Diet and Mood

Conner et al. (2020) state that fruits and vegetables containing high concentration of vitamin C have been linked to greater feelings of vitality but rarely has it been studied in randomised controlled trials. This is why Conner and her team of researchers took 167 young adults (61.1% female, aged 18-35) with vitamin C levels of less than 40 micromoles per liter in the blood and randomly assigned them into one of three intervention conditions including, kiwifruit (given 2 SunGold™ kiwifruits to eat every day), vitamin C (250mg tablet daily), and placebo (involving taking 1 tablet daily). The trial consisted of a two-week lead-in, four-week intervention, and two-week washout, and its purpose was to measure the effect of eating the kiwifruit (a vitamin C-rich food) on the participants’ vitality and to find out whether these effects are driven by vitamin C. Questionnaires on vitality and plasma vitamin C were undertaken every 14 days while sleep quality and physical activity was also self-reported every couple of days through smartphone surveys. The trial found vitamin C levels reached saturation levels within two weeks for both the kiwifruit and vitamin C groups. The kiwifruit-consuming subjects improved in mood and well-being during the 4-week intervention period, and these effects were sustained during washout. In the vitamin C tablet group, less fatigue and enhanced well-being were observed but only in those with consistently low vitamin C levels during the lead-in. The three-day food diaries taken also uncovered a reduction in fat intake by the kiwifruit group during the intervention period. No changes in plasma vitamin C status or vitality were found in the placebo group. The effects of these interventions remained significant after adjustments for age and ethnicity were made, and were not explained by sleep quality, physical activity, BMI, or dietary patterns like fat intake. Since kiwifruit consumption correlated with increased vitality in adults with low vitamin C status, a similar but not identical impact to that of vitamin C tablets, these findings suggest that the additional properties of kiwifruit may contribute to improved vitality.

This 2016 study evaluated whether an enhanced level of psychological well-being directly correlates to the quantity of fruits and vegetables consumed. Food diaries from 2007, 2009, and 2013 were taken from 12,385 Australian adults randomly selected in the "Household, Income, and Labour Dynamics in Australia" Survey (HILDA). A greater consumption of fruit and vegetables was found to have a positive relationship with psychological health, shown by the jump in satisfaction points associated with consuming 8 added portions a day. These psychological gains were found to equal the happiness achieved by changing from being unemployed to employed.

Lee et al. (2015) explored changes in mood and cognitive and cardiovascular function in response to a 10-day Mediterranean-style dietary intervention. The foods associated with countries bordering the Mediterranean Sea include legumes, olive oil, and fish, and are linked to a reduced risk of developing depression. This crossover study randomly divided 24 women into two groups differing in diet: one was given a Mediterranean diet for 10 days and the other remained on their regular diet for the same length of time, before the diets of both groups were switched to those of the other group for another 10 days. In this study the Mediterranean diet was found to be a mood enhancer (raised contentment and alertness) and improve memory recall and cardiovascular features. These findings were not affected by the order in which diets were adopted, and shows promise for treating mood disorders long-term.

Using smartphone-based ecological momentary assessment, this 2017 study measured immediate changes in eating happiness levels over eight days. 14 different food types were investigated in this study, including healthy options such as vegetables and high-caloric foods such as sweets. Contrary to popular belief that high-caloric foods elicit happiness and counter negative moods, there were surprisingly comparable results between sweets and healthier foods, and between dinner and snacking. Vegetables had the most profound positive impact on eating-induced satisfaction over the course of the study.

Due to the scarcity of studies using this method, Ocean et al. (2019) decided to adopt the panel data analytical technique to investigate the relationship between increased consumption of fruits and vegetables and psychological well-being. The same individuals were questioned a total of 3 times between 2010 and 2017 as part of the UK Household Longitudinal Survey. The fixed-effects regression estimates using a reversed form of GHQ-12 demonstrated that as the number and frequency of fruit and vegetable intake increased, so did the well-being of the participant. The results suggest that the relationship is robust and the subjective aspect of the study should be negligible. After comparing age with fruit and vegetable consumption, a hump-based relationship was found.

In this 2015 study, eudaemonic well-being and behaviours were measured against fruit and vegetable (FV) consumption in young adults. The experiment involved 405 subjects writing a daily internet diary noting any intake of crisps, sweets, fruits, and vegetables. Greater average eudaemonic well-being, increase in creativity, and intensity in curiosity were seen in those young adults who ate more fruits and vegetables than those consuming less, and on days when participants ate more FV compared to the days when they didn’t eat as much FV. While this study suggests increased FV can improve eudaemonic happiness, creativity and curiosity, there was little evidence of the benefits of eating crisps and sweets.

