Diet, depression, and anxiety

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.

This robust observational/cross-sectional study (2019) conducted on 2942 employees of one of the biggest Iranian industrial manufacturing companies, Esfahan Steel Company, aimed to classify the workers into subgroups representing varying levels of mental health profile, and to examine its correlation with dietary patterns. After evaluating the study population on psychological distress, anxiety and depression through the use of Hospital Anxiety and Depression Scale (HADS) and General Health Questionnaire (GHQ-12), the three main dietary patterns “western”, “healthy” and “traditional” were identified. Based on the factor mixture model, the vast majority of the population (91.2%) could be classed as ‘low mental health problems’, and the remaining 259 individuals as ‘high mental health problems’. The results suggested the employees who adhered to a more Western and traditional dietary pattern were more likely to be in the high mental health problems group, while those in the highest tertile of healthy dietary pattern showed lower odds in being classed as having high mental health problems. These findings could urge workplace health promotion policymakers to change their approach in improving mental health, and encourage further research into altering dietary habits and its effect on psychological well-being in employees.

As dietary fibre is linked with affecting depression via gut microbiome, Ramin and researchers (2020) investigated its association with mental health-related quality of life (QoL) scores, analysing the 14,129 postmenopausal women in the Iowa Women’s Health Study. Using a 127-item food frequency questionnaire in 1986 to assess dietary intake, the study followed up in 2004 with questionnaires consisting of a Mental Health (MH) component and a Mental Health Composite (MHC) scale to calculate mental health-related QoL scores. The median dietary fiber intake was found to be 19g per day, and ranged from 1.1g to 89.4g daily amongst the female population. The average MH score, after being adjusted for various factors such as age, alcohol consumption, physical activity, smoking status, education, energy intake, and waist-to-hip ratio, were discovered to be higher in those consuming larger quantities of fibre (P=0.02). When the data was adjusted for age and energy intake, the relationship between dietary fibre and MCS scores were observed to become insignificant. This 2020 study, being one of the first to link high fibre intake to increased future mental health-related QoL scores, further research is called for to supplement these discoveries.

Akbaraly and colleagues (2013) examine 4215 participants taken from the Whitehall II Study, on dietary pattern (using the Alternative Healthy Eating Index (AHEI)) and display of depressive symptoms at follow-up, to test the theory that adherence to a healthy diet may lead to less risk of developing depressive symptoms. In the occurrence that Centre for Epidemiological Studies Depression Scale score reached 16 or over, or antidepressant use was self-reported, the subject was defined to have recurrent depressive symptoms. The results showed that women who maintained high AHEI scores or improved their diet scores during the 10 years benefitted from a 65% and 68% reduction in risk of developing recurrent depressive signs later on, compared to those with consistently low AHEI scores. The inverse association between AHEI scores and recurrent depressive symptoms was only observed in the female population (OR=0.59; 95% CI 0.47-0.75, p<0.001). While examining AHEI components, it was found that vegetables, fruits, trans fat and ratio of polyunsaturated fat to saturated fat components were correlated to recurrent depressive symptoms in women. Poor diet is suggested to be a risk factor for future depression in women, which may spark a new aim for a public health campaign targeting women and depression.

Nicolaou and co. (2019) claim the evidence presented to date of varying dietary patterns having an impact on depression is inconsistent, therefore, this study looks at the association between dietary pattern and depressive symptoms in six cohorts undertaken in several different countries including Italy (INCHIATI), the Netherlands (LASA, NESDA, HELIUS), Australia (ALSWH) and the UK (Whitehall II). Cross-sectional data from 23,026 subjects were gathered in total, and findings meta-analysed. The cohorts with repeated measures of depressive symptoms at 5-6 years follow-up were used for the analysis of incidence (Whitehall II, InCHIANTI, ALSWH). Three a priori dietary patterns, Mediterranean Diet Score (MDS), Alternative Healthy Eating Index (AHEI-2010), and the Dietary Approaches to Stop Hypertension (DASH) diet were examined in relation to depressive symptoms. While at cohort-level the analyses were adjusted for confounders, meta-analysis used a random-effects model. This robust study identified the significant inverse association of the three dietary patterns with depressive symptoms (incidence of depression was significantly lower in those who scored higher MDS, AHEI-2010, and DASH), and provides further indication that adults who follow a healthy dietary pattern will reap the rewards with a lower risk of developing depressive symptoms, and experience fewer symptoms if depression is suffered.

