How What You Eat Affects How You Feel

We rarely think of food as something that affects our mood. A bad day calls for comfort food, not the other way around. But a growing body of research suggests that the relationship between diet and mental health runs deeper than we assumed — and in both directions.

The SMILES trial: a turning point

In 2017, Australian researchers published what became a landmark study in nutritional psychiatry. The SMILES trial was a randomized controlled trial that tested whether dietary improvement could reduce symptoms of major depression. Participants with moderate-to-severe depression received either nutritional counseling (focused on a Mediterranean-style diet) or social support as a control.

After 12 weeks, the dietary group showed significantly greater improvement in depression symptoms. In fact, 32% of participants in the diet group achieved remission, compared to just 8% in the control group (Jacka et al., 2017).

This was one of the first rigorous trials to demonstrate that changing what you eat can meaningfully improve clinical depression — not just general wellbeing.

It’s not just about depression

A comprehensive review published in the BMJ examined how diet and nutrition affect mental wellbeing more broadly. The authors found consistent evidence that poor nutrition contributes to low mood and that improving diet quality can protect both physical and mental health. They noted that dietary patterns high in fruits, vegetables, whole grains, and fish are associated with reduced risk of depression, while Western-style diets heavy in processed foods and sugar are linked to worse mental health outcomes (Firth et al., 2020).

Anxiety tells a similar story. A scoping review analyzing over 1,500 studies found associations between less anxiety and higher intake of fruits, vegetables, omega-3 fatty acids, and what researchers categorize as “healthy” dietary patterns. Conversely, diets high in sugar, refined carbohydrates, and processed foods were linked to higher anxiety levels (Aucoin et al., 2021).

The gut-brain connection

One of the most fascinating explanations for the diet-mood link involves your gut. The gut-brain axis — a bidirectional communication system between your digestive tract and your brain — is increasingly recognized as a key pathway through which food influences mental health.

A review in Advances in Nutrition outlined how diet shapes the gut microbiome, which in turn produces neurotransmitters, regulates inflammation, and communicates directly with the brain through the vagus nerve. The composition of your gut bacteria, shaped largely by what you eat, appears to play a role in mood regulation, stress response, and even cognitive function (Berding et al., 2021).

The practical implication: a diverse diet rich in fiber, fermented foods, and whole grains feeds the bacterial communities that support mental health. A monotonous diet of processed foods does the opposite.

The bigger picture

A review in European Neuropsychopharmacology summarized the emerging field of nutritional psychiatry, concluding that diet and nutrition have significant effects on mood and mental wellbeing. The authors emphasized that while the field is still developing, the association between poor diet and mood disorders — including both depression and anxiety — is consistent across populations and study designs (Adan et al., 2019).

Similarly, a narrative review in Nutrition Reviews highlighted that healthy eating patterns meeting food-based dietary recommendations may help both prevent and manage depression and anxiety. The authors called for nutrition to be integrated into mental health treatment strategies (Kris-Etherton et al., 2021).

What this means for you

None of this suggests that diet alone can cure mental illness. Depression and anxiety are complex conditions influenced by genetics, environment, relationships, and more. But the evidence increasingly supports that what you eat is one modifiable factor worth paying attention to.

Small, practical changes can make a real difference:

• Prioritize whole foods — fruits, vegetables, legumes, nuts, whole grains, fish.
• Reduce ultra-processed food — packaged snacks, sugary drinks, fast food.
• Don’t skip meals — blood sugar crashes affect mood and concentration.
• Eat diverse foods — variety supports a healthy gut microbiome.

If you’re looking to improve your eating habits, start with structure. Knowing what you’ll eat each day removes the guesswork and makes healthy choices the default — which is exactly what the research on meal planning shows, too.