Food and Mental Health

What is nutritional psychiatry?

Nutritional psychiatry is a relatively new field of research that investigates the relationship between dietary patterns, specific nutrients, and mental health outcomes. It draws on epidemiology (population studies), neuroscience (understanding brain chemistry and structure), gut microbiome research, and clinical trials.

The field emerged partly from a puzzling observation: as diets in Western countries became more reliant on ultra-processed foods and less reliant on whole foods, rates of depression and anxiety increased, even as many other health interventions improved. This correlation alone proves nothing, but it prompted researchers to investigate whether the relationship was causal.

The principal figures in the field include Professor Felice Jacka at Deakin University's Food and Mood Centre in Australia, who led the SMILES trial and co-founded the International Society for Nutritional Psychiatry Research (ISNPR). The field now has its own peer-reviewed journals, major research centres, and a growing evidence base that is beginning to influence clinical guidelines in several countries.

The current state of evidence

The conclusion from researchers in the field: diet quality appears to be a modifiable risk factor for mental illness, in the same way that physical inactivity and smoking are modifiable risk factors for cardiovascular disease. Not a single cause, not a guaranteed treatment, but a meaningful and actionable contributor.

The evidence from population studies

Large epidemiological studies have consistently found associations between diet quality and mental health outcomes.

Higher diet quality, lower depression risk

A meta-analysis cited in the SMILES trial paper found that higher adherence to a Mediterranean diet was associated with a 30% reduced risk of depression, with no evidence of publication bias. A separate meta-analysis found that a dietary pattern characterised by higher intakes of fruit, vegetables, fish, and whole grains was associated with a reduced likelihood of depression in adults.

Ultra-processed food and mental health: convincing evidence

The 2024 BMJ umbrella review (Lane et al.), the most comprehensive synthesis of UPF and health outcomes, covering almost 10 million people across 45 meta-analyses, found:

• Convincing evidence (the highest classification) that higher UPF consumption was associated with a 48 to 53% higher risk of anxiety and common mental disorder outcomes.
• Highly suggestive evidence that higher UPF consumption was associated with a 22% higher risk of incident depression in prospective studies.

These are the same evidence grades that UPF received for cardiovascular disease mortality and type 2 diabetes, placing mental health alongside the most established physical health harms. A separate meta-analysis of 17 studies (385,541 participants) on UPF and mental disorders specifically found that higher UPF consumption was cross-sectionally associated with a 44% higher odds of depressive symptoms and 48% higher odds of anxiety symptoms. See the UPF guide for the broader picture.

UK data: the English Longitudinal Study of Ageing (ELSA)

A 2025 prospective study using ELSA data examined dietary risk factors for depression and anxiety over a 3.5-year follow-up in middle-to-late adulthood in England. It identified specific dietary patterns prospectively associated with the development of both depression and anxiety, adding to the evidence that this is not simply reverse causation (the theory that people eat worse because they are depressed, rather than becoming depressed because they eat worse).

UK Biobank: the EAT-Lancet diet and mental health (2024)

A 2024 study in Nature Communications examining 180,446 UK Biobank participants found that adherence to the EAT-Lancet reference diet (a whole food, predominantly plant-based dietary pattern) was prospectively associated with lower incidence of depression, anxiety, and their co-occurrence.

Is this just reverse causation?

The most common challenge to this evidence is that people who are depressed or anxious may eat worse diets, meaning the dietary pattern is a consequence of poor mental health, not a cause. The research community takes this seriously. However:

• Prospective studies that measure diet before mental health outcomes develop, and find the association holds, are harder to explain by reverse causation alone
• The associations are found even after controlling for baseline mental health symptoms
• The biological mechanisms (next section) provide plausible pathways for causation in the diet-to-mental health direction
• The SMILES trial provides direct experimental evidence that improving diet improves mental health

The current scientific consensus is that the relationship is bidirectional, but there is credible evidence for the diet-to-mental health direction that cannot be explained by reverse causation alone.

