around 24% more food was drawn on the larger plates than the small plates. This trend was seen in both sexes, although men drew 37% larger food sizes on the 28cm plates than on the 23cm plates, and women had their portions 17% larger on the bigger plates. 60% of the overall differences in food size between plates was observed when the biggest food was drawn. Furthermore, bigger meat portions were drawn by both men and women on the 28cm plates. These results provide evidence of the influential role of plate size on these adults’ estimates of plate size, with the observed effect more substantial in men than women which could result in greater food consumption in men, especially meat products.

Harray et. al (2017) compared the perceived and actual intakes of energy-rich nutrient-poor ‘junk food’ (JF) and sugar-sweetened beverages (SSB) in young adults in Perth of Australia, by assessing before-and-after eating images of the standardised portions (143kcal) of JF and SSB. Amongst the adult participants (aged 18-30), mean consumption of JF+SSB was 3.7 (2.0) servings per day. The women who thought about drinking less SSB were found to consume more servings per day (1.5 (1.2)) than men who thought about drinking less (0.7 (0.5)). On the other hand, men who planned to cut down on JF ate more servings/day (4.6 (2.4)) than women who wanted to reduce JF intake (2.5 (0.7) servings). Those who consumed the least JF and SSB were individuals who paid a lot of attention to include healthy choices into their diet, who consumed significantly less than those who took only a bit of notice, were not thinking much about it and those who didn’t consider health at all in their food intake. These results suggest perceptions and attitudes regarding JF and SSB can be associated with level of consumption. Since those individuals who did not consider cutting down on these foods consumed larger amounts, they appear to be an important target group for promoting healthy eating.

This 2017 comparative study involving 570 people from Canada, China, Korea and New Zealand investigated the cultural influences on perception of food portions as a function of plate size. Previous research had suggested manipulations of plate size can directly affect perception of food intake but this present study claimed to be the first to examine differences in results between various countries and cultures. Photographs of ten culturally diverse dishes were presented on 27cm (large) and 23cm (small) plates before the participants rated estimated usual intake and expected fullness after the meal. After controlling for individual BMI, liking and familiarity of the presented food, the analysis revealed clear differences between cultures: in Chinese and Korean respondents plate size did not have an effect on expected fullness or estimated intake whereas the size manipulation significantly impacted upon Canadians and New Zealanders; participants from Canada and New Zealand also reported significantly higher estimated intake ratings than Chinese and Koreans, although estimated fullness ratings were found to be comparable or higher than from the Asian subjects. These results suggest from a cultural perspective that estimated fullness and consumption are learned through dining experiences and highlight the importance of considering eating environments and contexts when assessing individual behaviours relating to dietary consumption.

Since there is evidence indicating the potential approach oriented towards eating pleasure to promote the consumption of healthy foods, Vaillancourt et. al (2019) compared perceptions and the potential effect of pleasure-oriented as well as health-oriented messages on promoting healthy eating among French-Canadians. Perceived message orientation and effectiveness, perceptions towards healthy eating as well as emotions, attitude towards healthy eating, and intention to eat healthily were evaluated. The study population - consisting of 100 adults with an average age of 45.1, 50:50 male to female ratio - were randomly assigned to read one of the two leaflets with the messages, before completing questionnaires online and also reporting their experiences in a visit to the Institute of Nutrition and Functional Foods. Both pleasure and health messages significantly improved global attitude towards healthy eating while perceived message effectiveness and induced emotions in response to reading were similar between the two leaflets. The pleasure-oriented message was successful in inducing the perception that eating healthy can be pleasurable, with additional analyses also revealing the pleasure leaflet increased affective attitude towards healthy eating to a greater extent than the health leaflet. The health message appeared to improve cognitive attitude more than the pleasure leaflet however. The researchers conclude that the leaflets may be appropriate to promote healthy eating through health- and pleasure-related approaches.

Jezewska-Zychowicz and Guzek (2017) conducted a survey involving 344 consumers aged 20-65 years old to investigate whether dieting, perception of body weight, diet and preparing meals are linked to particular dietary patterns based on survey responses, and also to identify eating patterns based on declared food consumption rates (measured using a 7-point scale). Cluster analysis was used to identify three dietary patterns of behaviour: ‘potentially beneficial to health’, ‘potentially unfavourable for health; deficient’ and ‘potentially unfavourable for health; excessive’. Significantly more participants were of normal body weight, was dieting at that moment or had in the past, evaluated their diet as very good or good, prepared their meals at home and showed “potentially beneficial for health” behavior, all in comparison to other groups. Variations in responses to meal preparation were seen in the “unfavorable for health” dietary pattern, while less meals were prepared at home by those belonging to the “deficient” pattern. Finally, the writers claim that the pattern of potentially beneficial dietary habits correlated to weight control through a slimming diet and greater involvement in the meal preparation and that food choice skills need to be developed when educating people on nutrition.

In this qualitative study published in 2018 16 key informant interviews were conducted and eight focus group discussions took place in northern Ethiopia in order to find out people’s perception of a ‘healthy’ diet in this African country and the barriers to practice this idea of a ‘healthy’ diet. The Ethiopians’ practice was mostly consistent with their perception, while they sometimes acted contrary to the perception because of personal preference and physical or financial obstacles. People were often unconcerned by the health implications of their habitual dietary practice, such as drinking a lot of sweet coffee. This study investigated and has shown the dynamics between perception and practice of ‘healthy’ diets among people in northern Ethiopia with the aim of removing any obstacles to a beneficial diet and raising awareness in the country of non-communicable diseases (NCDs) such as cardiovascular disease and diabetes, which are increasing with regards to burden in these low-income countries.

Turnwald et. al (2019) tested whether taste-focused labels can attract higher vegetable intake compared with health-focused labels at five university dining halls across the United States. Across 137,842 diner decisions, 185 days, and 24 vegetable types, taste-focused labels increased vegetable selection by 29% and overall vegetable consumption as well compared with health-focused labels and by 14% compared with basic labels. In addition, taste-focused labels outperformed labels that merely contained positive words, fancy words, or lists of ingredients. As additional studies further inspected the mediators, moderators, and boundaries of these effects, it was discovered that increased expectation of a positive taste experience mediated the effect of taste-focused labels on vegetable selection, and moderation tests revealed greater effects in settings where tastier vegetable recipes are served. This research paper indicates that emphasising tasty and enjoyable attributes increases vegetable intake in real-world settings.

This 2015 study conducted focus groups with Brazilian university students to find out their perceptions of the concept of calories, how it relates to food healthiness, and the role of calorie information on menus in influencing food choices in different restaurant settings. Among the 21 undergraduate students who took part in this cohort, calories were understood to be energy units and their excessive intake was associated with weight/fat gain. However, food healthiness was not associated with calorie content, but rather with food composition as a whole. Calorie information on restaurant menus was not considered enough to influence food choice, with only some participants also using calorie information on menus to control food intake or body weight. The discussions between the students suggested their comprehension of healthy eating is a more complex issue than calorie counting, and they would need more information on nutrition, not only about calorie content, in order to influence food choices in restaurants.

Since food cues affect hunger and nutritional choices, the objective of the first study was to explore the impact of food cues on appetite-related hormones and to examine the functionality of the secreted hormones on macronutrient uptake in a healthy subpopulation. The healthy, non-obese participants were presented with random non-food pictures on the first day and then were shown food pictures on the second day. A second study was focused on confirming response differences of total and active ghrelin to stimulation with food pictures and to a meal followed by the stimulation. Duszka et. al (2020) also planned to identify factors contributing to response to food cues. In this second study the subjects were asked to drink a milkshake following the picture session and their levels of blood glucose, triglycerides and hunger-related hormones were taken. The concentration of several hormones measured in the blood were found to be interdependent, while in the case of ghrelin and gastric inhibitory peptide (GIP) as well as ghrelin and glucagon-like peptide-1 (GLP-1), this co-occurrence relies on the visual cues. Regulation of total ghrelin concentration following food stimulation is also highly individual and responders showed upregulated total ghrelin, while the concentration of active ghrelin decreased following a meal. Interestingly, there was a correlation identified between lower protein content and lesser colour intensity of food pictures with higher participants’ ratings of the pictures. After gathering all this data, it was concluded that observation of food pictures influences the levels of several appetite-related hormones, and the close link of visual cues to physiological responses may be of clinical relevance.

