This study represents the only randomized controlled trial on young adults to date demonstrating that a diet intervention can reduce clinical symptoms of depression. Research is increasingly showing an association between poor diet and depression, while a healthy diet containing fruit, vegetables, fish, whole grains and lean meats and fish are showing an association with positive mental health. This study by Francis et al (2019) enrolled 101 young adults who had both symptoms of depression, and who consumed a poor diet, into two groups: a diet group (placed under a healthy diet intervention) and control group who continued with their habitually poor diet (Editor’s note: complete data for thirty-eight of the 101 individuals was analyzed). Measures were taken at baseline (before intervention) and after the intervention to determine each group’s symptoms of depression, mood, self-efficacy, and memory. The diet group reported lower depressive symptoms after the intervention compared to the control group. In this study, diet intervention reduced depression scores among young adults.

Eating Behavior and Relationships with Stress, Anxiety, Depression, and Insomnia in University Students In a study exploring the relationship between food consumption and the psychological health of young adults, Ramón-Arbués and his colleagues (2019) administered the Healthy Eating Index (HEI), Depression Anxiety Stress Scales (DASS), and the Insomnia Severity Scale to 1055 university students to examine the relationship between their dietary intake patterns and their experienced levels of depression, anxiety and stress. The study results revealed a significant correlation between these variable (unhealthy eating and anxiety, depression, and stress). The authors also identified that excessive intake of sweets accompanied by low consumption of dairy products resulted in psychological and sleep disturbances. These findings indicate that interventions designed to support healthy food consumption in the university student population could lead to psychological health improvements.

Głąbska et. al (2020) provides us with a systematic review of observational studies focusing on the association between fruit and vegetable intake and mental health in pre-schoolers and school-aged children. A total of 12 studies were picked out from the Pubmed and Web of Science databases, all of which were in English and dated up to June 2019. These studies included fruit and/or vegetables and products like juices, and various aspects of mental health such as general well-being, behavioural difficulties and problems, depressive symptoms, emotions, stress, or even depressive symptoms combined with anxiety. The researchers found that in most of the relevant studies, enhanced fruit and vegetable intake had a positive effect on mental aspects of health in pre-schoolers and school-aged children, although the reviewer urges more research on the area in a new sample group, and also points out many studies ended up recommending a generally more healthy dietary pattern rather than increasing fruit and vegetable consumption alone.

While observational studies are demonstrating an association between healthy dietary intake and mental health, this study aimed to elucidate some of the biological mechanisms underpinning this association. Specifically, the study examined the relationship between dietary patterns, BMI (Body Mass Index), and mental health. The study’s author and her colleagues (2018) collected data from 843 adolescents at age 14 and 17 respectively, along with BMI (body mass index) and biomarkers of inflammation (the hormone leptin and C-reactive protein). Findings indicated that a high intake of Western foods, including meat, takeaway foods, refined foods, and sugary foods, at the age of 14 was associated with a higher BMI. And that this higher BMI, by the age of 17, was associated with not only higher BMI, but higher biological markers of inflammation, depressive symptoms and mental health problems. This study provided increased understanding of some of the biological pathways occurring from the Western dietary pattern that connect this pattern with depression and mental health issues in adolescents.

O’Neil and several colleagues (2014) provide us with a systematic review of 12 studies assessing the link between eating habits and behaviours, and mental well-being in children and adolescents. By focusing on a variation of studies (9 using diet as the exposure, 3 using mental health as the exposure), the team finds significant evidence of the connection between poor-quality diets and bad mental health, and unveils highly-likely trends for the reverse. The methodological quality of the studies used were evaluated, and even when selecting only the higher quality studies the results pointed to the same conclusion in all but one trend. This review further strengthens the association between unhealthy diet and mental health in early life.

