This study chose to test the positive association between “healthy” diet consumption and reduced depressive symptoms by targeting young adults with elevated levels of depression symptoms and who do not eat healthily (first RCT to assess young adults). The 101 young adults were randomly categorised into either the diet group (who implemented a diet alteration for 3 weeks) or the control group (to consume their habitual diet) and were examined on symptoms of depression (using Centre for Epidemiological Studies Depression Scale (CESD-R); Depression Anxiety and Stress Scale– 21 depression subscale (DASS-21-D)), memory (through Hopkins Verbal Learning Test), current mood (Profile of Mood States) and self-efficacy (New General Self-Efficacy Scale) at baseline and after the intervention. Diet compliance was also determined through self-reported questionnaires and spectrophotometry. The results showed that the Diet group had reported significantly less symptoms of depression than the control group on the CESD-R (p=0.007) and DASS-21 depression subscale (p=0.002) while controlling for baselines scores on these scales. The lower DASS-21 depression scores were maintained 3 months later proven by follow up phone calls. These are promising signs for diet intervention to be utilised in the management of depression.

This 2020 systematic review analyses 20 different studies to break down the scientific evidence on the effectiveness of dietary habits as treatment strategies for depressive people. By conducting narrative synthesis, the following diets were found to aid in depression: fatty acid intake; fish consumption; the micronutrients folic acid and magnesium; diets of anti-inflammatory nature; lack of processed food. High adherence to the dietary recommendations are vital, as are healthcare professionals offering support and encouraging healthy diets. To define precise strategies in prevention and management, further research would be required by public health.

Jacka et. al (2018) shares her comments on the SMILES trial, which was the first randomised controlled study to experiment with improved diets for the treatment of depression. Molendijk, one of the main researchers for the study that healthy eating has a substantial positive effect on depression, acknowledges expectation bias and difficulty blinding may have contributed to the end-result. Expectation bias can occur in lifestyle intervention studies, which was noted in the article. A strong correlation between diet alterations and varying depression scores were observed in the study, and it was argued many studies published later have produced the same results, deeming inadequate blinding in the SMILES trial to be unlikely. Jacka proposes that the SMILES trial should be regarded as an important preliminary step in the field of nutritional psychology research.

Salari-Moghaddam and team (2019) explore the association between MIND diet adherence and risk of developing psychological disorders (first study at time of publishing). A total of 3176 adults undertook this cross-sectional study. To calculate MIND diet score, the participants’ dietary intake was used (taken from the validated dish-based 106-item semi-quantitative food frequency questionnaire (DS-FFQ) completed by the individuals). Depression and anxiety were determined by the use of the Iranian validated version of Hospital Anxiety and Depression Scale (HADS), and psychological stress was measured by the utilisation of General Health Questionnaires (GHQ). After accounting for possible confounders, the data showed that those in the highest quartile of the MIND diet score had lower incidence of depression (OR 0.68) and psychological distress (OR 0.72) when compared to the lowest quartile. Anxiety was not significantly associated with MIND diet. In gender-stratified analyses, females in the top MIND score quartile had lower odds of depression (OR 0.6) and psychological distress (OR 0.66) than those in the lowest quartile, which was not observed in the males. Adherence to the MIND diet was found to reduce risk of developing depression and psychological distress, although it could not be strongly linked with reducing anxiety.

Seeking for new preventative and treatment strategies for psychiatry, Altun and colleagues (2019) conducted a systematic review of the current evidence on the association between Mediterranean diet and depressive symptoms. Twenty observational studies and six intervention trials discovered in one of the computer databases Medline, Embase, PsychINFO, Scopus and Google Scholar were included. 85% of the observational studies and all six intervention trials supported the claim that the Mediterranean dietary pattern is inversely associated with depressive incidence. The lack of methodological disparity in the Med style diets studied restricted comparisons but this was overcome by specifying criteria and compressive appraisal of the data. This review incites global implementation of dietary changes in the treatment of depression, which would cut down costs, and produce fewer side effects, although there will be a need to define the recommendable Mediterranean diet and for further research (clinical trials included).

Since suboptimal intake of fruit and vegetables is becoming recognised as a risk factor for cardiovascular disease and cancer, the global burden attributed to it was estimated and its impact compared with that of other major risk factors for disease. Lock and her team (2005) found that total worldwide mortality attributable to low fruit and vegetable consumption could be up to 2.635 million deaths per year, and that increasing FV intake to 600g daily could reduce the disease burden by 1.8%, and lessen the burden of ischemic heart disease by 31% and ischaemic stroke by 19%. Its attribution to stomach, esophageal, lung and colorectal cancers were slightly less at 19%, 20%, 12% and 2% respectively. This study highlights the importance of increasing daily fruit and vegetable intake in lowering the risk of many non-communicable diseases, and calls for greater inclusion of these important risk factors in public health policies.