With the aim of improving the effectiveness of nutrition education programs and behavior change campaigns, Pettigrew, Talati and Pratt (2017) studied 409 Australian survey respondents aged 25-64 years on their perceptions of the meaning of four terms used to describe unhealthy foods: junk food, snack food, party food and discretionary food. The research found ‘junk food’ to be the term most aligned with unhealthiness, and likely to represent wording that is relevant to many target audience members. Other findings included the term “discretionary food” was not a familiar term for many respondents, and snack foods were considered to include both healthy and unhealthy food products. Both snack foods and party foods were often described as being consumed in small portions. These results highlighted that different terms for unhealthy foods can have substantially varying meanings for audience members and therefore, a detailed understanding of these meanings is required to ensure that nutrition guidance and health promotion campaigns use appropriate terminology.

The main objective of this 2012 Korean study was to determine whether self-perception of diet quality is connected to personality, impulsiveness, stress, coping strategy, sense of coherence, self-efficacy and social support. This cross-sectional study gathered data by conducting 15-minute face-to-face interviews with 1530 South Korean volunteers (aged 30-69) without a history of cancer. Respondents were more likely to perceive that they consumed a healthy diet if they were older than 50 years, lived with a partner, had a monthly family income greater than $4,000 USD, had a low perceived risk of cancer, consumed less alcohol, exercised regularly, had a less agreeable or conscientious personality, had low stress levels, had a high sense of coherence or self-efficacy, and had ample social support. These results associating psychosocial factors, such as personality, stress, sense of coherence, self-efficacy and social support with self-perception of diet quality can be used and analysed further to assist with the design of educational campaigns.

König & Renner (2019) conducted three studies with intervention strategies for boosting healthy food choice by prompting consumers to eat a colourful lunch at the appropriate moment. Effectivity and feasibility of this intervention strategy were tested in two laboratory experiments and one real-life, smartphone-based Ecological Momentary Intervention. The first study with 83 participants involved 4 meals (colourful, typical, healthy and low-calorie), the second with 42 subjects and tested 3 meals (colourful, typical and varied) from a Fake Food Buffet, and in study 3, 80 participants recorded images of 1,210 lunch meals over a period of 3 weeks using mobile visual food recording. All participants were asked to rate the prompts’ feasibility and in the second week, received a daily smartphone prompt to eat a colourful lunch. Results showed that prompting the sample to eat colourful foods increased the proportion of healthy foods consumed compared to typical meals in all three studies, with the individuals taking part in the study reporting that the prompt was easy to follow and act upon. In studies 1 and 2, colourful meals contained more fruit and vegetables, while in study 3 the prompt increased vegetable consumption. The colourful meals were said to be the tastiest in study one. This study suggests it may be promising to prompt people to eat colourful meals to encourage healthy food choices in daily life.

While there is evidence that customers are influenced by the ambient scents in retail stores and restaurants, Singh et al. (2019) wanted to discover the impact of the restaurant waiting staff’s scent on customer perception and behavior, specifically on menu choice, flavor perception, overall liking of meal items, meal satisfaction, amount consumed, and tip amount for wait staff. The 213 participants with no problems smelling were chosen to sit in a mock restaurant and order one of four chicken meat menu items (baked, broiled, fried, and smoked chicken) while being served by wait staff wearing aprons applied with one of three scents: congruent (smoky barbecue scent); fragrance (perfume scent); and no scent (control). While menu choice and flavor perception of the meals were not affected by the waiters’ scents, the overall liking of food items, meal satisfaction, and amount of tip given to the staff did vary depending on the gender of the customer. Female clients gave higher ratings of overall liking and meal satisfaction in the presence of the fragrant scent compared to no scent, whereas no impact was observed in male customers. Moreover, under the congruent scent condition consumption of chicken meat items was lowest. This study provides proof that the scents of restaurant wait staff can modify diners’ experiences and behaviors, and that these influences vary according to gender of the customer.

While energy-containing drinks are said to have a minor effect on satiety (sensation of feeling full), McCrickerd et al. (2014) assessed whether the context in which lower- (LE, 75 kcal) and higher-energy (HE, 272 kcal) beverages are consumed can influence the level of satiety it induces. The two beverages were consumed by 80 participants over two test days in one of four contexts: 20 individuals drank the thin version of the test-drink as a thirst-quencher; another 20 people consumed the beverage as a filling snack; 20 more participants drank the beverage after being given no additional information; and a fourth group of 20 received subtly thicker versions of the beverages without additional information. The amount of food eaten at lunch one hour later depended on the beverage context and energy content (p = 0.03). No significant differences in consumption were found between the higher- and lower- energy drinks in the participants who were not given additional information and in the individuals who perceived the drinks as just thirst-quenchers. But when the beverage was consumed as a filling snack, the subjects ate less at lunch after the HE beverage compared to the LE version. This effect was also observed among those who drank subtly thicker beverages - food consumption was lower after the higher-energy test-drink. These findings provide evidence that beverage intake can affect the impact of its nutrients on appetite regulation and that a beverage's sensory characteristics can limit its satiating power.

This 2016 study investigated the influence that the sensory characteristics and nutrient constituents of drinks have on its satiating effect. The 23 healthy volunteers were given one of four different beverages varying in both overt sensory qualities and covert energy content: thin, low sensory (LS) combined with low energy (LE); thicker, creamier, enhanced sensory (ES) and low energy (LE); low sensory (LS) and high energy (HE); and enhanced sensory (ES) with high energy (HE) content. The participants were then asked to rate their appetite levels, and were given unrestricted access to food. Blood samples were also taken to monitor their plasma concentrations of glucose, insulin, pancreatic polypeptide (PP) and cholesystokinin (CCK) over 90 minutes and throughout their lunch. Hunger was suppressed the most among volunteers who consumed the thicker, creamier, higher sensory drink with high total energy, resulting in lower food intake too. Yeomans et al. (2016) also found that insulin levels rose higher after high-energy drinks than low-energy, and following intake of thicker and more creamy beverages compared to thin. Moreover, pancreatic polypeptide levels were higher after the enhanced sensory drinks too, compared to thin, low-sensory beverages. Cholesystokinin concentrations only increased after consumption of thicker beverages with high energy content. This study demonstrates that the manipulation of a drink’s nutrient components and sensory elements can affect satiety levels.

While slow and prolonged food consumption is believed to make you feel more full, this 2018 review assessed the impact of oral processing characteristics (for example chewing and lubrication) on food intake and measures of appetite such as hunger and desire to eat. The systematic literature search on 6 different databases yielded 38 papers (detailing 40 unique studies with 70 subgroups), which were used for meta-analysis. Raw data on food intake was seen 65 times, hunger 22 times, and desire to eat ratings 15 times. Oral processing parameters such as number of chews, eating rate and texture manipulation seemed to substantially affect food consumption and appetite ratings to a lesser extent. Meta-analysis also indicated that aspects of oral processing related to chewing elicited a significant effect on self-reported hunger and food intake. Krop et al. (2020) insist that future research should confirm the role of oral processing including chewing and lubrication in promoting satiety, especially since few studies have reported the impact of lubrication on appetite.

Bray & Carek (2020) presents the gene that is partly involved in the genetic processes crucial in determining a person’s sensitivity to bitter tastes - TAS2R3. The review explains how this gene affects dietary habits, and discusses the strategies employed to persuade people to include more fruits and vegetables in their diets. The authors believe that physicians could develop ideal personalized nutritional plans for individuals using their TAS2R3 genotype.

While food preferences and dietary habits are heavily influenced by taste perception, Chamoun et al. (2018) point out that characterization of taste preferences based on genetic variation is rising. Taste biology and genetics may lead the way to novel strategies and thereby the reduction/prevention of chronic diseases. This review focuses on single nucleotide polymorphisms (SNPs), which are specific genetic variations that, if occur in taste receptors, have been associated with the way in which fat, sweet, bitter, umami, and salt tastes are experienced. Also discussed are how these SNPs contribute to food preferences and chronic disease/health. The authors highlight the growing evidence that suggests that the role of genetics in taste perception may be more important and influential in children than adults due to the significant differences in cultural knowledge and awareness.