This robust systematic review scoured through around 1000 research articles from 5 decades to find out for us the relevance of good quality diets and eating habits with positive psychological health at all ages including adolescence. After analysing 56 relevant studies, Khanna et. al (2019) finds considerable differences in mental well-being depending on diet (consuming fruits and vegetables, fish, olive oil, nuts, and certain dairy products can positively affect depressive symptoms), whereas the western dietary patterns and behaviours have been linked with increased risk of depression. This current study proposes greater consideration of dietary requirements in the prevention and treatment of mental disorders.

This study assessed 14-year old adolescents from the Western Australia Pregnancy Cohort (Raine) Study in their dietary pattern and behaviours to discover the relationship between the two. The participants were categorised into 2 groups (Western and Healthy Diet) using factor analysis and a 212-item food frequency questionnaire. The results from general linear modelling were adjusted for total energy intake, body mass index, physical activity, screen use, family structure, income and functioning, gender and maternal education at pregnancy. The Child Behaviour Checklist (CBCL) scores (used to judge behaviour) showed significantly higher signs of withdrawal/depression, delinquency/aggressiveness in the Western diet population, and more positive results for the 14-year olds consuming more fruit and leafy green vegetables. The results point to the worse behaviours linked to the Western diet and enhanced behavioural outcomes to a higher intake of fruits and green leafy vegetables.

In this self-reported study, 171 low fruit and vegetable-consuming young adults (aged 18-25) were assessed over a 14-day period to determine the psychological advantage of increasing the amount of fruit and vegetables (FV) in their diet. There were 3 groups involved in this study: the control group maintained on their usual diet; “EMI” group given text message reminders to eat more FV (fruits and vegetables) and a voucher to spend on FV; and an “FVI” group who were provided with 2 extra portions of FV to supplement their normal diet. The psychological measures reported every night by the participants were: depressive symptoms and anxiety measured pre- and post-intervention, and daily negative and positive mood, vitality, flourishing, and flourishing behaviors (curiosity, creativity, motivation). The findings included better mental outcomes when young adults were given extra fruit and vegetables (FVI) rather than the method reminding people to increase their FV intake (EMI). Although there was no significant difference in their signs of depression, anxiety or mood over the 14 days, a rise in vitality, motivation and flourishing were seen in these young adults.

This Iranian study investigated the relativity of dietary inflammation with predisposition to depression in 300 female adolescents (aged 15-18). Their diets were monitored using a validated food frequency questionnaire, and assessed with regards to inflammatory potential using the dietary inflammatory index (DII). A 21-point Depression, Anxiety and Stress Scale (DASS) was employed to gauge depression levels. The data strongly associated female teenagers with the most pro-inflammatory diets and higher DASS depression scores. They were found to be 3.96 times more likely to have at least moderate signs of depression (DASS>6) compared to those with diets lowest in inflammatory potential, although 30% (88) of the females who participated showed at least signs of moderate-level depressive symptoms.

Mikolajczyk and his team (2009) conducts a cross-sectional multinational survey on first-year university students in Germany, Poland and Bulgaria to draw comparisons between nutritional intake, stress and depressive symptoms, and to explore any variations between the results of each country. The tests conducted on the students include the Cohen’s Perceived Stress Scale (to assess stress levels), a 12-item food frequency questionnaire (looking at diet quality), and a modified Beck Depression Index (to rate depression levels). The results demonstrated a variation in all 3 factorial tests between the countries and gender. None of the male student groups were linked to perceived stress or depression risk, whereas, higher perceived stress reported could be related to more frequent intake of sweets and fast food. A decrease in fruit and vegetable consumption was also associated with depressive symptoms in the female students.

Since the college lifestyle may limit access to healthier foods and has been linked with mental health problems due to its stressful nature, young adults in Appalachia were studied on their diet (mean fruit and vegetable intake, mean added sugar intake), and their mental well-being (average number of depressed days, and average number of anxious days over a 30-day period). The relationship between diet quality and mental health was analysed using a series of statistical analyses to find a number of significant predictors of depression and anxiety in both sexes. Food insecurity was observed in 36.7% of the students, and proved to be a significant predictor in both males and females. Another significant predictor in males was fruit and vegetable consumption. The trends in terms of anxiety were identical in both young men and women in this study (both food insecurity and added sugars intake could be used to significantly predict anxiety risk). These findings suggest improving college students’ diet by facilitating access to nutritious food can help students psychologically.