How diet influences brain function. The mechanisms

Multiple biological pathways link dietary patterns to brain chemistry and mental health. None operates in isolation. They interact and reinforce each other.

The gut-brain axis

Around 90% of the body's serotonin is produced in the gut. The gut microbiome influences serotonin synthesis, dopamine activity, and the production of short-chain fatty acids (SCFAs) that communicate with the brain via the vagus nerve. A diet rich in diverse plant fibres supports a diverse, healthy microbiome; a diet dominated by ultra-processed food reduces diversity and can promote gut barrier dysfunction and systemic inflammation that reaches the brain. This is covered in depth in the gut health guide. In summary: what you feed your gut bacteria influences the chemistry of your brain.

Neuroinflammation

Chronic low-grade systemic inflammation (driven by poor diet, ultra-processed food, excess sugar, sedentary behaviour, and stress) can cross into the brain and produce neuroinflammation. Neuroinflammation is increasingly understood to be a significant mechanism in depression. Anti-inflammatory dietary patterns (particularly the Mediterranean diet, rich in polyphenols, omega-3 fatty acids, and fibre) reduce systemic inflammation markers and may reduce neuroinflammation.

Omega-3 fatty acids and neuroplasticity

DHA (docosahexaenoic acid) makes up approximately 20% of the fat content of the brain and is structurally essential for neuronal membrane integrity, neurotransmitter signalling, and synaptic plasticity. EPA (eicosapentaenoic acid) has potent anti-inflammatory properties that influence brain function. Both are found primarily in oily fish (salmon, mackerel, sardines, herring, trout) and in smaller amounts in walnuts and flaxseeds. Plant-derived ALA converts to EPA and DHA only inefficiently in the body.

People with depression have consistently been found to have lower blood levels of EPA and DHA than non-depressed individuals. Meta-analyses of omega-3 supplementation trials show modest but consistent reductions in depressive symptoms, with EPA-enriched formulations showing stronger effects. The most convincing evidence from population data is that low oily fish consumption is associated with higher depression rates across different countries and populations.

Blood glucose stability and mood

High-sugar, low-fibre diets cause rapid spikes and subsequent crashes in blood glucose. These fluctuations directly influence mood, energy, and cognitive function. The sharp fall in blood glucose after a high-sugar meal can produce irritability, anxiety, fatigue, and difficulty concentrating. Whole foods, particularly those rich in fibre and with a low glycaemic index, produce slow, stable blood glucose responses that avoid these fluctuations and provide sustained mental energy. See sugar and free sugars for the broader picture.

Tryptophan, serotonin, and dietary precursors

Serotonin is synthesised from the essential amino acid tryptophan, which must be obtained from food. Tryptophan competes with other large neutral amino acids to cross the blood-brain barrier, so the ratio of tryptophan to competing amino acids in the blood determines how much reaches the brain for serotonin production. Interestingly, a moderate carbohydrate intake can increase this ratio, because insulin causes competing amino acids to be taken up by muscle, leaving tryptophan relatively more available. This is one proposed explanation for carbohydrate cravings during low mood, and why extremely low-carbohydrate diets can sometimes worsen mood in susceptible individuals.

Foods rich in tryptophan: eggs, turkey, chicken, dairy, oats, pumpkin seeds, and legumes. Serotonin synthesis also requires cofactors including vitamin B6, iron, and vitamin C. Folate (B9) and vitamin B12 are required for neurotransmitter methylation pathways.