The purpose of this 2017 study was to evaluate the relationship between four different psychophysical measurements of sweet taste perception (detection and recognition thresholds, sweet taste intensity and hedonic liking of suprathreshold concentrations) using glucose as the tastant (substance that stimulates the sensation of taste). Another aim was to discover a measure that associates with sweet food consumption. The participants (44 women aged between 20-40 years) completed a four-day food record and 2 types of questionnaires - a sweet food-food frequency questionnaire and a sweet beverage liking questionnaire. Although no correlations were found involving glucose detection and recognition thresholds, sweet taste intensity was negatively associated with total energy and carbohydrate intake, frequency of sweet food consumption and sweet beverage liking. A positive link was also apparent between sweet hedonic liking and total energy and carbohydrate intake.

Tan & Tucker (2019) conducted a systematic review of studies examining the relationship between taste function/perception and dietary consumption, in order to find the measure of taste most closely associated with dietary intake in healthy adults. Studies were grouped into 3 categories: those that assessed taste sensitivity; taste intensity; and hedonic (pleasure-related) responses to sweet stimuli. While there was little evidence linking sensitivity and intensity with dietary intake measures, hedonic studies were more likely to show associations with dietary consumption, particularly when analyzing participants who like sweetness separately from those who dislike sweet foods. However, the heterogeneity (diversity) among the dietary measures and stimulus concentration of these studies, as well as the small sample sizes, likely made it difficult to determine consistent relationships between the variables.

Since people who stick to low-sodium diets eventually develop a preference for less salt over time, Wise et al. (2016) wanted to find out if sweet taste perception is altered by reduced sugar consumption. The purpose of this study was to discover whether the sweetness intensity and pleasantness of sweet foods and drinks can be influenced by reducing the dietary intake of simple sugars. The participants, who were aged between 21-54, were split up into 2 groups after the baseline month: one group was randomly selected to eat a low-sugar diet for the next 3 months, with instructions to replace 40% of calories from simple sugars with fats, proteins, and complex carbohydrates; and the other control group were not asked to change their sugar intake. The subjects in these 2 groups were matched for demographic characteristics, body mass index, and intake of simple sugars before being assigned to each group. Each month each participant rated sweetness intensity and pleasantness of vanilla puddings and raspberry beverages that varied in sugar levels. During the final month the remaining participants were allowed to choose any diet they desired. The results demonstrated no difference between the two groups in sweetness ratings during the baseline or first diet month. It was during the 2nd diet month that the low-sugar diet group reported higher sweetness intensity than the control group, when eating the low-sucrose puddings. During the third diet month also, the participants who were instructed to lower their sugar consumption rated both low- and high- sucrose containing pudding samples as ∼40% sweeter than the control group did. The researchers identified weaker effects on sweetness ratings regarding the sweet beverages, and could not find any significant variation in pleasantness ratings. Overall, this experiment suggests that sweet taste intensity can be modulated by altering simple sugar consumption.

Low et al. (2014) explain that taste may play an important role in influencing food acceptance and/or energy intake since a person’s ability to detect or sense sweetness in the oral cavity is thought to be one of many factors involved in determining food acceptance. In addition, evidence is emerging suggesting that the signaling mechanisms related to sweet tasting may be working in the gastrointestinal system as well as in the oral cavity. To explain the excess energy intake thought to be substantially contributing to the growing global rate of obesity, a better understanding of the sweet taste system’s role is essential, not to mention greater knowledge on the individual variation in detecting sweetness in both the oral and gastrointestinal system. This review summarizes data potentially linking the sweet taste mechanisms within the oral cavity, gastrointestinal tract and the brain systems (activated by caloric sugar, high intensity sweeteners and sweet tastes) with satiation (sensation of feeling full) and thereby perhaps with BMI and obesity.

In this review, McCrickerd & Forde (2016) focus on sensory characteristics and how we can utilize it to reduce people’s food/energy consumption. The regulation of intake can largely depend on the sensory processes at work while eating, particularly the hedonic/pleasure-related response to specific sensory cues. The authors note that the sensory experience begins before consumption, and continues until even after the meal. Also discussed: how taste and texture affects meal size and the level of post-meal fullness; and the role of visual and odour cues in finding food nearby, including its impact on subsequent food choice. This area of research, in sensory nutritional science, will need to look into how these principles affect weight management. To improve food intake control, a form of sensory manipulation will need to be identified and combined with a drop in palatable food consumption.

Spence (2014) explains how the sounds that you hear when consuming foods and drinks are critical to your experience and enjoyment. This can be the sound made by chewing and biting, while the texture of the food may also be important. Just listen to those crispy, crunchy and crackling noises. It is the synchronization of such eating sounds with the act of feeding that can alter the consumer’s experience of what they think they are eating, according to a rising number of studies.

The aim of this 2018 study was to find out the extent to which patients’ treatment-related expectations influence their appetite. Ninety healthy participants of normal weight were randomly selected to one of three groups: appetite-enhancing placebo group (given placebo capsule suggested to be appetite-enhancing); a satiety-enhancing placebo group (received placebo said to increase feelings of fullness); or the control group (administered placebo thought to have no effect on appetite). The subjects’ level of hunger/satiety were recorded as ratings, which were taken before the group allocation and for the following 2 hours. Blood samples were also repeatedly taken to analyze and compare the participants’ plasma ghrelin concentrations (used as a marker of hunger). There was a significant reduction in appetite and increase in feelings of satiety induced by the satiety-enhancing placebo intervention, compared to the control group. Whereas, hunger levels were not affected by the placebo capsule said to be appetite-promoting, although plasma ghrelin levels were elevated among the female recipients. Hoffman et al. (2018) have uncovered the impact of expectation on appetite-regulating intervention effects. The data indicated that these appetite-regulating placebo interventions can elicit a psychobiological response.

Food texture influences on satiety: systematic review and meta-analysis

Factors that influence the perceived healthiness of food—review

Taste perception and food Choices

Yin et al. (2017) investigated the impacts of aroma and taste, on its own and as a combination, on appetite sensation and on subsequent food consumption. In this study, 26 female participants (24 ± 4 years, 20.9 ± 1.9 kg⋅m−2) were given 15 minutes to drink either water (S2, 0 kcal), water with strawberry aroma (S2, 0 kcal), water with sucrose and citric acid (S3, 48 kcal), or water with strawberry aroma, sucrose and citric acid (S4, 48 kcal), before receiving unrestricted access to a pasta meal after 65 minutes. The groups S1 (water), S2 (aroma) and S3 (taste) did not differ in appetite sensation, while the S4 drink (aroma + taste) was found to suppress the feeling of hunger over the 15 minute drinking period. Sample 4 induced satiety more than S1 at 5, 20 and 30 minutes after the drink was consumed (p < 0.05), more than S2 (aroma) at 5 and 20 min post-drink consumption (p < 0.05), and more than S3 (taste) at 5 min post-consumption (p < 0.05). S4 (aroma + taste) was also reported to be the strongest perceived flavour. However, pasta energy intake did not vary between the 4 drink conditions. The results suggest that the combination of aroma and taste caused greater satiation and short-term satiety than water and aroma or taste on its own. Possible explanations proposed include the greater perceived flavour intensity or higher perceived flavour quality and complexity of the aroma-taste mixture.

Since food appearance, particularly its colour, influences flavor perception, this 2020 study utilized the power of virtual-reality (VR) technology to assess whether changing the milkiness of coffee through VR can affect perceived flavor and liking. Thirty-two UK consumers were given four samples of black cold brew coffee at 4% and 8% sugar concentration while wearing VR headsets and viewing coffee manipulated to look a dark brown or light brown colour. Each participant tasted each sweetness and color combination before rating the sweetness, creaminess, and liking for each beverage sample. The results showed that drink color did not have an impact on the subjects’ perceived sweetness or liking. However, perceived creaminess was found to be significantly altered by the color of the drink. The light brown coffee was rated to be creamier than the dark brown sample. Overall, the researchers recommend the utilization of VR in the examination of food perception. A future prospect with potential for VR would be promoting healthy dietary behaviors through food appearance manipulation.