As the first to do so at time of publishing, Firth et. al (2019) conducts a systematic review and meta-analysis looking at the overall evidence for dietary interventions on improving symptoms of depression and anxiety. The 16 randomised controlled trials included (with data for 45,826 participants) were found to report changes in symptoms of depression and/or anxiety in clinical and non-clinical populations (all but one included was clinical). The effect sizes diet intervention had in comparison to the control groups were determined employing random-effects meta-analyses. Dietary interventions were discovered to reduce depressive symptoms (p=0.002), even when focusing on high-quality trials (p=0.002). The results were similar when compared with both inactive (p=0.038) and active controls (p=0.035). Other findings included female populations experienced greater beneficial effects in reducing their depression and anxiety, although no effect of dietary intervention was proven for anxiety. The meta-analysis/systematic review demonstrates dietary improvements possess potential in lowering depressive symptoms across the population.

The hypothesis of this 2019 Korean study was whether a higher diet quality score in 19-64 year olds would reflect a lower chance of showing depressive or anxiety symptoms and a higher QoL. The 1295 participants of the National Fitness Award Project were examined on their diet quality through the use of the recommended food score (RFS), while psychological health and quality of life (QoL) were assessed by the beck depression inventory (BDI), beck anxiety inventory (BAI), and the World Health Organisation QoL-Brief (WHOQoL-BREF). After adjusting the data for covariates, the results showed those without depression had a significantly higher RFS value than the participants with depression in both male and female populations. The highest tertile group of RFS were observed to have a lower incidence of depression (OR =0.51, CI = 0.32-0.81, p-trend = 0.0043) and a drop in risk of scoring a QoL below the median (OR=0.4, p<0.001), in comparison to the lowest tertile group. The data could not associate anxiety with RFS, however they suggest a better quality diet relates to lower depressive symptoms and higher quality of life in Korean adults.

A systematic review of observational studies analysing the relationship between fruit and vegetable (F&V) intake and mental health in adults. There were 61 studies included in the review, which were either found from Pubmed or Web of Science databases dated up to June 2019, or found through manual search in relation to the previously discovered studies. The studies included mainly centred around depression and depressive symptoms, but there were also some on general and mental well-being, quality of life, sleep quality, life satisfaction, flourishing, mood, self-efficacy, curiosity, creativity, optimism, self-esteem, stress, nervousness, happiness, anxiety, minor psychiatric disorders, distress, and attempted suicide. By adopting narrative synthesis analysis, the researchers noted a higher intake of F+V (and some of their subgroups like berries, citrus, green leafy vegetables) may lead to higher levels of optimism, self-efficacy, and less likelihood of experiencing psychological distress, depressive symptoms, ambiguity and cancer fatalism. Although the limitation of the disparity in methodologies and populations across these studies analysed were mentioned, Głąbska and colleagues (2020) conclude that there is a vast majority of studies that suggest fruits and vegetables, processed F+V products alike, have a positive effect on mental health.

This study focuses on consumption frequencies of the main food categories in an elderly Taiwanese population and how it relates to risk of developing new depression in the future (assessed after 4 years). Logistic regression analysis was performed, while also controlling for possible confounding factors. There were a total of 1609 participants of the age above 65. When controlling for demographic, socio-economic, lifestyle and health-related variables but not cognitive status, both fruits (OR=0.66, p=0.038) and vegetables (OR=0.38, p=0.021) were protective against new depression in 4 years time. The results altered slightly when controlling for cognitive status as well: only vegetables (OR=0.4, p=0.039) reduced incidence of depression. Greater intake of eggs almost had a significant impact in both regression models (p=0.087 and 0.069), while no significant evidence could be found linking meat/poultry, fish, seafood, dairy, legumes, grains and tea with reduction of future depression. These results suggest increasing frequency of vegetable consumption can protect elderly populations from developing first depressive symptoms.

Saghafian et. al (2018) state that due to contradictory evidence present, this observational study aims to investigate the relationship between fruit and vegetable intake and prevalence of depression, anxiety and psychological distress in Iranian adults. A 106-item food frequency questionnaire (FFQ), Iranian-validated version of Hospital Anxiety and Depression Scale (HADS), and General Health Questionnaire (GHQ) were used to assess dietary habits, anxiety and depression, and psychological distress, respectively on 3362 Iranian adults. The women in the top quintile for fruit consumption were seen to have lower odds of depression, anxiety, and psychological distress (57%, 50%, 60% respectively) compared with women in the lowest quintile. Vegetable consumption was significantly associated with lower odds of depression (OR=0.65) in women and with lower incidence of anxiety (OR 0.43) in men. After adjusting for potential confounders, similar trends were observed: Iranian women belonging to the highest quintile of fruit and vegetable intake benefit from significantly reduced odds of depression (OR=0.55) and psychological distress (OR=0.60) compared to females in lowest quintile; in men also higher levels of fruit and vegetables in the diet resulted in a drop in psychological distress (OR=0.42). To conclude what the study found, increased F+V consumption in Iranian women had a greater degree of beneficial influence than men as reduced psychological distress, anxiety and depression were seen, while eating more vegetables lowered the possibility of depression and anxiety in women and men, respectively. Likelihood of suffering depression and psychological distress was lowered in both sexes where higher quantities of fruit and vegetables were included in their diets.