In this 2016 study the relationship between adherence to healthy eating guidelines (measured by the Alternative Healthy Eating Index (AHEI-2010)) and depression was investigated in an Iranian population. Firstly, dietary information was taken from the 3363 cohort population using a 106-item semi-quantitative food frequency questionnaire (FFQ). Through the use of the Hospital Anxiety and Depression Scale (HADS) the prevalence of depression and anxiety were found to be 15.2% (males 10.8%, females 18.3%) and 30% (males 22.9%, females 35.1%) respectively. Those adults with higher adherence to healthy diets (top quartile of AHEI-2010) were 49% and 45% less likely to suffer from anxiety and depression than those in the bottom quartile, in the multivariate-adjusted model. When stratified analysis was employed, a variation in results between the two sexes were observed: while no significant association could be found in males, women in the highest categories of AHEI-2010 had an odds ratio of 0.51 for depression and anxiety. In the subpopulation aged 40 or less, the highly adherent individuals with regards to AHEI-2010 were 58% and 51% less likely to suffer from anxiety and depression than those less compliant. Adherence to healthy diets seems to be crucial in lowering the occurrence of depression and anxiety in Iranian adults.

This review focuses on the importance of diet on anxiety and anxiety-like behaviour, and inspects the current literature on how food components can influence anxiety at various stages of development, from gestation to adult life. Studies have established psychology, physiology and behaviour are interlinked, and that nutrition and anxiety can have both independent and interactive negative effects on health. The unbalancing of one of these factors can have a great impact on an individual, which may place a large importance on individual cognitive ability, diet and external environments. This review breaks down the available studies on how diet affects anxiety, highlighting limitations of the cohorts, and gaps in our understanding (namely food interactions and contemporary diets throughout the life course and at the physiological, metabolic psychological and emotional level), which could encourage future research into what Murphy and Mercer (2013) find to be lacking.

This 2019 systematic review of studies examining adherence to a healthy diet in relation to depressive symptoms or clinical depression, was designed to find an association between diet quality and depressive outcomes. Amongst the studies used were 20 longitudinal and 21 cross-sectional designed cohorts, employing an array of dietary measures including adherence to Mediterranean Diet assessments, the Healthy Eating Index (HEI) and Alternative HEI (AHEI), the Dietary Approaches to Stop Hypertension, and the Dietary Inflammatory Index. Encouraging evidence was observed especially for Mediterranean Diet and incident depression, as a combined relative risk estimate of highest against lowest adherence from 4 longitudinal studies was calculated to be 0.67 (95% CI 0.55-0.82). Furthermore, again in 4 longitudinal studies an association between lower dietary inflammatory index with a drop in risk of depression (RR 0.76). Additional longitudinal studies with other indices suggested the same trend in the inverse association between healthy diet and depression. This systematic review concluded adhering to a Mediterranean Diet and low inflammatory diet can offer protection against depression in observational studies.

This was a 2018 systematic review and meta-analysis of 27 publications associating fruit and vegetable (FV) intake and depression. 16 cross-sectional, 9 cohort and 2 case-control studies found in Medline/Pubmed, ISI, SCOPUS and Google Scholar until 2017 that focused on fruit, vegetable, and/or total FV intake in relation to depression were all included in this review. The pooled relative risk (RR) for depression in the highest vs lowest fruit consumption groups was 0.83 in cohort studies and 0.76 in cross-sectional studies. When consumption of vegetables was analysed the RR of depression was again lower in cohort studies (RR=0.86) and in cross-sectional designed studies (RR=0.80). A 20% lower incidence of depression was also seen when total FV consumption was analysed in cross-sectional studies. When meta-regression of the included observational studies was conducted, an inverse linear link between fruit or vegetable intake and incidence of depression (for every 100g of fruit consumed risk of depression decreased 3% in cohort studies; reduced chances of depression by 3% and 5% were also seen in cohort and cross-sectional studies respectively every 100g of fruit was eaten). These findings reinforce the recommendations of increasing fruit and vegetable intake to improve mental health.

This 2016 cross-sectional study investigated dietary intakes of soluble, insoluble, total and sources of fiber and their relationship with depressive symptoms in a Japanese adult population (19-69 years of age). A total of 1977 employees signed up for the experiment, which involved the uses of diet history questionnaires to assess dietary intake, and the Centre for Epidemiological Studies Depression Scale to report depressive symptoms. Fibre intake from fruits and vegetables was shown to significantly reduce depressive symptoms. The multi-variable adjusted odds ratio for the groups with lowest fruit and vegetable consumption attributes up to the highest were as follows: 1.00(reference), 0.80 (CI 0.6-1.05), and 0.65 (CI 0.45-0.95) respectively with p value for trend of 0.03. Although soluble, insoluble and total fibre in meals could not be associated with depression, this study demonstrates the preventative potential of greater fruit and vegetable intake in management of depressive symptoms.