Endocrine cephalic phase responses to food cues: a systematic review. Advances in nutrition (Bethesda, Md.). 11. 10.1093 Lasschuijt et al. (2020) conducted this review to determine the magnitude and onset time of cephalic phase responses among humans. Cephalic phase responses (CPRs) are conditioned anticipatory physiological responses to food cues that start before the absorption of any nutrients. Five scientific databases were scoured for studies that measured cephalic, hormone, or endocrine responses using insulin or pancreatic polypeptide (PP) levels. Fifty research articles were included in the meta-analysis, which indicated notable elevations in insulin and pancreatic polypeptide concentrations in 41% and 48% of the treatments, respectively. The median insulin increase was 2.5μIU/mL (30% above baseline) at 5± 3 min after food cue onset, while the median PP increase was 99pg/mL (68% above baseline) at 9± 4 min after food cue onset. These figures were small compared with spontaneous fluctuations. There was also a high level of variation in magnitude and onset time, failing to suggest any links between cephalic phase responses with satiation and glucose homeostasis that were hypothesized.

While hedonic pleasure has been linked with brain function in the past, Berridge & Kringelbach (2011) explore new insights into how brains contribute to the hedonic aspect of sustained or frequent pleasure. Well-being and happiness have been reported to require both positive affect or pleasure (hedonia) and a sense of meaningfulness or engagement in life. This article also discusses how the brain might connect these two to form states of positive well-being. There has been recent advancements in the understanding of hedonic processing due to the largely similar hedonic brain mechanisms seen in humans and other mammals. It has been reported that the brain mechanisms of higher abstract pleasures strongly overlap with more basic sensory pleasures. Thus, the strategy of Berridge & Kringelbach acknowledges this new evidence as well as the findings on brain mediators that produce the pleasure of sensations.

This 2013 article by Berridge & Kringelbach marks the progress seen in the understanding of pleasure or positive affect (hedonia) and the process of wanting, liking, and learning. The authors also note the lack of knowledge accumulated so far on how one feels a meaningfulness or engagement in life, otherwise known as eudaimonia. The hedonic brain mechanisms shared between humans and other mammals have helped better understand hedonia. Evidence has grown to show strong overlaps between the brain networks of higher pleasures with those more basic sensory, suggesting an opening insight into the underlying brain circuitry that is responsible for all pleasures. Pleasure is vital in leading humans to make survival-related decisions on resource allocation on brain processes. A careful balance may be required to experience positive well-being rather than the maximum prioritization of one sole process. In this way, the successful balancing of the wanting and liking processes may be the crucial link between hedonia states with eudaimonia, leading to the balanced states of positive well-being that come immediately before happiness.

While the senses taste and smell play an influential role in the choice and intake of food, this 2017 article discusses the differences in functions of smell and taste on dietary behavior. Boesveldt & de Graaf explain that sensing an odor leads to greater appetite for the cued food but its impact on food choice and consumption is a little less clear - perhaps involving other factors such as awareness or intensity of the odors, and the personality traits of the person. On the other hand, the role of taste is better understood. In addition to texture, taste is responsible for determining the rate of food intake, the exposure duration of food in the mouth, and thus level of satiation. By applying these findings to real-life situations, the longer-term impacts of taste and smell on energy consumption can be analyzed. And in doing this, hopefully people’s eating behaviors can be modified to move towards a less obesogenic society.

While food texture is a major influencer of an individual’s perceived satiation and the amount of food they would consume, Cahayadi et al. (2020) decided to test its effects on snack intake. In this crossover trial, the 74 participants (31 females and 43 males) were given permission to eat as little or as much as possible of two potato chip types. The chips were similar in hedonic value but clearly distinguishable by texture. The results revealed a significant difference in perceived satiation between the two chip types but the level of consumption was not affected across the whole sample size. While analyzing the male subjects, however, the satiation levels reported were higher for the chips treated with pulsed electric fields (PEF) technology than the untreated control chips. These data suggest that modifying the texture of food can help reduce energy consumption through snacks. Moreover, this study highlights the importance of considering gender effects in research studies involving dietary behaviors.

In this 1998 study designed to assess how oral, gastric, and intestinal factors contribute to appetite control, 425ml of tomato soup was administered to nine healthy, fasted, male volunteers in various forms. Soup was given orally, through the stomach intubation (intragastrically - covertly and overtly), and through the duodenum (intraduodenal - overtly). The subjects rated their levels of fullness, hunger, and desire to eat over a 2-hour period, while the rate of gastric emptying was also measured after oral and intragastric soup intake. After soup was infused into the small intestine at a rate in line with normal gastric emptying, there was no significant impact on hunger, desire to eat, or fullness ratings. Also, there was no variation in gastric emptying between covert and overt intragastric soup infusions, but the researchers highlighted a suppression of appetite following covert intragastric administration that was also heightened when participants were informed of the route of infusion. Between all conditions, oral consumption resulted in the greatest appetite inhibition, and produced a slower rate of gastric emptying compared with both methods of intragastric soup infusions. Cecil et al. also reported strong associations between appetite ratings and both gastric and intestinal contents following intragastric soup intake, and these were found to be stronger after oral soup consumption. It was clear that orosensory, gastric and intestinal factors can interact to produce optimal expression of fullness and hunger suppression.

Dai et al. (2020) planned to determine the role of visual attention in healthy eating intentions and choices since it was not yet fully understood how people decide what to eat. Two-alternative forced choice tests were conducted to make participants choose 2 pairs of healthy and unhealthy foods, varying in taste preference. The researchers modified the salience of these food items, as well as the cognitive load and time pressure (to test the generalizability of the salience effect). The manipulation of salience had a great effect on all situations, even in instances where the alternative was an unhealthy, tasty food. It was noted that healthy foods were chosen more often when salient. In addition, when these healthy options were selected, subjects were more likely to choose something healthy again in the next trial. The impacts of salience were also robust when high cognitive load and time pressure were applied. Hopefully, these results help inform interventions designed to promote healthy eating.

This 2016 article emphasizes the influences of various food properties on several outcomes. Food form in particular can impact nutritional outcomes through multiple mechanisms involving cognitive and oral sensory processes, and stomach and intestine activity. Dhillon et al. explain that holding expectations about the form of food can determine digestive processes, metabolism occurring after absorption, the sensory ratings of the food product, and the level of fullness one feels. Moreover, mastication depends on the structure of food, which can alter appetite, energy, and the nutrient bioavailability in the digestive tract. Finally, the physical form of food particles can affect absorption of nutrients, the speed at which the stomach is able to empty its contents, and the time it takes for the food to pass through the intestine also. Thus, there are significant implications involving food form in ingestive behavior and health outcomes.

According to Duerland et al. (2019), the sensations felt after ingesting food can paint a clear picture of the overall eating experience. The objective of this study was to determine the dynamics of different post-ingestive sensations following food consumption, and to assess the impacts of protein and carbohydrates on post-ingestive and hedonic (pleasant/unpleasant) responses. This trial was of a randomized, crossover design, involving the intake of breakfast, one high in protein (named HighPRO) and one rich in carbohydrates (HighCHO), on two separate days. The post-ingestive sensations of the 48 participants were measured every 30 minutes for 3 hours following breakfast consumption. The main effect of time was found to be significant for all sensations post-ingestion. Also, high-carbohydrate breakfast induced greater hedonic responses and higher ratings for satisfaction, food joy, overall well-being and fullness, compared to the high-protein breakfast. On the other hand, the HighPRO meal was rated higher for sweet desire following consumption. These findings suggest that the sensations that arise post-meal may play an important role in the subsequent food choice of consumers and especially in the intake of extra calories.

Since food assessment varies across cultures, Duerland et al. (2020) conducted a study to compare the sensations experienced following food ingestion by participants in China (n=53) and those in Denmark (n=48). The main objective was to discover the drivers of post-ingestive food pleasure (PIFP) among both sets of subjects. Both post-ingestion sensations and PIFP were measured for 3 hours following breakfast consumption. Importantly, perceived satisfaction, in addition to physical, mental, and overall well-being were highly impactful on PIFP in both countries. However, there were differences between the two groups of subjects. Unlike the Chinese, the Danish consumers perceived sensations such as satiety, hunger, desire to eat, and “in-need-of-food” to be influential on PIFP. On the other hand, PIFP was reported to be driven by vitality-related sensations such as energized, relaxation, and concentration. This study suggests that there are similarities and also distinct differences in the cultural constructs of post-ingestive food pleasure in Denmark and in China.