This 2015 study found positive links between the ratio of Long-Chain Omega 6 fatty acids (LCn-6) to Long-Chain Omega 3 fatty acids (LCn-3) and low eicosapentaenic acid (EPA) and/or docosahexaenoic acid (DHA) biostasis with the incidence of mood disorders, major depressive disorder, and bipolar disorder. This is explained by the implication of LCn-3, EPA, and DHA possessing anti-inflammation properties. Therefore, it is predicted that increased intake in LCn-3 could relieve mood disorder through reducing immune-inflammatory signalling.

This 2017 study examined the association between fruit and vegetable consumption and incidence of psychological distress. It examined 60,404 Australian adults aged 45 and over using the validated Kessler Psychological Distress Scale (K10) to assess psychological distress (indicated by high K10 scores >22) and a short validated questioning system to determine their fruit and vegetable (FV) intake. Participants were examined in 2006-2008 and in 2010 for a follow-up. Lower prevalence of psychological distress was associated with increased FV intake even after both minimal and full adjustments on sociodemographic and lifestyle risk factors. Many of these associations were significant in the medium-level FV consumption but not significant in the highest FV consumer group in fully adjusted models. The results of this study suggest that increasing dietary intake of fruits and vegetables in middle-aged and older adults may help reduce chances of psychological distress, although more research is encouraged to find the optimal quantity.

Since polyunsaturated fatty acids (PUFAs) are abundant in the brain and have been linked to anxiety and depression, Larrieu & Laye (2018) analysed the role of the PUFA omega-3 (ω3) series in the prevention and treatment of neuropsychiatric diseases. The review delves into the potential mechanisms of ω3 PUFAs in altering the neurobiological processes leading up to depression and anxiety.

This 2018 study evaluated whether psychological well-being predisposes older adults to eat more fruits and vegetables. The 6,565 participants of the English Longitudinal Study of Ageing were examined over a seven year span to determine their psychological functioning. Boehm (2018) focused on 17 items of CASP-19 including pleasure, self-realisation, and autonomy. From the initial stages, the participants with a greater sense of well-being were shown to eat more fruits and vegetables. It was also shown that these individuals who started the study with a greater feeling of satisfaction would go on to consume fruits and vegetables for longer over the 7 years (11% reduced risk of dropping below the recommended levels during follow-up).

This 2019 review analysed the potential association between vegetable consumption and mental health. Many studies have grouped fruits and vegetables together and examined their psychological effects but in this review, only research with data on vegetable intake alone was included. The total sample size taken from 10 different studies was 33,645. Out of all the healthy non-clinical adults, two thirds reported feeling better on the vegetable only group in relation to depressive symptoms. When the recommended amount of both fruits and vegetables were eaten, psychological well-being improved. However, its efficacy in reducing negative mental health symptoms was unclear. This begs the question of if more research work should be undertaken on vegetables alone and their potential role in the treatment of psychological disease.

Banta et al. (2019) used the California Health Interview Survey (representing 27.7 million adults’ answers annually) stretching from 2005-2015 to explore the relationship between mental health and dietary consumption. Kessler-6 scores allowed categorisation of the giant cohort into no/low (NLPD), moderate (MPD) and serious psychological distress (SPD). 13.2% of the population studied were found to have MPD, and 3.7% had SPD. After adjusting for a range of factors (including BMI, geography, year, gender, age, race, education, marital status and poverty), the following were significantly associated with MPD and SPD: lower consumption of fruits and vegetables, and increased intake of french fries, fast food, soda, and variance-adjusted daily teaspoons of sugar. In this study, the trends all pointed to the risk of experiencing MPD or SPD rising in individuals who consume unhealthy foods.

Trans fatty acids (primarily from margarines), polyunsaturated fatty acids (PUFAs), and their inverse associations on positive affect and positive associations with negative affect were hypothesised in this 2016 study. The participants, taken from the Adventist Health Study-2, completed a food frequency questionnaire in 2002-2006 before those identified with cardiovascular disease were excluded to create this present study's subset of 8,771. These participants completed the Positive and Negative Affect Schedule (PANAS) in 2006-7, and linear regression analysis was performed (controlling for age, gender, ethnicity, education, body mass index, exercise, sleep, sleep squared, Mediterranean diet, total energy intake, and alcohol). The hypothesis was confirmed; increased trans fatty acid intake was linked to more negative affect (p<0.001), while being inversely associated with positive affect (p<0.001). While n-3 PUFAs could not be associated with either positive nor negative affect, the inverse association between the n-6:n-3 PUFA ratio with positive effect suggests that emotional affect can be improved by not only a low trans fat diet but also by the right n-6:n-3 PUFA ratio.