This review explores the action of dietary fibers on inflammation and depression, and the poorly understood mechanism between the two, which includes looking at microbiota-driven modification of gene expression and increased neurotransmitter production as possibilities. Swann and her colleagues (2020) identify a possible mediatory effect of inflammation on the relationship between depression and fibre in the diet. By potentially altering the pH and permeability of the gut, a high-fibre diet may result in reduced inflammation and in turn decrease the collection of neurotransmitters and lessen the symptoms of depression. These encouraging findings could promote further research into the link between dietary fiber and depression and inflammation.

Hilimire, DeVylder and Forestell (2015) hypothesise fermented foods likely to contain probiotics may relate to neuroticism and social anxiety symptoms, given the established evidence for probiotics possessing an anxiolytic influence. Fermented foods intake, neuroticism and social anxiety were self-reported in this experiment of 710 young adults. An interaction model revealed neuroticism, exercise frequency, and fermented food consumption significantly and independently predicted social anxiety. Importantly, more frequent consumption of fermented foods in those high in neuroticism resulted in fewer symptoms of social anxiety. This study suggests fermented food products likely to contain probiotics may be an useful and cost-efficient way to prevent/manage anxiety symptoms especially in individuals with neuroticism tendencies.

The Netherlands Study of Depression and Anxiety was used in this 2018 study and the data from its 1634 adults at the 9-year follow up was extracted to explore the association of depressive and anxiety disorders and their subtypes (disorder type, severity, chronicity, clinical) with diet quality. Composite International Diagnostic Interviews were conducted to identify depression and anxiety disorders, while severity of the disorders were gauged through the uses of Inventory of Depressive Symptomatology (IDS), Beck Anxiety Inventory and Fear Questionnaire. Diet quality was assessed with the Mediterranean Diet Score (MDS) and Alternative Healthy Eating Index (AHEI), while chronicity was measured with life-chart interviews. Compared to the healthy control group, those participants with a current disorder were seen to have significantly poorer diets. When the subject population was further subdivided, it was evident that the lowest diet quality scores were observed in those with concurrent depressive and anxiety disorders. In fact, greater chronic depression or anxiety disorders and increased severity in the whole test population showed a dose-response association with lower quality dietary intakes. As poorer diet quality was linked to the presence of depressive and anxiety disorders as well as severity and chronicity of symptoms, further research into this relationship and whether enhancing diet quality could positively affect mental health may be warranted.

To explore which component of the Mediterranean diet can be attributed to the association between adherence to this diet and fewer depressive symptoms, Gibson-Smith and her team of researchers (2020) analyse the food groups of the Mediterranean Diet Score (MDS) independently and in combinations, and explore their relationships with severity and diagnosis of depression and anxiety. Data from 1634 subjects from the Netherlands Study of Depression and Anxiety was extracted for this cohort, documenting also information on food groups consumed from the food frequency questionnaire. Regression analysis was then performed using the incidence of depressive and anxiety disorders (established using Composite International Diagnostic Interview) and disease severity (measured with the Inventory of Depressive Symptomatology, Beck Anxiety Inventory, and the Fear Questionnaire). A total of 12 food groups were looked at based on those in the MDS, including alcohol consumption. The severity of depression and anxiety lessened as higher levels of non-refined grains and vegetables were consumed while the inverse association was seen within the non-drinkers. Those non-drinkers were also at greater risk of current depression/anxiety disorders compared to the control population, while those on more non-refined grain enriched diets had favourable odds. Higher fruit and vegetable consumption was linked to lower fear severity. It is indicated in the study that non-refined grains, vegetables and alcohol intake may play influential roles in the positive association between MDS scores, and depression and anxiety, which in turn signifies supplementary studies may be required to test the protective function of non-refined grains and vegetables in depression and anxiety.

While there is significant evidence for a link between metabolic conditions (including obesity and diabetes) with neuropsychiatric disorders, the mechanisms of pathogenesis involving the relationship between these conditions can be difficult to decipher. Melo et. al (2019) review the current research examining the relationship between neuropsychiatric disorders and diet-related nutritional imbalance, with a particular eye on the mechanisms of inflammation that are activated by dietary fatty acid intake (refined fats and sugars) in the diet. The authors note this is a particularly relevant area of study due to the significant changes in societal eating patterns towards a Western-style diet (i.e., high in processed fats and sugars). In this review, the authors discuss the mechanisms by which dietary fatty acids signal inflammatory processes that lead to neuroinflammatory conditions.