Here, Duerland et al. (2020) studied the subjective sensations linked to appetite, desire, wellbeing and energy, and aimed to determine the impacts of these sensations on snack choice. The 253 participants (with an average age of 20.5) were given six snacks to choose from, while they were also evaluated on subjective sensations using a visual analogue scale. Sensory-specific sensations such as salty, fatty and sweet desires, particularly influenced snack choice, in both a positive and negative manner. Next, sensations connected to a person’s well-being (overall, physical, mental) significantly impacted decisions on which snack to eat. Health-conscious females selected healthy snacks, while males tended to pick the unhealthy option. Thus, this study deduces the notion that sensory-related desires and well-being sensations are important determinants of snack choice. These experiments help us to better understand snacking behavior and could have even bigger implications regarding obesity and other public health issues.

This 2016 study tested the relationship between the level of food processing involved in making a product and people’s glycemic and satiety responses. The food served varied in terms of processing based on the international NOVA classification, which were: raw and minimally processed foods; processed foods; and ultra-processed foods (industrial products made from substances extracted/derived from food additives). Fardet hypothesized that there would be a correlation between the extent to which the product was processed with the satiety index and glycemic response. Glycemic response was assessed based on the glycemic index (GI) and the glycemic glucose equivalent (GGE), a new index that calculates the quantity of glucose needed to induce the same volume of change in the blood glucose concentrations that were observed following intake of the test food. Strong associations were identified between glycemic glucose equivalent (the new index), satiety index, and the level of food processing, while the glycemic index was not found to correlate with degree of food processing. The data suggested that the more processed the food product is, the greater the glycemic response and the lower its potential to achieve satiety. The results are in support of the advice to consume complex and natural, and even minimally and/or processed foods rather than ultra-processed foods if one is searching for weakly hyperglycemic and satiating foods.

Although drinking soup is known to reduce energy intake and increase feelings of fullness, Flood & Rolls (2007) wanted to test several types of soup, as a preload, on their effects on subsequent meal intake. Sixty normal-weight participants visited the laboratory to have lunch with/without a soup preload once a week for 5 weeks. The subjects were given one of four soups: broth and vegetables served separately; chunky vegetable soup; chunky-pureed vegetable soup; or pureed vegetable soup. Fifteen minutes after the preload (or no preload), each individual was allowed to consume a test meal. Compared to the control group, who did not consume soup, the intake of the soup preload significantly reduced the amount of the test meal eaten and the total energy uptake by the preload test groups. In fact, those who ate soup took in 20% less energy overall subsequently. But the type of soup was not found to influence meal consumption or energy intake. This study concludes that the consumption of a soup preload (many options on soup types) can assist in moderating people’s energy consumption.

In the first of two crossover studies conducted by Duszka et al. (2020), the participants were shown random non-food related pictures on the first day and food related photos on the second day. Following the picture-viewing session (as part of the second study) the subjects were asked to drink milkshake and have their glucose, triglycerides and several hormone levels checked. The study found that regulation of total ghrelin concentration following food stimulation (through seeing food pictures) is highly individual. Responders had higher ghrelin levels, while the concentrations decreased following a meal. In addition, the color intensity and protein content of the foods displayed in the pictures were negatively associated with individual ratings of the pictures. The researchers suggest that the protein content of foods and green color intensity of pictures have an impact on the attractiveness of the food/meal. It was also concluded that the concentrations of several appetite-related hormones are disturbed by the viewing of food pictures. This connection between visual cues and physiological response is likely to be clinically relevant.

Grabenhorst et al. (2008) state how important it may be to understand how cognition alters the brain regions that are affected by taste and flavor of foods - not only for obtaining more information on the top-down influences of the brain, but also to dig deeper into the issue we have in obesity and appetite control. Brain activations related to the umami taste and flavor (discovered through correlations with pleasantness ratings) were modulated by how the object was described using words and expressions, according to the functional magnetic resonance imaging results. The affect-related activations associated with taste were modulated in the pregenual cingulate cortex, while another region called the ventral striatum responded to taste and flavor. The intensity (not the pleasantness) of taste appeared to induce responses in the insular taste cortex, although affect-related cognitive modulations were not discovered in this region. It was concluded that top-down language-level cognitive influences are even present in the earliest cortical areas that correspond to the appetitive value of taste and flavor. In this way, cognition does modulate the neural mechanisms linked with controlling appetite.

In this 2019 crossover trial, 20 weight-stable adults were admitted to a clinic and randomized to receive either ultra-processed or unprocessed diets for 2 weeks, followed immediately by the alternate diet for another 2 weeks. The subjects were given unrestricted access to each meal, which were designed to be matched in terms of calories, energy density, macronutrients, sugar, sodium, and fiber. The research found that energy consumption was significantly greater when participants were on ultra-processed diets, compared to when eating unprocessed meals. Intakes of carbohydrates and fats were higher while on ultra-processed meals, but protein consumption was not greater. Furthermore, weight gains of 0.9 ± 0.3 kg were observed during the ultra-processed diet, while the unprocessed diets were associated with weight loss of 0.9 ± 0.3 kg (both statistically significant). Weight changes were highly correlated with energy intake. This data suggests that limited eating of ultra-processed foods could be an effective strategy for weight control and obesity management.

This 2020 study assessed the brain’s response to different food odors and aimed to determine its association with energy density and individual body mass index (BMI) changes over a 2-year period. Twenty-five participants were presented with several different odors (high-fat/chocolate & peanut, low-fat/bread and peach, non-food/rose) while undergoing functional magnetic resonance imaging (fMRI) to examine brain activation. The weight and height of each subject were collected also during the fMRI scans and 2 years later to calculate the body mass indices. The results showed inverse correlations between increase in BMI over the 2 years with the brain activation in response to high-fat vs. low-fat food odors. Another association was detected between greater brain activation in food vs. non-food odor with the subsequent increase in BMI over 2 years. To summarize, these findings suggest that individual variation in neural responsiveness to high-calorie foods in certain brain regions may be used to predict future changes in BMI.

Hermann et al. (2019) writes that while the measuring of food cue reactivity through functional magnetic resonance imaging (fMRI) can help determine people with dysregulated reward brain systems and increased susceptibility to environmental cues that tend to cause obesity, weight loss interventions have more recently been shown to possibly influence fMRI food cue reactivity. This is why this present study assessed whether fMRI food cue reactivity could be used to predict diet-induced early changes in neural processing in the striatum region of the brain that can indicate the outcome of the weight loss intervention. This study examined the food cue reactivity of the participants one month after the start of the weight loss program, as well as their relationship with weight changes observed at the end of the six-month intervention. A significant association was found between BMI changes after the six months with early transformations in fMRI food cue reactivity in the striatum. This study has provided evidence of the diet-induced early alterations in fMRI food cue reactivity in the striatum that can predict the outcome of weight loss interventions.

The influence of verbal labeling on the perception of odors: evidence for olfactory illusions?

In this 2012 study, the main meal recipes created by television chefs were assessed and compared with ready meals sold by supermarkets on energy and macronutrient content, and also on their adherence to nutritional guidelines. Howard et al. analyzed 100 recipes from the five best-selling cookery books by UK television chefs and 100 own brand ready meals from the three leading UK supermarkets. The outcome measures included the number of meals for which the nutritional content complied with recommendations published by the World Health Organization (WHO), and the proportion of nutrients classed as either red, amber, or green according to the UK FSA’s “traffic light” system for labelling food. The study found that although none of the recipes nor ready meals complied with the WHO recommendations, the ready meals were more likely to comply with the recommended percentage of energy obtained from carbohydrates, sugars, and fiber density (all p ≤ 0.05). The chefs’ recipes had a greater chance of complying with the recommended quantity of sodium, but the author notes that salt used for seasoning was not included in the assessment. The most common traffic light color under the FSA’s food labelling recommendations was red for the recipes (47%) and green for the ready meals (42%). Moreover, the recipes were made up of significantly more energy, protein, fat, and saturated fat per portion than the ready meals.