This short 2020 article sought to analyse the complex relationship between food and mental health, answering questions on carbohydrates, dietary patterns, and bacteria in the gut, and explaining how these factors could be affecting our mood and depressive tendencies. Firth et al. (2020) state that healthy eating patterns such as the Mediterranean Diet are associated with reduced risk of depression and better mental well-being compared to “unhealthy” eating patterns, namely the Western diet. This article links certain foods and eating patterns with glycaemia (concentration of sugars in your body), immune activation and responses, and the gut microbiome to provide insight into how food and mood are closely related. In addition to physical health risks, diets with a high glycaemic index (eg. diets containing high amounts of refined carbohydrates and sugars) are found to be associated with depressive symptoms. High-calorie meals rich in saturated fat appear to stimulate immune activation and inflammation, which is the proposed mechanism by which the Western diet may have detrimental effects on the brain, including cognitive decline, hippocampal dysfunction, and damage to the blood-brain barrier. Moreover, ingestion of probiotics, which theoretically target the gut microbiome, can alter the brain’s response to a task that requires emotional attention and may reduce symptoms of depression. It is highlighted that more research into the complex pathways through which diet and nutrition can influence the brain is required, particularly interventional research investigating if, how, and when dietary interventions can be used to prevent mental illness or reduce its symptoms.

This study conducted a cross-sectional examination of dietary intake, subjective emotional state, and faecal microbial taxa abundances in 133 adults (ages 25-45) without physician-diagnosed mood disorders in order to explore the relationships among their diets, gastrointestinal microbiota, and mood. Habitual dietary consumption was indicated using the National Cancer Institute’s Diet History Questionnaire II, diet quality was evaluated with the 2010 Healthy Eating Index (HEI), subjective mood state was assessed using the 42-item Depression, Anxiety, and Stress Scale (DASS-42), while fecal DNA was also extracted and a region of the rRNA gene was sequenced and subsequently analysed using QIIME2. The data showed sex-dependent associations among 21 bacteria taxa and DASS-42 scores, including an inverse relationship between anxiety scale scores and Bifidobacterium in females and an inverse relationship between depression scale scores and Lactobacillus in males. Furthermore, the total fruit and dairy components of HEI were negatively associated with Depression and Stress scales, respectively. The findings of this study suggest that gastrointestinal microbes are connected to mood in adults without diagnosed mood disorders, that these relationships differ by sex, and that they are influenced by dietary fibre intake. If future gut-microbiota-brain studies were to incorporate dietary intake into their research, they may be able to confirm roles of specific microbes and dietary components in mental health symptoms.

In this 2017 editorial, the aim was to set the scale of the mental illness problem into context while presenting recent evidence linking nutrition to psychological outcomes. Owen and Corfe (2017) wrote that the intent of the 2016 Nutrition Society Winter Meeting, "Diet, nutrition and mental health and wellbeing," was to review where the evidence was strong, where the data was lacking, and to discuss findings with others in the communities working in this area of research. This meeting, as well as the present research in the field, led Owen and Corfe (2017) to theorize that even dietary-based interventions with relatively small effect sizes may significantly reduce the disease burden of mental and neurological diseases.

This 2019 review investigated the benefits of dietary patterns and consumption of certain foods on depression. The balanced Mediterranean Diet was found to reduce risk of depressive symptoms, while the Western Diet consisting of more saturated fats and refined sugars would more likely lead to depression by disturbing gut microflora and reducing nutrient absorption. Furthermore, sugar intake in sugar-sweetened drinks was positively associated with depression, while the consumption of certain foods such as fish, fruits, and vegetables had a beneficial effect on symptoms. The use of the antioxidants green tea polyphenols or isoflavonoid have been shown to reduce signs of depression. The influences of food and nutrients are important factors to consider when clinically treating depression.