Sangsefidi et. al (2020) extracted data from 9965 adults from the population-based cohort study - the Yazd Health Study (YaHS) conducted during 2014 to 2016, to assess the association between dietary intakes and psychiatric disorders in Iran. Psychological and physical activity assessments were carried out using depression, anxiety and stress scale questionnaire (DASS 21 items) while a validated researcher-made questionnaire and anthropometric measurements were used to collect information on socio-demographic characteristics, tobacco use, history of chronic disease, and dietary assessment. The results included positive association between fish consumption and depression (OR=1.54) and inverse associations between vegetable intake with anxiety (OR=0.74) and stress (OR=0.59). Moreover eggs, fruits, milk and yoghurt were found to exhibit protective effects against depression and anxiety, while a drop in incidence of stress was linked to fruits and milk intake. Additional studies will be required to confirm these promising associations which could be used in future health promotion programs.

The authors start by exploring the relatively unknown connection between nutrition and depression, in which nutrition can play a key role in the onset, severity and duration of depression. The most well known eating patterns indicative of depression such as poor appetite, skipping meals, and a strong desire for sweet foods, also occur in the lead up to depression. Rao et. al (2008) write about nutritional neuroscience and aim to shed light on the relationships that exist between nutritional factors and human cognition, behavior and emotions.

The aim of this (2016) study was to examine the associations between regular intake of dietary flavonoids with depression risk. Chang and colleagues studied 82,643 adult women without previous history of depression at baseline in this study (Depression was defined as physician- or clinician-diagnosed depression or antidepressant use). A total of 10,752 cases of depression occurred during a 10 year follow-up. The study revealed that flavonoids, including flavonol, flavone, and flavanone, were inversely associated with depression risk. In flavonoid-rich food-based analyses, the HR was 0.82 among participants who consumed ≥2 servings citrus fruit or juices/d compared with <1 serving>

This 2019 study aimed to investigate whether obesity is a causative factor for the development of depression and uncover the molecular pathway(s) that link these two disorders. A mechanism in which exposure to a high-fat diet (HFD) in mice could be linked to changes in hypothalamic function (that leads to depression) was identified - the findings suggested that dietary intake of saturated fats disrupts function of the hypothalamus by suppressing cAMP/PKA signalling through activation of phosphodiesterase 4A (PDE4A). Free fatty acid receptor 1 (FFAR1) inhibition and/or increase of cAMP signaling in the hypothalamus could offer potential therapeutic targets to counteract the effects of dietary or genetically induced obesity on depression.

Martínez-González and Sánchez-Villegas (2016) review the evidence on the association between several food patterns with reduced depression risk that seems to be consistent across countries, cultures and populations according to several systematic reviews and meta-analyses of observational studies. Of all the food patterns thought to be effective in lowering future risk of depression (including the Alternative Healthy Eating Index, the Prudent diet or the Provegetarian Food Pattern) only the Mediterranean Food Pattern has been tested for primary prevention in a large randomised trial (inverse association was not statistically significant). According to large and well-conducted observational studies, food patterns potentially associated with reduced risk of depression are those emphasising seafood, vegetables, fruits and nuts. With some guidelines concluding that the evidence is limited, the authors express the need for further exploration into how different micro- and macro-nutrients incorporation into diet can potentially influence depressive risk since the shape of the dose-response curve and the potential existence of a nonlinear threshold effect have not yet been established.

This 2018 cross-sectional study assessed 16,807 adults (aged 20 years and over) on dietary consumption (obtained through two 24-hr dietary recall interviews) and depressive symptoms (using Patient Health Questionnaire) with the aim of exploring the association between dietary fibre intake and the risk of developing depression. Results showed that dietary intakes of total, cereal, vegetable, and fruit fibre were inversely associated with depressive symptoms in unadjusted model and multivariate-adjusted model 1. Also, in multivariate-adjusted model 2, when the highest quintile was compared to the lowest quintile with respect to total, cereal, vegetable, and fruit fibre intakes, the odds ratios of depressive symptoms were 0.59, 0.90, 0.58 and 0.64, respectively. While dose-responses analyses revealed the non-linear association between total fibre consumption and depression risk, the relationships with cereal, vegetable and fruit fibre intake were found to be linear. While further larger prospective studies are required to confirm these findings, Xu et. al (2018) and their results suggest inverse associations between consumption of total fibre, vegetable fibre and fruit fibre with depressive symptoms.