Since the human brain naturally optimizes the contribution of different resources when in pursuit of rewards, Kringelbach et al. (2012) think that food consumption follows a similar cyclical time course to other rewards with stages of expectation, consummation (completion), and satiety (fullness). This article presents an evidence-based multilevel model for the full cycle of dietary behavior, and attempts to describe the relationship between the underlying reward mechanisms of wanting, liking and learning, and food intake regulation involving hedonic (pleasure-related) and homeostatic principles. Five of the main principles governing food consumption are: hunger and attentional signal processing; motivation-independent discriminative processing; reward representations; learning-dependent multimodal sensory representations and hedonic experience. It is clear that there has been an overall increase in knowledge on underlying mechanisms and brain networks, although human food intake is complex.

Examining the influence of duration of the cue exposure and trait impulsivity. Appetite, 58(3), 907–913. The objective of this 2012 study was to examine whether the impact of olfactory (relating to sense of smell) food cue exposure on young women’s food intake is moderated by the duration of the cue exposure and trait impulsivity. This study was designed as a 2x2 between-participants trial, meaning that each subject would experience 4 conditions varying in food cue exposure (baked cookie smell or no smell) and duration of cue exposure (short- or long- term). The 109 normal-weight women who took part were assessed on food consumption during a bogus taste-test, and tested on several saliva measures during the cue encounter. The results demonstrated that low-impulsive females ate more food when faced with an olfactory food cue, whereas no significant difference was detected among the high-impulsive women who experienced the same food cue. The evidence indicated that the subjects’ food consumption were not influenced by the duration of the cue exposure, but moderated by impulsivity, and not by saliva flow. Larsen et al. state that the findings may be explained by the lack of instructions communicated to the women to focus on the food cue. The research ultimately uncovered that individuals who are normally well-controlled are susceptible to the power of less explicit olfactory food cues.

Although longer oral processing is believed to reduce people’s food intake due to a lower eating rate (ER) and longer exposure of the food to the person’s oral senses, Lasschuijt et al. (2020) claim that we have yet to fully understand how these factors contribute to food consumption, including the underlying physiological mechanisms. Two studies were conducted to analyze the individual and combined impacts of oro-sensory exposure (OSE) and eating rate (ER) on satiation (feeling of fullness) and related responses. The 2 studies were designed as 2x2 randomized trials whereby participants ate chocolate custard with added caramel sauce (low OSE) or caramel fudge (high OSE) and with short (fast ER) or long breaks (slow ER) in between bites, until the point of fullness. Study 1 recruited 40 subjects, while the second study involved 20 participants and measured endocrine (related to hormone-producing glands) responses during the meal. In the first study, the subjects ate 42 ± 15 g less when they were permitted long breaks between bites than the short-break condition, but only while eating chocolate custard with caramel fudge (high orosensory exposure). In study 2, 66 ± 21 g less food was consumed in the high- (caramel fudge) than in the low-OSE condition (caramel sauce) and there was no variation in intake between the slow and fast eating rate conditions. Insulin levels rose by 42%-65% eight minutes after eating in all treatments compared to the control, and at the end of the meal, were also 81% higher in the high-OSE, slow-ER than in the low-OSE, fast-ER condition. Pancreatic polypeptide concentrations increased by 62%, 5 min after meal onset in the low-OSE, fast-ER condition, but ghrelin levels were not significantly altered. The researchers concluded that greater orosensory exposure enhances insulin responsiveness, and that pancreatic polypeptide responses are stronger when OSE is low and eating rate is fast. This data may benefit type 2 diabetic patients especially with the control of their blood glucose levels and food intake.

Since higher food viscosity leads to longer stimulation of the oral senses, Mars et al. set out to study the metabolic responses associated with these sensory signals that are firing during consumption. This study specifically looked at the impact of food viscosity on people’s learned satiation (feeling of fullness). To begin, the participants were split into 2 intervention groups: one that was offered unlimited access to a low viscosity (LV) yoghurt for breakfast; while the other group received as much high as they wanted of a viscosity (HV) yoghurt. Later, in the 4-week learning period, the subjects had an unlimited supply of either a high energy density (HED) yoghurt or a low energy density (LED) yoghurt, while being exposed to each yoghurt 10 times a day on alternate days. There was a significant link found between exposure and energy density among the high-viscosity intervention group. For example, 46+/-16 g more of the low energy density yoghurt was eaten after 10 exposures, compared with the high energy density yoghurt. However, there was no notable relationship between exposure and yoghurt energy density in the low-viscosity intervention group. These results seem to suggest that higher viscosity foods support learned satiation.

While consuming diets high in sugar and fats lower taste sensations, alters food choices, and facilitates feeding, May et al. (2020) planned to find out how these changes influence eating by using a genetically tractable (modifiable) organism called D. melanogaster. The scientists monitored the activity of a specific set of neurons in the organism referred to as PAM DANs that responds to sweet taste, by focusing on a part of the mushroom body that is supplied by PAM DANS with nerves (β’2). In animals fed a high-sugar diet, lesser and delayed responses were seen in this PAM-β’2 section, which also showed sensitivity to the strength of the signal transmission out of the sensory neurons. Moreover, there was evidence that PAM-β’2 DANs activity controls feeding rate and satiation (feelings of fullness). The findings suggest that diet-induced taste changes weaken satiation by blocking the processing of some sensory signals.

While sensory food cues have been shown to stimulate the secretion of saliva, Morquecho-Campos et al. (2019) wanted the effects of changing food odors and olfactory (smell-related) stimulation on saliva secretion and composition, respectively. In the first study, 36 individuals were randomly exposed to no-odor, non-food, and odors that are perceived as sweet, savory, and sour taste. While the second study involved 60 participants who were randomly tested with no-odor, non-food, and odors signaling carbohydrates, protein, fat, and low-calorie food. Their whole-mouth saliva was collected and assessed for secretion rate, subjective salivation, visco-elasticity, mucin concentration, α-amylase and lingual lipase activity. Both studies provided evidence that food odors significantly increased saliva secretion rate compared to no-odor and non-food conditions. However, there were no apparent differences in salivary composition. Nevertheless, this data reveals that food odors can greatly influence anticipatory saliva responses and therefore can alter dietary behavior.

In this 2007 study, Mourao et al. investigated the influence of changing food form on the appetite and energy intakes of lean and obese adults. The matched solid and beverage foods analyzed were: watermelon and watermelon juice (to represent high carbohydrate stimuli); cheese and milk (high protein); and coconut and coconut milk (represents high fat). As a crossover design, 40 participants (20 lean, 20 obese) of the 120 in total were tested with each of the food systems. The results showed that the beverage form induced a weaker compensatory dietary response than its matched solid food form, regardless of predominant energy source. This means that total daily energy intake significantly increased after consuming the beverage forms of the high-carbohydrate (12.4% increase), -fat (19%) and -protein foods (15%). It appeared that food form weakly affected satiety (the feeling of being full) rather than satiation (state of fullness). Although obese participants took in higher amounts of energy at lunch, there was no marked overall difference in energy consumption between the lean and obese groups. Since people did not show much dietary compensation for consuming beverages than solid foods of similar nutritional content, beverages may heighten the risk of gaining weight.

While we know that the sensory properties of foods largely determine palatability, the aim of this 2012 study was to find out how these sensory properties can influence how much we eat. The 40 participants were female and classified on their sensory sensitivity (high/low) using scores on the Adult Sensory Profile (a measure of sensory processing). After measuring their chocolate intakes during the experiment, it was discovered that the high-sensitivity individuals ate significantly more than the low-sensitivity subjects. There was a positive correlation between sensory sensitivity scores with emotional eating. These results suggest that people with higher sensitivity to sensory properties of food are more likely to consume greater amounts of food due to the heightened perception of palatability.

This 2000 study states that cephalic phase responses (CPRs) are physiological responses to sensory signals that prepare the body to optimize digestion or compensate for unwanted changes during a meal. According to the cue reactivity model of binge eating, CPRs are experienced as food cravings and lead to increased eating. Nederkoorn et al. therefore set out to investigate CPRs and their relationship with food intake, craving, and restraint. Upon food exposure, many changes were observed in the participants, including heart rate, heart rate variability (HRV), salivation, blood pressure, skin conductance and gastric (stomach) activity. Other findings included the strong interactions between restraint and blood pressure, blood pressure and craving, and craving and food consumption. Conducting research on physiological CPRs and craving is crucial in the field of eating disorders.