In this cross-sectional study, the tie between eating patterns and mental health problems (gauged by the use of the Strengths and Difficulties Questionnaire) was investigated in a young Norwegian population (12-13 years old). Parents reported dietary intake through a modified Food Frequency Questionnaire (FFQ) which was then analysed to determine eating patterns (through principal component analysis). The results showed increased signs of psychiatric and hyperactivity-inattention disorders in adolescents on a less ‘varied Norwegian’ eating pattern, and in those with eating habits high in the ‘junk/convenient’ category, than the children who scored lower in scale. A higher score on a ‘snacking’ eating pattern was also correlated to higher risk of conduct/oppositional disorders than lower scores. The study concluded a strong correlation between diversified nutrient-rich diets and enhanced mental health, and the association between poor dieting and irregularly eating habits with poor mental health outcomes at the adolescent stage, independent of physical activity, sedentary activity and background variability.

This 2019 Japanese study focused on the impact of varying dietary patterns on mental health in 320 female university students. The Food Frequency Questionnaires (FFQ) were completed by the cohorts to determine how frequently the female students ate, and their psychological health were monitored using a 28-item General Health Questionnaire (GHQ-28). The data allowed the tested population to be divided into distinct categories of diet patterns including “the light eating pattern” who consumed less but higher intakes of soft drinks, and the “dairy products pattern” which consisted of students consuming higher quantities of dairy products and sweets. This “dairy products pattern” group was significantly associated with higher GHQ-28 scores in the anxiety and insomnia subscale. In this study Takagi and colleagues (2019) demonstrates a link between dietary patterns and mental health status of Japanese female university students.

Mrug et. al (2019) explore the potential role of sodium and potassium excretion in depression by collecting overnight urine samples from adolescents growing up in low-income urbanised neighbourhoods. Samples were taken at the start of the study from 84 adolescents, half of whom were male, and 95% African-American. Depressive symptoms were self-reported at baseline and at the 1.5 year stage, and comparisons were drawn after adjusting for age, BMI, pubertal development and baselines depressive symptoms. The results showed severe depressive symptoms could be predicted by high sodium and low potassium levels in urine and highlighted no variation in trend between male and female. This implies diets made up of high sodium and low potassium content can predispose adolescents who live in poorer, urban areas to develop symptoms of depression.

This Greek study (2019) inspected the data of 2240 schoolchildren who took part in the 2007-2010 Health Growth Study to explore whether an association exists in children aged 9-13 between behavioural lifestyle factors and emotional functioning. The schoolchildren self-reported their daily consumption of products such as fruits, vegetables, and soft drinks via 3 dietary recalls over 24 hours, and also their physical activity and sedentary behaviour were disclosed daily. The Dartmouth COOP Functional Health Assessment chart and the World Organization of Family Doctors Chart was was used to measure emotional functioning. The results indicated a series of statistically significant trends: a greater risk of experiencing emotional impairment was seen in the female population compared to male schoolchildren, and also observed in those classed in the obese/overweight group rather than normal weight. When less than a 1 hour daily average of physical activity was compared to 3 hours of daily average activity, the emotional functioning significantly improved in those who were more active. The data also associated consuming soft drinks with a reduction in emotional ability in comparison to non-drinkers. These results demonstrate the interlinking relationship between physical and emotional functioning in these 9-13 year olds, and encourage further research into the physical and mental nature of diseases in schoolchildren, and potentially targeting both in their treatment.