Godos and her colleagues (2018) studied 1,572 adults living in Southern Italy aiming to assess the association between habitual dietary intake of total polyphenols, their classes, subclasses, and individual compounds with depressive symptoms among participants of the Mediterranean healthy Eating, Lifestyle and Ageing (MEAL) study. Food frequency questionnaires, Phenol-Explorer, and the Center for Epidemiological Studies Depression Scale (CES-D-10) were used to calculate habitual polyphenol consumption and to screen for depressive symptoms, respectively. Based on the total of 509 participants who reported depressive symptoms, total polyphenol intake could not be associated with depressive symptoms. Following adjustment for potential compounding factors, dietary intake of phenolic acid (OR = 0.64), flavanones (OR = 0.54), and anthocyanins (OR = 0.61) showed significant inverse association with depressive symptoms, when comparing the highest with the lowest quartile. Furthermore, the associations with anthocyanins and flavanones were in a dose-response manner. Other findings included inverse associations between depressive symptoms with quercetin, naringenin, and consumption of citrus fruit and wine, when comparing the highest to lowest quartiles. Although further studies are required to affirm these observed relationships, greater dietary intake of flavonoids may be inversely associated with depressive symptoms.

Through the use of food frequency questionnaires and factor analysis (to determine habitual dietary pattern), General Health Questionnaire (GHQ-12 [to measure psychological symptoms]) and a structured clinical interview (to assess depressive and anxiety disorders), Jacka et. al (2010) examined the extent to which the high-prevalence mental disorders are related to habitual diet in 1,046 women aged 20-93 years randomly selected from the population. After making adjustments in the factor analysis for age, socioeconomic status, education and health behaviors, a "western" diet of processed or fried foods, refined grains, sugary products, and beer was discovered to be associated with a higher GHQ-12 score, while a “traditional” dietary habit (composed of vegetables, fruit, meat, fish and whole grains) was linked to lower risk of developing major depression or dysthymia (persistent depression) and for anxiety disorders. There was also an inverse association between diet quality score and GHQ-12 score that was not confounded by age, socioeconomic status, education, or other health behaviors. Although these findings demonstrated an association between habitual diet quality and the high-prevalence mental disorders, additional prospective studies are warranted to confirm these relationships.

Molendijk and his team (2018) pooled data from 24 independent cohorts (totalling 1,959,217 person-years) to investigate the link between diet quality and incidence of depressive disorders. Although adherence to low quality diets and food groups could not be associated with higher depression incidence, consistently consuming a high-quality diet, regardless of whether it is healthy/prudent or Mediterranean, was linked with a reduced risk of depression over time (odds ratios ranged 0.64-0.78 in a linear dose-response fashion [p<0.01]). Lower incidence of depressive symptoms was also found to be linked to a relatively low dietary inflammatory index (OR=0.81), and consumption of fish and vegetables (odds ratio 0.86 and 0.82 respectively). Although not all the available results are consistent with the hypothesis that diet influences depression risk, this study provides evidence that a higher diet quality is associated with a drop in risk for the onset of depressive symptoms. Molendijk and colleagues (2018) call for more prospective studies that control for confounders such as obesity incidence and for supplementary randomised controlled prevention trials to further validate these findings.

This 2019 study investigated whether a Mediterranean-style diet (MedDiet) supplemented with fish oil can improve mental health in adults already suffering from depression (152 adults aged 18-65). Those who had self-reported depression were randomly given either: fortnightly food hampers and MedDiet cooking workshops for 3 months and fish oil supplements for 6 months; or attend social groups every 2 weeks for 3 months. Out of the 95 who completed 3 months, the MedDiet group secured a higher MedDiet score, consumed more vegetables, fruits, nuts, legumes, wholegrains, greater variety in vegetables, less unhealthy snacks and red meat/chicken (all of these p-values were below 0.05, signifying statistical significance). With regards to depression, the MedDiet group reported more reduction in depression and enhanced mental health QoL scores at the 3-month point. This improvement in mental health and diet were sustained for 6 months. There was a correlation identified between a drop in depression with greater MedDiet scores, increased consumption of nuts and more diversity in vegetables, while higher levels of omega-3 and decreased omega-6 were linked with improved mental health. Other mental health improvements had similar correlations, most notably for increased vegetable diversity and legumes. Parletta et. al believe this is one of the first randomised controlled trials to demonstrate healthy dietary changes are achievable and when supplemented with fish oils, can improve mental health in people with depression.