This 2011 study assessed the impacts of sensory specific satiety (SSS) and sensory specific desire to eat (general wanting for certain taste categories) on the subsequent food choices of children and adults. The 87 children and 49 adults who participated in this study were fed sweet pear banana yoghurt until satiation (fullness) and were tested on foods representing sweet, salty, sour, bitter, "fatty", and "spicy" flavors too. The hunger, satiation (state of fullness), liking, and wanting for the test foods and the yoghurt were reported at baseline and after meal consumption. Sensory specific satiety and sensory specific desire were expressed differently in children and adults. The children’s sensory specific satiety was bound to the yoghurt, whereas a transfer in SSS was observed in adults to the uneaten foods sharing sensory characteristics with the yoghurt (namely sweet, sour and "fatty"), reducing their liking after intake. The same trend was seen for sensory specific desire to eat. These variations in expression of SSS and SSD between adults and children may have major implications for the planning of meal compositions.

Since morbidly obese people are said to be more sensitive to sensory cues than lean people, Proserpio et al. (2019) assessed the effect of exposure to ambient odor on sensory-related appetite and food intake among an obese female sample. The thirty obese participants attended 2 sessions, in one of which they were exposed to a mild concentration of a bread odor, and the other in which the test room was “unscented”. Questionnaires on appetite were completed before entering the test room, while questionnaires on sensory-specific appetite were administered 10 minutes after being introduced to the “scented” or “unscented” condition. Fifteen minutes into being in the test room, the subjects were given unrestricted access to a low-energy dense vegetable soup. Compared to the “unscented” odor exposure, the “scented” condition raised the quantity of soup consumed by the women. The sensory specific appetite of the ladies were also induced by the ambient odor for food products similar in terms of taste and energy density, resulting in significant increases in general appetite scores. These findings may have important implications for helping to reduce the energy intakes of individuals.

Although the processes behind the control of homeostatic feeding (required for basic metabolic processes and survival) and hedonic feeding (related to sensory perception or pleasure) are often considered separately, Rossi & Stuber (2018) believe there is a link between the two. Data indicate that many neural circuits that govern feeding behavior also are involved in the brain’s reward system (anatomically and functionally). Moreover, food consumption and reward can be influenced by altering several neural pathways. The authors ask their fellow researchers to look beyond food intake when investigating the neural control of feeding, and take into account other behaviors. This research is regarded to be crucial since the central regulation of food consumption is a key mechanism contributing to energy homeostasis.

While unconscious cognitive and behavioral processing have been found to be related to food, Sato et al. (2016) wanted to investigate affective (relating to moods, feelings, and attitudes) responses to food, its relationship with daily dietary behaviors, and whether it can be triggered unconsciously. The participants were exposed to a photo of either food or mosaic images, before being presented with photos of faces with emotionally neutral expressions. When asked to rate the face photos, subjects preferred the subsequently shown photos after viewing the food images, compared to the mosaic one. Moreover, in individuals who engaged in greater external eating, there was likely to be a larger difference in preference induced by the food images versus the mosaic pictures. These findings suggest that seeing food does provoke unconscious affective reactions, which are thereby likely to contribute to eating behaviors related to overeating.

Serrenho et al. (2019) describe ghrelin as an appetite-stimulating hormone produced by peripheral organs that play a part in signaling pathways when the energy status of the body changes, and regulate food intake, body weight, and glucose homeostasis. It has also been claimed by research studies that ghrelin is involved in cognition, and hedonic (pleasure-related) and homeostatic feeding. Since ghrelin-induced synaptic plasticity has been mentioned in neuronal circuits associated with aforementioned behaviors, this review inspected the neuromodulatory mechanisms induced by ghrelin in regulating synaptic plasticity in the circuits previously linked with feeding behaviors. As well as its connection with feeding behaviors, modified ghrelin concentrations is believed to correlate with metabolic disorders such as obesity and anorexia, emphasizing the importance of better understanding ghrelin and its impact on the synaptic plasticity of influential neuronal circuits.

This article by Seo (2020) highlights the recent data found on how sensory cues based on environmental cues can modulate consumers’ perceptions, emotional responses, and behavior related to foods and beverages. The author claims there has been a rise in interest in environmental cues, which had already previously been reported to influence consumer behavior and perception towards food and drinks. The recent findings, though, may be useful in a wide variety of contexts, including in grocery stores, retail markets, restaurants, dining facilities, and public dining areas. This study may inform many retailers, marketers, business owners, and sensory professionals, who may benefit from taking into account sensory cues derived from the surrounding environment when it comes to better understanding consumers and their perception, acceptability, and behaviors towards goods.

Given the inconsistent findings on people’s detection speeds for food versus non-food items, Sawada et al. (2017) conducted a study assessing normal-weight individuals on their reaction times in detecting high-fat foods (fast food), low-fat foods (Japanese diet), and non-foods (kitchen utensils) among a crowd of cars (distractors). The researchers were interested in investigating the impact of fat content on food detection since fat content has been shown to affect visual attention for food in the past. The present study results backed up the evidence showing shorter reaction times for food targets than for non-food targets. Also, the participants reacted quicker to spot high-fat food items than low-fat foods. These findings suggest that food is more rapidly seen than non-foods and that higher fat content further speeds up the detection process.

This 2017 study analyzed the effect of 3 food and 3 non-food odors (matched in intensity, pleasantness) on human cerebral activity since perception of food-associated odors, as opposed to non-food smells, are thought to activate dopaminergic brain areas. Thirty participants were exposed to odors derived from edible and non-edible substances while undergoing functional magnetic resonance imaging scans. Among both hungry and satiated (full) subjects, significantly greater activation was seen in the anterior cingulate cortex (right and left), insula (right), and putamen (right) due to the food odor compared to that of non-food. Significant stimulation in the ventral tegmental area was also evident among the hungry sample group after encountering both odor types. These findings prove that the edibility of the odor source influences the trigger of certain dopaminergic brain areas.

While the global food companies are blamed for their role in the growing obesity crisis due to their provision of addictive foods and delivering of easily accessible calorie-rich foods, Spence et al. (2016) investigate whether there are other implicit cues in our environments that are increasing our hunger for foods. Compared to the environments our brains evolved, our current surroundings and especially in the Western world, dietary resources are much more readily available. While the food industry aims to design the perfect concoction of pleasurable ingredients (sugar, salt, fat, etc.), the authors want to analyze the digital impact of constantly viewing images of desirable foods (often labelled “gastroporn” or “food porn”). Our exposure to these pictures may be inadvertently heightening our desire for food. This article reviews the current evidence on the influence of these food images on neural activity, physiological and psychological responses, and visual attention, especially in the 'hungry' brain.

Since food texture is critical in the acceptance of the food by young children, this 2021 study released an online survey for mothers of 4- to 36-month-old children to report on their children’s liking for the 188 food-texture combinations listed [purees (T1), soft small pieces (T2), hard/large pieces, and double textures (T3)]. A total of 2999 mothers sent their feedback on whether the kid(s) ate with or without difficulty, or even spat out the food. The ability to eat foods without difficulty increased with age, while the puree was the most accepted food texture tested at all ages, followed by soft small pieces, and hard/large pieces, and double textures. There was a positive correlation between the global food texture acceptance score calculated for each child (TextAcc) and exposure to soft small food pieces (in the age group 6-18 months), hard/large pieces, and double textures (in the age group 6-29 months), while TextAcc was also found to be negatively associated with exposure to puree among those between 9 and 36 months old. Moreover, maternal feeding practices and feelings towards starting solid foods appeared to play a factor in their children’s acceptability of the varying food textures. But in addition to these feelings, the main factors linked with acceptance included children’s ability to eat with their fingers, gagging frequency, and to a lesser degree, the arrangement or condition of their teeth. This study demonstrates the importance of exposing young children to various food textures and reveals additional factors that are associated with food texture acceptance during the complementary feeding period.