Key micronutrients

• Vitamin D. Widely deficient in the UK due to limited sun exposure (the skin cannot synthesise it from October to April). Vitamin D receptors are found throughout the brain; deficiency is consistently associated with higher rates of depression and seasonal affective disorder. The NHS recommends 10 micrograms per day in autumn and winter for everyone in the UK.
• Magnesium. Involved in over 300 enzymatic reactions, including those in serotonin and dopamine synthesis. Low intake is associated with depression and anxiety. Found in leafy greens, nuts, seeds, whole grains, and legumes.
• Folate (B9). Required for serotonin and dopamine synthesis and DNA methylation in the brain. Low folate status is consistently associated with depression. Found in dark leafy vegetables, legumes, fortified cereals, and eggs.
• Vitamin B12. Deficiency leads to impaired neurotransmitter synthesis and is associated with depression, fatigue, and cognitive decline. Common in older adults and people who avoid animal products without supplementing. Found in meat, fish, eggs, and dairy.
• Zinc. Involved in neurotransmitter regulation. Lower serum zinc has been observed in people with depression compared to controls.
• Iron. Low iron, particularly iron deficiency anaemia, is associated with fatigue, cognitive impairment, and depression, particularly in women of reproductive age.

The clinical evidence. What randomised trials show

The move from observational evidence to experimental evidence (randomised controlled trials, or RCTs) is the critical step in establishing causation rather than just association.

Subsequent trials and the growing evidence base

The SMILES trial was followed by several other RCTs testing Mediterranean or whole food dietary interventions for depression and anxiety:

• HELFIMED (Australia, 2019). Mediterranean-style diet supplemented with fish oil improved mental health in people with depression.
• AMMEND (2022). Mediterranean diet improved symptoms of depression in young men with moderate-to-severe depression.
• A 2025 systematic review of 21 RCTs found that the Mediterranean diet reduced depressive symptoms by 32 to 45% across included trials.

A 2022 meta-analysis of RCTs of dietary interventions for depression found significant improvements in depressive symptoms from dietary interventions, though the quality and consistency of trials varies.

The limits of the clinical evidence

Most dietary RCTs for mental health have been small, short, and conducted in Australia. Larger, longer trials in diverse populations (including UK populations) are underway but not yet reported. The effect sizes are meaningful but not as large as those seen with antidepressant medication in severe depression. The evidence is strongest for depression; the RCT evidence for anxiety and other mental health conditions is less developed.

The current position of researchers in the field, including the ISNPR: diet quality should be considered a complementary strategy in mental health care, alongside medication, psychotherapy, exercise, sleep, and social connection. Not a primary treatment in isolation.

The UPF connection. What high processing does to mental health

The 2024 BMJ umbrella review's finding that higher UPF consumption is associated with a 48 to 53% higher risk of anxiety and common mental disorders (convincing evidence) and 22% higher risk of depression (highly suggestive evidence) is striking. Several mechanisms are proposed:

1. Nutritional displacement. UPF-dominated diets are systematically low in the nutrients most important for brain function: omega-3 fatty acids, magnesium, zinc, folate, B vitamins, and polyphenols. When UPF displaces whole foods, the brain is chronically undersupplied with its building blocks.
2. Gut microbiome disruption. Emulsifiers and artificial sweeteners in UPF alter gut bacteria in ways associated with inflammation, increased gut permeability, and altered serotonin production. The gut-brain axis becomes a route through which a disrupted microbiome influences mood and cognition.
3. Pro-inflammatory profile. Diets high in UPF tend to raise systemic inflammatory markers. Neuroinflammation is a significant mechanism in depression.
4. Blood glucose volatility. UPFs are typically high in rapidly absorbed sugars and refined carbohydrates, producing the spikes and crashes associated with mood instability, fatigue, and anxiety.
5. Addictive-like eating patterns. The hyperpalatability of UPF (engineered combinations of sugar, fat, and salt) may drive overconsumption and dysregulate the dopamine reward pathways that are also implicated in depression and mood disorders.

Key foods for brain health

Based on the evidence above, certain foods and food patterns are most consistently associated with better mental health outcomes.

For browsing individual foods, see the fish and seafood, vegetables, grains, pulses, nuts and seeds, dairy, and eggs encyclopedia categories.

Diet patterns, not single foods

One of the most consistent findings in nutritional psychiatry research is that dietary patterns matter more than individual foods or nutrients. No single food or supplement reliably produces the brain health benefits seen with a high-quality overall dietary pattern.