This robust French study (2018) examined whether adherence to the Mediterranean Diet (MD) was associated with incident depressive symptoms. The 3523 participants taken from the SU.VI.MAX cohort had at least three dietary records at baseline during the first 2 years of follow-up, were free of depression at the start of the study, and had Centre for Epidemiological Studies Depression Scale (CES-D) data at the end of the follow up. Incident depressive symptoms (defined by CES-D score ≥17 for men and ≥23 for women) were seen in 172 individuals during the follow-up and were found to be associated with adherence to the rMED score in men (OR=0.91, p=0.03) after adjustments for potential confounders were made. This current study provided additional scientific evidence for the benefits of Mediterranean diet on health, with findings indicating higher adherence to the Mediterranean Diet at midlife were associated with a fewer incidental cases of depressive symptoms especially among men, although data for women need further investigating.

Following evidence that gut microbiota can regulate brain function and that dysbiosis (imbalance of microbiota) in the intestines was related to anxiety, Yang and others (2019) compiled evidence for the improvement of anxiety symptoms through regulation of intestinal microbiota in the form of a systematic review. Of the 3334 articles retrieved initially, 21 studies including 1503 subjects were included in this review following quality evaluation. 15 studies chose probiotics as interventions to regulate microbiota while the other 6 involved non-probiotic ways such as adjusting daily diets. In the studies that used treatment as usual plus interventions regulating intestinal flora (IRIF) as interventions, two out of the five studies were found to be effective and used non-probiotic means of intervention (40% success rate) while 56% of the studies that used IRIF alone improved anxiety symptoms. When analysed further, those studies conducting non-probiotic interventions were 80% effective while 45% of studies that supplemented their subjects with probiotics were found to help with anxiety symptoms. To summarize, 11 out of the 21 studies (52%) included in this review were effective in reducing anxietal signs (5 using probiotic and 6 using non-probiotic interventions). Furthermore, the researchers observed 86% of the studies (6 out of 7) indicating that regulation of intestinal microbiota could treat anxiety symptoms. Although meta-analysis results are not available and more studies are warranted to confirm these findings, Yang et. al (2019) highlight that more than half of the studies demonstrated the positive effects of regulating intestinal microbiota in the treatment of anxiety symptoms and the higher efficacy of non-probiotic interventions compared to probiotics.

Pengpid & Peltzer (2019) collected data from 442 temple members with prehypertension and/or prediabetes (randomly selected from 12 Buddhist temples in Nakhon Pathom province in Thailand) to investigate the effect of fruit and vegetable consumption on mental health-related quality of life (QoL), major depressive disorder and generalised anxiety disorders. In this longitudinal study, frequent vegetable consumption was in the fully adjusted model associated with better mental health-related quality of life (p=0.027) while frequent fruit consumption was not linked with a higher QoL. However in the unadjusted model fruit and vegetable consumption was related to greater mental health-related QoL (p=0.033). In addition, more frequent fruit, vegetable, fruit and vegetable consumption did not significantly reduce the risk of major depressive and generalised anxiety disorder. To conclude, although there was no evidence found linking frequent fruit and vegetable consumption with better mental health-related quality of life, regularly eating vegetables was associated with a better QoL.

Jacka et. al (2017) designed this 12 week, single blind, randomised controlled trial to investigate the efficacy of a dietary improvement program for the treatment of major depressive episodes. The intervention consisted of seven individual nutritional consulting sessions delivered by a clinical dietician and the control condition comprised a social support protocol to the same visit schedule and length. Of the 67 individuals who enrolled for this trial (33 = diet intervention, 34 = control), 55 participants were using some form of therapy; 21 using psychotherapy and pharmacotherapy combined; 9 were on psychotherapy alone; and 25 were exclusively using pharmacotherapy. With 31 from the diet support group and 25 in the social support group with complete data at 12 weeks, it was found that the dietary support group significantly improved MADRS (assesses depression symptomatology) between baseline and 12 weeks compared to the social support group (p<0.001). Remission, defined as a MADRS score <10, was achieved for 32.3% (n = 10) and 8.0% (n = 2) of the intervention and control groups respectively; number needed to treat (NNT) based on remission scores was 4.1 (95% CI of NNT 2.3-27.8); and a sensitivity analysis was utilised to discover that the impact of the intervention was robust to violations of MAR assumptions. Jacka and co (2017) believe these results demonstrate that improvements made to diets may be an efficacious and accessible treatment option for major depression and also could be beneficial for common comorbidities.