This longitudinally study analyses bi-directional associations between healthy lifestyles and mood disorders. Young adults (aged 26-31) were assessed at baseline and at the 5 year mark, for diagnosis of depression or dysthymia (persistent depression) and questioned on their lifestyle – (i.e., body mass index (BMI), smoker status, alcohol intake, recreational physical activity and healthy diet). The covariates included age, sex, socio-economic position, parental and marital status, social support, major life events, cardiovascular disease history, and self-rated physical and mental health. Independently of these factors, the risk of experiencing first episodes of mood disorders dropped 22% in those with higher lifestyle scores at baseline. An existing mood disorder at baseline was associated with lower incidence of improvement and greater chance of worsening in lifestyle choices. Healthy lifestyles may be mainly talked about in the promotion of preventing cardiovascular disease but this study implies they are closely related to mood disorders and mental health.

Healthy college students were selected to participate in this double-blind, placebo-control and randomisation-control study, investigating the effect of taking probiotics on anxiety and related factors such as worry, anxiety control, affect and negative mood regulation. The tested group (average age 20.59 and 75.6% female) completed a survey at baseline before being assigned to a condition, which consisted of four probiotic conditions, and one placebo. After 28 days the young adults filled out the survey again to allow data analysis comparisons. The results showed intake of probiotics lessened panic anxiety, negative affect, worry, panic anxiety and improved negative mood regulation. Moreover, further improvements were seen in those who expressed greater distress than those with normative distress. This study suggests the colony-forming unit (CFU) of the pro-biotics were a more significant factor than species counts in the reported positive changes, and that probiotics may have therapeutic potential in the management of anxiety.

This study looks at the relationship between fruit and vegetable consumption and mental health in a British population and especially accounting for ethnicity, parenting and socioeconomic situations. 4683 adolescents aged 11-13 were extracted from the British multi-ethnic Determinants of Adolescents (now young Adult) Social well-being and Health (DASH) longitudinal study, and followed up after 3 years. Mental health was assessed through the Strengths and Difficulties Questionnaire as mean Total Difficulty Score (TDS) and participants were classed as probable cases of mental disorders if scores reached 17 (higher indicating increased psychological distress). After questioning the study group on the number of fruits and vegetables (FV) consumed daily, around 60-70% answered <5 portions, 20-30% with <1 servings per day. Data revealed the majority of ethnic minority groups were consuming less FV than their white peers. The value <1 portions of FV a day was still significantly correlated with average TDS in the fully adjusted models, while no effects from ethnicity and gender were detected. Low parental care partially reduced the association between FV and mental health, which could inspire research on parenting interventions and its possible developmental effect on children.

This study (2017) represents a novel look into the relationship between diet as a whole and depressive symptoms in the female Japanese population. 3963 young adults (18 years) and 3833 middle-aged (average age 47.9) took part in this experiment. Instead of the previously used Japanese Food Guide Spinning Top, dietary information was conveyed through a diet history questionnaire. Presence of depressive symptoms was determined using a Center for Epidemiologic Studies Depression (CES-D) score. 22% of young females and 16.8% of middle-aged women were deemed to express depressive signs. When the highest quintile of the generated diet quality score was compared to the lowest quintile after adjustment for potentially confounding factors, the odds risk (OR) of depressive symptoms for young adults and middle-aged women were 0.65 (p=0.0005) and 0.59 (p<0.0001) respectively. Sakai and his team (2017) concluded that incidence of depressive symptoms in both young and middle-aged women may be reduced through consuming a higher quality diet.

The hypothesis of this robust U.S. study was whether fruit and vegetable (FV) consumption during adolescence could be linked to an attenuation in risk of developing depression in adulthood. The 3696 participants of this cohort study were taken from the Add Health Study, and were aged 17 at baseline in 1994-1995, and then were 29 at follow-up taking place between 2007-2008. Depression was measured using Center for Epidemiologic Studies Depression Scale (CES-D), while a questionnaire was completed detailing which fruit and vegetable items were consumed the day before, to determine fruit and vegetable intake. The group with the highest percentage failure to consume fruits and vegetables the day before was those who were classed as depressed at baseline and at follow-up also on the CES-D (31% for fruit, 42% for vegetables). But the association between FV consumption and depression was weakened after repeating in fully adjusted models. Although there was promise of an existing link, further studies are required and the use of different dietary measures could produce more robust evidence.