This study examines 3172 Iranian adults in order to correlate adherence to the Mediterranean Diet (MeD) and prevalence of psychological disorders. Those aged 18-55 were included in this cohort, while their psychological health, psychological distress, dietary intake and adherence to the MeD were all assessed through the use of the Iranian validated version of the Hospital Anxiety and Depression Scale (HADS), General Health Questionnaire (GHQ), a validated food frequency questionnaire (FFQ), and Trichopoulou et. al method, respectively. Those subjects most adherent to the MeD had lower risk for depression (OR=0.60), anxiety (OR=0.61) and psychological distress (OR=0.60) compared to those subjects with the lowest adherence. When examining the components of the MeD, the study inversely associated high fruit and vegetable consumption with lower risk of depression, anxiety and psychological distress, while grains were positively associated with depression, anxiety and psychological distress.

Are dietary patterns differently associated with differentiated levels of mental health problems? Results from a large cross-sectional study among Iranian manufacturing employees

Let them eat fruit! The effect of fruit and vegetable consumption on psychological well-being in young adults: A randomized controlled trial

Does eating fruit and vegetables also reduce the longitudinal risk of depression and anxiety? A commentary on 'lettuce be happy'

A prospective analysis of dietary fiber intake and mental health quality of life in the Iowa Women's Health Study

Adherence to healthy dietary guidelines and future depressive symptoms: evidence for sex differentials in the Whitehall II study

Association of a priori dietary patterns with depressive symptoms: a harmonised meta-analysis of observational studies

Evolution of well-being and happiness after increases in consumption of fruit and vegetables

Adherence to Alternative Healthy Eating Index in relation to depression and anxiety in Iranian adults.

Diet-regulated anxiety

Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies

Fruit and vegetable consumption and risk of depression: accumulative evidence from an updated systematic review and meta-analysis of epidemiological studies

Dietary fiber intake and depressive symptoms in Japanese employees: the Furukawa Nutrition and Health Study

Dietary fiber and its associations with depression and inflammation

Fermented foods, neuroticism, and social anxiety: an interaction model

Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies

Diet quality in persons with and without depressive and anxiety disorders

Association of food groups with depression and anxiety disorders

Understanding nutrition, depression and mental illnesses

Relationship between motivation, adherence to diet, anxiety symptoms, depression symptoms and quality of life in individuals with celiac disease

Dietary flavonoid intake and risk of incident depression in midlife and older women

A high-fat diet promotes depression-like behavior in mice by suppressing hypothalamic PKA signaling (animal study)

Food patterns and the prevention of depression

Exploration of the association between dietary fiber intake and depressive symptoms in adults

Diet-derived fatty acids, brain inflammation, and mental Health

Diet quality in persons with and without depressive and anxiety disorders

Dietary polyphenol intake and depression: Results from the Mediterranean healthy eating, lifestyle and aging (meal) study

Association of Western and traditional diets with depression and anxiety in women

Diet quality and depression risk: A systematic review and dose-response meta-analysis of prospective studies

A Mediterranean-style dietary intervention supplemented with fish oil improves diet quality and mental health in people with depression: A randomized controlled trial (HELFIMED).

Prospective association between adherence to the Mediterranean diet and risk of depressive symptoms in the French SU.VI.MAX cohort

The impact of nutrition and intestinal microbiome on elderly depression—a systematic review

Systematic review/meta-analyses effects of regulating intestinal microbiota on anxiety symptoms: a systematic review

Diet quality in persons with and without depressive and anxiety disorders

Association of food groups with depression and anxiety disorders

Association between fruit/vegetable consumption and mental-health-related quality of life, major depression, and generalized anxiety disorder:a longitudinal study in Thailand

A Randomised Controlled Trial of Dietary Improvement for Adults With Major Depression (The 'SMILES' Trial)

Economic Evaluation of a Dietary Intervention for Adults With Major Depression (The "SMILES" Trial)

Diet-Regulated Anxiety

Evidence of Higher Oxidative Status in Depression and Anxiety

Nutritional factors, physical health and immigrant status are associated with anxiety disorders among middle-aged and older adults: findings from baseline data of the Canadian Longitudinal Study on Aging (CLSA)

The association between dietary pattern and depression in middle-aged Korean adults