This 2014 article describes the complex nature of food consumption and its link with mood and brain signalling, while also touching on the sensations of reward and gratification associated with eating certain foods — the dangerous sequence of biological events that overrides an individual's satiety and hunger signals. This constant search for dopamine, the chemical that activates reward and pleasure centers in the brain, can often lead to overeating and morbid obesity, which in addition stem from many biological factors engaging both central and peripheral systems in a bi-directional manner involving mood and emotions. Overeating and obesity can even result from the changes in food choice and consumption levels induced by altered mood and emotional eating.

This 2019 systematic review searched 6 databases (PubMed, Cochrane's Library, Science Direct, Scopus, Google Scholar, and ISI Web of Science) for current literature on the association between diet and mood. The Newcastle-Ottawa Scale and Jadad scale for reporting randomized clinical trials were utilized to measure the quality of the 18 studies that met the inclusion criteria and were later included in this review. The findings were not consistent across the studies, although it appears that diets such as DASH, vegetable-based diets, as well as glycemic load-based, ketogenic, and Paleo diets are perhaps the more effective mood-enhancing diets. Arab et al. (2019) concluded that more research is required to examine this relationship over a longer time period to confirm associations at this point.

This 2020 systematic review was conducted to evaluate the relationship between fruit and vegetable intake and mental health in adults, using peer-reviewed observational studies found on either PubMed or Web of Science databases. Further searches were performed manually through inspection of references from the included studies, which increased the number of included studies for the narrative synthesis of findings to 61. The majority of studies were centered around depression and depressive symptoms, although a range of characteristics were assessed overall, from quality of life to attempted suicide. Głąbska et al. (2020) highlight a particular set of findings that indicate greater overall consumption of vegetables and fruits, as well as some subgroups (berries, citrus, and green leafy vegetables) may increase optimism and self-efficacy, while reducing psychological distress, cancer fatalism, ambiguity, and contributing to the prevention of depressive symptoms. It was difficult to compare the findings of all the studies given the variations in methodologies and samples used, which was a limitation, but the review as a whole concluded that fruits and vegetables, processed and natural, as well as their specific subgroups, may elicit positive effects on mental health. The authors advised to consume at least 5 selections of fruit and vegetables daily to improve mental health.

Armstrong et al. (2012) identified the lack of data on what impact mild dehydration has on cognitive function, and thus this study investigated mild dehydration among 25 female participants (age 23.0 ± 0.6 y), achieved by intermittent moderate exercise without hyperthermia, and analyzed its influence on the women’s cognitive function. Three 8-hour placebo-controlled experiments were set up for the women, involving a different hydration state each day: dehydration through exercising without diuretic (DN); exercise-induced dehydration as well as 40mg of the diuretic, furosemide (DD); and euhydration (EU). Cognitive ability, symptoms of dehydration and mood were all monitored during each experiment, 3 times at rest and during each of 3 exercise sessions. The DN and DD trials, when pooled together, achieved a 1.36 ± 0.16% loss of body mass. When the various pooled readings were compared with the EU group, the adverse effects of dehydration were evident both at rest and during exercise when looking at vigor-activity, fatigue-inertia, and total mood disturbance scores of the Profile of Mood States, as well as for task difficulty, concentration, and headache (as assessed by questionnaire). However, cognitive performance was unaffected, and the serum osmolarity, which is an indicator of hydration level, was actually higher in the coupled DD-DN trials, compared with the EU group. To conclude, inducing 1.36% dehydration in females lowered their concentration levels and mood, and increased headaches and perception of task difficulty. Now warranted are studies investigating optimal hydration during and after moderate exercise.

Firth et al. (2020) are keen on understanding the dynamic between diet and mental health, in particular which specific foods and dietary patterns are related to mental health conditions. The most common of these mental health conditions are depression and anxiety, which affect a vast percentage of people both in their function and health-wise. New approaches are needed to better manage clinically diagnosed and subclinical depression and anxiety. But diet-related studies over the last few years have linked specific dietary patterns such as Mediterranean or healthy, and the high consumption of fruits, vegetables, nuts, and legumes, and moderate intake poultry, eggs, and dairy products, with reducing risk of developing depression. But there are other factors to consider when analyzing diet’s relationship with mental health, such as barriers to maintaining a favourable diet (finances, side effects of medications, and other environmental factors). Humans can also make different food choices based on their temporary psychological state - eating “comfort foods” at periods of low mood for example. This review discusses this important but complex, multidirectional relationship between diet and mental health.

Dietary patterns and mental health after myocardial infarction

An electronic ecological momentary assessment study to examine the consumption of high-fat/high-sugar foods, fruits/vegetables, and affective states among women