In this 2016 article, Wilkinson & Brunstrom firstly explain the popular belief that sensory specific satiety (the decline in pleasantness associated with a food as it is eaten relative to a food that has not been eaten) is controlled by habituation. Three experiments were conducted to evaluate whether 'top-down' cognitive activity has an effect on expression of sensory specific satiety (SSS). Participants were manipulated on their expectations on whether or not they would have access to alternative test foods (uneaten foods) after consuming a test meal (eaten food). Their desire to eat and pleasantness of the eaten food were thought to drop significantly more when uneaten foods were not available, but none of the findings backed up this hypothesis. Sensory specific satiety was not found to depend on top-down processes associated with the availability of other uneaten test foods.

Although attentional bias to food stimuli were seen in obese vs lean behavioral studies, Yokum et al. (2011) planned to employ functional magnetic resonance imaging (fMRI) to further investigate this observation, and determine whether this attentional bias to food stimuli predicts future weight gain. Thirty-five adolescent girls performed attention network tasks involving food and neutral stimuli, while their attentional biases were being tested using fMRI. As BMI of the participants increased, this correlated with faster behavioral responses to both appetizing and unappetizing food stimuli, but not to neutral stimuli. BMI was also positively linked with stimulation of brain regions related to attention and food reward during first orientation to food cues. Furthermore, greater activation in the lateral orbitofrontal cortex (OFC) region of the brain during initial orientation to appetizing food cues could predict future BMI growth. The results indicate that overweight people may show greater attentional bias to food cues, and that risk of weight gain may be elevated among some youth who demonstrate raised reward circuitry responsivity during food cue exposure.

Ziaduddeen et al. (2012) claim that although hunger may be reduced by the sensory-specific satiety (SSS) phenomenon (which describes the decline in satisfaction gained of the food being eaten relative to another type of food that has not been consumed), certain foods such as desserts remain attractive and encourage energy intake. Since it is important to understand how the dynamics between internal and external driving factors related to eating, this present study was designed to determine whether food stimuli would still induce the same effect even when they are subliminally communicated (unconsciously perceived), and whether this involuntary influence would vary in response to food reward value while sated (full). The results of this study indicate that the SSS phenomenon impact is unaffected by the lack of conscious awareness of external stimuli. Thus, our desire for food appears to be influenced by even the most subtle and subliminal events that take place around us.

While Zijlstra et al. (2009) has observed the impact of food viscosity on food consumption, the team wants to test whether bite size and oral processing time (OPT) also affect people’s intake when food is readily available for eating. There were 7 test conditions in total, including small (about 5g) or large (~15g) bite sizes. While oral processing times were at times fixed (3 or 9 seconds), some conditions would allow the participants freedom to eat at their pace too. The 22 healthy subjects consumed chocolate custard through a tube connected to a pump, and their processing times were indicated by the sound signals made. Food consumption was significantly higher when bite sizes were large compared to when they were small, and also when oral processing time was calculated to be 3 seconds rather than 9. The authors therefore concluded that the participants ate much less by eating small bite sizes and taking a longer time to ingest the food, rather than taking large bites and decreasing oral processing time.

The aim of this 2008 experiment was to evaluate the impact of altering food viscosity on food intake (when given unrestricted access) in a real-life setting, and to assess whether a difference in consumption is related to either eating rate or effort. While 108 participants were placed in a real-life setting and given a chocolate flavored liquid, semi-liquid and semi-solid milk-based product (all similar in palatability, macronutrient composition and energy density), 49 subjects consumed the liquid or semi-solid product in the laboratory. The outcome measures were eating rate and effort, which could be determined by feeding the product through a peristaltic pump. The liquid form was reported to have been consumed the most in the real-life scenario at 809+/-396 g, which was 14% more than the semi-liquid, and 30% more compared to semi-solids. Disregarding eating effort in the laboratory setting resulted in a 29% higher intake of the liquid product relative to that of the semi-solid form. Standardizing the eating rate reduced this difference in consumption of the liquid and semi-solid test samples to 12%. If controls were not considered, the variation in quantity eaten between liquids and semi-solids was comparable to the real-life setting. In summary, the level of food consumption is greatly affected by viscosity, even if similar in palatability, macronutrient composition and energy density. The higher eating rates of liquids may play a factor in the difference in consumption observed.

Since food cues exposure through smelling leads to increased appetite for foods similar in taste to that smell, Zoon et al. (2016) set out to test this phenomenon using sweet/savory taste, and to assess whether this effect extends to energy density (high/low) and is modulated by the hunger state. During this experiment, 29 healthy-weight females encountered 4 odors varying in taste and energy density, as well as one non-food odor, and one odorless solution (control). The odors were smelled in random order for 3 minutes each, before the participants rated their appetite for 15 different food products. Analysis models revealed that smelling an odor with a sweet/savory taste predisposed individuals to have greater appetites for sweet or savory food products, compared to incongruent and neutral food products. Odors signalling high and low energy density properties also resulted in similar trends, with higher ratings for high and low energy dense food products following exposure to congruent odors. However, the state of hunger did not significantly affect the subjects’ appetite levels. As these results suggest that encountering food odors raises appetite levels for congruent products with regards to taste and energy density, irrespective of hunger state, food odors could be guiding people to eat more foods with a congruent macronutrient composition.

With the aim of better understanding the role of odors in overeating, Zoon (2017) found that smelling food odors increases appetite for foods similar in taste and energy density to that odor, and decreases the liking and desire for these congruent foods. This article also reveals that following high energy/sweet food consumption, early neural processing of pictures of the same foods changed significantly. Conversely, smelling odors signalling high-energy food, low-energy food, and non-foods did not lead to alterations in food preferences or intakes. But the researchers learnt that patients who undergo Roux-en-Y Gastric Bypass (RYGB) weight-loss surgery start to prefer low-fat/low-sugar foods rather than their previously preferred diet of high-fat/high-sugar foods. In addition, differences in prefrontal neural responses were seen in post-surgery patients, indicating inhibition of response to pictures of high-energy foods. These findings suggest that RYGB weight-loss surgery results in cognitive modifications (control of attention, neural inhibition over behavioral responses). It is therefore concluded that odors have an appetizing function in the anticipatory phase of eating, which implicates orthonasal odors in guiding people’s food decisions towards a healthier eating pattern.

To assess whether overweight and hungry children have an attentional bias for food cues in food advertising, 95 children played an advergame that promoted either high-energy snacks or non-food products, in this 2020 randomized study. The results showed that overweight children gazed longer in response to food cues compared to normal-weight children, whereas this overweight status did not affect attentional bias measurement when encountering non-food cues. Higher gaze duration was also seen in the hungrier children relative to less hungry children, in addition to a higher number of fixations, and faster latency of initial fixation on the food cues. However, the inverse was observed for the non-food cues. As Folkvord et al. expected, food advertising appears to more strongly influence overweight and hungrier children than normal-weight and less hungry children. The food advertisement used in this experiment is highly comparable to the advertisements regularly used by food companies, which demonstrates the high validity of these findings. Furthermore, the children’s attentional biases for food cues was analyzed in a real-life situation.

Since the majority of the evidence on the association between the quality of the American diet and advertising has been reported in children, Zimmerman & Shimoga (2014) planned to determine the impact that televised advertising has on adults’ food choices. The 351 participants were firstly randomized into one of four groups: exposed to food advertising and a cognitively challenging task; food advertising encounter and non-cognitively demanding task; seeing advertising that are non-food related and performing a cognitively tough task; or viewing non-food advertising before performing a non-cognitively straining task. The outcomes measured were the number and calorie contents of the unhealthy snacks selected by the subjects. The data revealed that those exposed to food advertising chose 28% more unhealthy snacks than those who encountered non-food advertising. Moreover, the caloric values of these snacks chosen by the food advertising-exposed half of the sample were 65 kcal higher. The different adverts did not significantly affect the individuals assigned to the less cognitively demanding task, but there was a large and significant discrepancy in influence among the participants that completed cognitively challenging tasks. Those who came across food-related adverts ate 43% more unhealthy snacks, taking in 94 more total calories, compared to the subjects who saw non-food adverts. This research concludes that televised food advertising strongly influences people’s food choices, particularly when these individuals are cognitively occupied.