Chatterton and her colleagues (2018) collected data from and evaluated the cost-effectiveness of the SMILES trial, which demonstrated the efficacy of dietary improvement since a significant improvement in Montgomery-Asberg Depression Rating Scale scores was seen in the diet support group compared to a control group over 12 weeks. The trial involved participants being randomised into either seven sessions with a dietician for dietary support or an intensity matched social support (befriending) control condition. Evaluating the costs from health sector and societal perspectives, data on food and travel costs, medications, medical services, workplace absenteeism and presenteeism were collected using a resource-use questionnaire. Standard Australian unit costs for 2013/2014 were applied and incremental cost-effectiveness ratios (ICERs) were calculated as the difference in average costs between groups divided by the difference in average Quality Adjusted Life Years (QALY, the primary outcome of the SMILES trial). Compared with the social support condition, average total health sector costs were $856 lower and average societal costs were $2591 lower for those receiving dietary support. These differences were driven by lower costs arising from fewer allied and other health professional visits and lower costs of unpaid productivity. Although significant differences in mean QALYs were not found between groups, 68% and 69% of bootstrap iterations showed the dietary support intervention was dominant, meaning additional QALYs at a cheaper price, from the healthcare sector and societal perspectives. Therefore Chatterton and researchers (2018) found the dietary support intervention likely to be cost-effective as an adjunctive treatment for depression.

This 2014 paper measured the urinary redox potential of urine, which is a simple method for evaluating antioxidative status, with the aim to analyse the global antioxidative status and to correlate these findings with measures of anxiety and depression in 63 individuals (28 male, 35 females, ages 20-65). Normal anxiety state values corresponded to low urine redox potentials whereas higher anxiety states were associated with high urinary redox potential indicating high oxidative stress. It was also found that those with normal values in terms of the validated Beck Depression Inventory (BDI) questionnaire (used to assess anxiety and depression) had significantly lower urine redox potentials than individuals with higher BDI values. The results suggest that individuals with depression and anxiety are deficient in antioxidants, indicative of oxidative stress.

This 2020 study compared the lifetime prevalence of anxiety disorders among foreign-born and Canadian-born adults in middle and later life using data from the Canadian Longitudinal Study on Ageing (2010-2015). Of the 26,991 participants (49.3% men, 82.5% Canadian born, 58.5% aged 45–65 years) the overall prevalence of self-reported physician diagnosis of anxiety disorders was 8.5%, with immigrants being lower than Canadian-born respondents (6.4% vs. 9.3%, p < 0.001). After accounting for socio-economic, health-related and nutritional covariates, the adjusted odds ratio (aOR) for anxiety disorders was lower among immigrants compared to those who were Canadian-born. The risk factors were identified as: younger age (aORs = 1.79–3.52), being a woman (aOR=1.25), single status (aOR=1.27), lower income (aOR = 1.28–2.68), multi-morbidities (aORs = 2.73–5.13), chronic pain (aOR = 1.31), lifetime smoking ≥ 100 cigarettes (aOR=1.35), BMI<18.5 (aOR=1.87), body fat ≥ 26% (aORs = 1.28–1.79), consuming <3 types of fruit and vegetable (aors = 1.24–1.26), pastry consumption>1/day (aOR = 1.55). The paper states that targeting socio-economic and nutritional risk factors may reduce the burden of anxiety disorders in middle and late adulthood.

Park, Kim and Lee (2019) selected participants from a subset of the Korean Genome and Epidemiology Study to take part in this study investigating the association between dietary patterns and depression in middle-aged Koreans. Utilising the Korean version of the Beck Depression Inventory participants who scored higher than or equal to 16 were defined as having depression, while the subjects’ food intake over the year was determined by the use of a validated semi-quantitative food frequency questionnaire. 448 of the 3388 participants in the study (13.2%) were identified as having depression. High consumption of vegetables, soybeans, mushrooms, seaweeds, white fish, shellfish, fruits and a low intake of white rice were characterised as the “healthy” dietary pattern, while the “unhealthy” dietary pattern was identified by high intakes of white rice, meats, ramen, noodles, bread, coffee and low consumption of rice with other grains. After adjusting for potential confounders, the subjects in the highest quartiles of the healthy dietary pattern had a significantly lower odds ratio (OR=0.59, p = 0.0037) than those in the lowest quartiles. As well as this, the unhealthy dietary pattern was found to be negatively associated with depression (OR=1.65, p = 0.0021) among Korean adults. The study concluded that a healthy dietary pattern rich in mushrooms, soybeans, seaweeds, white fish, shellfish, vegetables, fruits) is associated with lower risk of depression while an unhealthy diet composed of ramen, meats, noodles, rice, bread and coffee is linked to the inverse.

This 2013 review summarises the animal- and human-based studies on the relationship between diet, exercise and sleep (three significant mediators in the development, progression and treatment of depression) with major depressive disorder, and their influence on dysregulated pathways associated with depression such as neurotransmitter processes, immuno-inflammatory pathways, hypothalamic-pituitary-adrenal (HPA) axis disturbances, oxidative stress and antioxidant defence systems, neuroprogression, and mitochondrial disturbances. The authors call for more studies and mental health interventions on these aforementioned lifestyle factors associated with depression (including their effects on physiological processes) in order to expand our understanding and treatment of major depressive disorder.