The Mediterranean diet (characterised by high consumption of vegetables, fruit, whole grains, legumes, nuts, olive oil, and fish; moderate consumption of dairy; and low consumption of processed meat and refined foods) is the dietary pattern with the strongest and most consistent evidence for mental health benefit across observational studies and the most RCT evidence.

This is not coincidence. The Mediterranean diet happens to be:

• High in anti-inflammatory compounds (polyphenols, omega-3s)
• Rich in brain-relevant micronutrients (B vitamins, magnesium, zinc, folate)
• Supportive of gut microbiome diversity (fibre, fermented foods)
• Stabilising for blood glucose (fibre, whole grains, legumes)
• Low in UPF and refined sugar

It is also the dietary pattern associated with the lowest all-cause mortality, lowest cardiovascular disease risk, and strongest longevity data, as described in the whole foods guide.

The practical implication is that improving diet for mental health does not require memorising a list of "brain foods" or following a rigid plan. It means shifting the overall dietary pattern towards more whole, minimally processed foods and away from ultra-processed products.

What about supplements?

This is an area where marketing often runs well ahead of evidence. A meta-review of meta-analyses of nutrient supplements for mental disorders (Firth et al., 2019) summarised the state of play.

The important caveat: supplements are not food. A supplement cannot replicate the full benefit of a high-quality dietary pattern, which delivers nutrients in the context of the whole food matrix, alongside fibre, polyphenols, and other bioactive compounds that interact. The evidence for dietary patterns improving mental health is stronger and more consistent than the evidence for individual supplement use.

Supplements have a place for correcting documented deficiencies, particularly vitamin D, B12 in vegans, and iron in women with deficiency, but they are not a substitute for dietary improvement.

Practical steps. What this means for everyday eating

You do not need to follow a named diet or overhaul everything at once. The most evidence-based dietary shifts for mental health track closely with the general whole food dietary advice elsewhere on this site.

1. Eat two portions of oily fish per week. The single food-level change with the strongest evidence base for mental health, in addition to cardiovascular benefit. Salmon, mackerel, sardines, trout, and herring. Fresh, frozen, or tinned in olive oil or water.
2. Eat a wide variety of vegetables and fruit daily. Target at least five 80g portions. Aim for colour variety. Different colours carry different polyphenols, which feed different gut bacteria and have different anti-inflammatory profiles.
3. Choose whole grains over refined. Wholemeal bread, brown rice, oats, and wholegrains in place of white bread, white rice, and sugary cereals. This stabilises blood glucose and provides B vitamins and magnesium.
4. Include legumes regularly. Lentils, chickpeas, kidney beans. Rich in folate, magnesium, zinc, tryptophan, and prebiotic fibre. Aim for 3 to 5 servings per week at minimum. See the fibre guide for the broader picture.
5. Add a small handful of nuts and seeds daily. Walnuts for ALA; pumpkin seeds for zinc and magnesium; Brazil nuts for selenium. Small additions with meaningful micronutrient payoffs.
6. Reduce ultra-processed food. The 2024 BMJ evidence for UPF and mental health is among the strongest in the review. Reducing the proportion of UPF in the diet, and replacing it with whole food alternatives, addresses multiple mechanisms simultaneously.
7. Avoid blood glucose volatility. Limit high-sugar snacks, sugary drinks, and refined carbohydrate-heavy meals. Pair carbohydrates with protein, fat, or fibre to slow absorption.
8. Supplement vitamin D through winter. The NHS recommends 10 micrograms per day from October to March for everyone in the UK. Given the established link between vitamin D deficiency and depression, this is one of the most broadly applicable supplement recommendations.
9. Support your gut microbiome. Add fermented foods with live cultures (plain yogurt, kefir, sauerkraut, kimchi) and eat diverse plant fibres. The gut-brain axis is a meaningful pathway. See the gut health guide for the detail.

Key facts at a glance