This 2017 cross-sectional study assessed 3846 general public adults in Isfahan, Iran to investigate the association between adherence to DASH-style diet and psychological health. A DASH score was created focusing on 8 components (namely fruits, vegetables, nuts, legumes, dairy products, grains, sweetened beverages and sweets, sodium, and red and processed meats) to classify the participants into 3 categories: [low (≤40), moderate (41-50), and high adherence (≥51)]. Iranians with moderate adherence to the DASH diet were discovered to be associated with lower odds of depression (OR = 0.73, p = 0.63) compared with those with low adherence and this link was significant in the stratified analyses for women and for normal-weight subjects. After controlling for potential confounders, inverse associations were observed between high adherence and anxiety in normal-weight individuals, and also between moderate adherence to the DASH diet and anxiety in those overweight or obese. A significant association could not be found between consumption of the DASH-style diet and psychological stress. Valipour et. al (2017) admit further studies are required to confirm the inverse association between moderate adherence to DASH dietary pattern and depression.

This 2019 observational study compared the diets of depression sufferers and those individuals without any depressive levels to assess the relationship of intakes of various food groups with depression. The food groups data the researchers took from the participants included legumes, nuts, whole-grain foods, chocolates, sweet foods, refined sugars and vegetables and fruits. The diet of depressed individuals in this study had significantly lower levels of legumes, fruits, and vegetables but consisted of more sweets and refined sugars (p<0.05 for all comparisons). After adjustments were made for age and sex, depression was significantly associated with: no consumption of legumes (adjusted odds ratio [aOR] = 2.60); low intake of fruits and vegetables (aOR= 2.69); and high consumption of sweet foods and refined sugars (aOR = 1.91). Although Grases and colleagues (2019) note that conclusions cannot be drawn in terms of causality in this study and further research is required to check the causal relationships of the consumption of specific food groups with depression, and vice versa, this current study demonstrated subjects without depression consumed more legumes, fruits and vegetables and had fewer sweets and pastries in their diets than those with depression.

Shafiee and others (2018) produced a large population-based, cross-sectional study examining the association between depression/anxiety symptoms with serum pro-oxidant-antioxidant balance (PAB) in 7516 adults (62% female; 38% male; age 35-65). This aim is due to the fact that depression and anxiety are significantly associated with inflammation, while inflammatory-related conditions are related to oxidative stress resulting from a disturbance in PAB. Serum PAB values increased incrementally across the four groups (no or minimal, mild, moderate and severe depression) in both men and women (Ptrend < 0.001 among men and Ptrend = 0.005 among women). Analysing the data regarding anxiety, serum PAB values increased significantly across the four groups in men (Ptrend = 0.02) but not in women (Ptrend = 0.2). The adjusted odds ratios for serum PAB values among men with severe depression and anxiety symptoms were 1.75 and 1.27, respectively while those among women were 1.40 and 1.17, respectively. It appears that depression and anxiety symptoms are associated with higher degrees of oxidative stress, expressed by greater serum PAB values.

Su et. al (2018) aimed to provide the first systematic review/meta analysis at the time of researching to evaluate the association of anxiety symptoms with omega-3 polyunsaturated fatty acids (PUFAs). After searching for clinical trials assessing the anxiolytic effect of omega-3 PUFAs in humans (placebo-controlled and non-placebo) on numerous online databases, data on 1203 participants with omega-3 PUFA treatment (mean age, 43.7 years; mean female proportion, 55.0%; mean omega-3 PUFA dosage, 1605.7 mg/d) and 1037 participants without omega-3 PUFA treatment (mean age, 40.6 years; mean female proportion, 55.0%) were gathered. An association was observed between clinical anxiety symptoms with omega-3 PUFA treatment compared with control arms, with subgroup analysis showing that the association of treatment with reduced anxiety symptoms was significantly greater in subgroups with specific clinical diagnoses than in subgroups without clinical conditions. The anxiolytic effect of omega-3 PUFAs was significantly better than that of controls only in subgroups with a higher dosage (at least 2000 mg/d) and not in subgroups with a lower dosage (<2000 mg>

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Association between macronutrients intake and depression in the United States and South Korea

Bidirectional associations between food groups and depressive symptoms: longitudinal findings from the Invecchiare in Chianti (InCHIANTI) study

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Dietary seaweed intake and depressive symptoms in Japanese adults: a prospective cohort study

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