Eating Better Cut Depression Symptoms by More Than Any Antidepressant Trial Expects

Most people who get a depression diagnosis leave the clinic with a prescription or a referral for therapy. A clinical dietician is rarely part of the conversation. The SMILES trial, published in BMC Medicine, is one of the first randomized controlled trials to test whether improving what people eat can meaningfully reduce the symptoms of a major depressive episode. The answer, at least in this early study, is a striking yes.

The ModiMedDiet Cut Depression Scores Far Beyond What Controls Achieved

Researchers enrolled 67 adults who had both a diagnosed major depressive episode and a poor-quality diet, defined by a Dietary Screener Tool score at or below 75. Participants were randomly assigned to one of two groups for 12 weeks. The dietary support group received seven one-hour sessions with a clinical dietician, who guided them toward what the researchers called the ModiMedDiet: a modified Mediterranean pattern built around whole grains, vegetables, fruits, legumes, low-fat dairy, nuts, fish, lean red meats, chicken, eggs, and olive oil, while cutting back on sweets, refined cereals, fried food, fast food, processed meats, and sugary drinks. The control group received the same number of sessions, but these were structured social support conversations about neutral topics, a protocol known as "befriending."

At 12 weeks, the dietary support group showed a 7.1-point greater improvement on the Montgomery-Asberg Depression Rating Scale (MADRS) compared to controls, a clinically meaningful gap with an effect size of Cohen's d = 1.16. Crucially, 32.3% of people in the dietary group achieved remission (a MADRS score below 10), compared to just 8% in the social support group. The number needed to treat for one additional remission was 4.1, a figure that compares favorably with many pharmacological interventions.

Depression in a Quarter of a Billion People Makes Diet a Scalable Target

Depression affects hundreds of millions of people globally, and existing treatments leave a substantial proportion of patients without adequate relief. Even for those who respond to antidepressants or therapy, access, cost, and side effects remain real barriers. If dietary improvement proves to be a genuine adjunctive treatment, it carries an unusual advantage: it is broadly accessible and, as the SMILES trial found, potentially cheaper than what patients are already eating. The research team estimated the ModiMedDiet cost approximately AU$112 per week in groceries, compared to participants' estimated baseline spend of AU$138 per week.

That cost finding matters because dietary interventions are often dismissed as impractical for people experiencing depression, who frequently struggle with motivation, appetite, and daily functioning. The 94% completion rate in the dietary support group suggests the intervention was well-tolerated even in a population with moderate-to-severe symptoms. A systematic review of 25 clinical nutritional trials found that Mediterranean-style diets reduce depressive symptoms by 32 to 45%, reinforcing that the SMILES result is not an isolated outlier. Research tracking younger populations points in the same direction: a longitudinal study of Canadian adolescents found higher consumption of sugar-sweetened beverages was associated with increased depressive and anxiety symptoms, while fruit and vegetable intake tracked with better psychological well-being.

How a Dietician-Led Protocol Moved Mental Health Scores

The intervention was not simply a pamphlet about eating vegetables. Each session combined nutritional education with motivational interviewing and goal-setting, and participants were given food hampers, recipes, and meal plans to reduce practical barriers. This combination of behavioral support and concrete resources likely mattered. Participants in the dietary group significantly increased their intake of whole grains, fruit, dairy, olive oil, pulses, and fish, and meaningfully reduced "extras" (the processed, high-sugar foods the diet aimed to minimize). Importantly, changes in dietary quality correlated directly with changes in MADRS scores within the intervention group: the more a person's diet improved, the greater their improvement in depression symptoms.

The improvements held up after controlling for weight change, BMI, self-efficacy, smoking, and physical activity, suggesting diet quality itself was driving the effect rather than indirect lifestyle shifts. The researchers point to several plausible biological pathways: reduced systemic inflammation, lower oxidative stress, improved gut microbiota composition, and enhanced brain plasticity. Behavioral changes tied to cooking, shopping, and establishing meal routines may also have contributed independent therapeutic benefit.

Small Sample and Unblinded Participants Limit the Conclusions

The SMILES trial is compelling, but it is a 67-person, 12-week study, and those constraints matter. With a sample this small, there is a meaningful chance the effect size is inflated relative to what a larger trial would find. Participants could not be blinded to their group assignment, introducing the possibility that those receiving dietary support had higher expectations of improvement and reported accordingly. Dropout rates also differed between groups: 94% completion in dietary support versus 73.5% in social support, an asymmetry that could bias the results.

The trial also recruited specifically from people with poor dietary quality at baseline, so the findings may not generalize to the broader population of people with depression who already eat reasonably well. As a broader review of the mechanisms connecting food and mental well-being notes, the field still needs to resolve questions around reverse causality (does depression cause poor eating, or poor eating worsen depression?) and optimal timing for nutritional interventions. The SMILES results are a signal worth pursuing, not a settled answer.

Dieticians as Part of Multidisciplinary Mental Health Teams

The trial's authors make a practical argument: clinical dieticians should be integrated into multidisciplinary mental health teams. Australian clinical guidelines already recommend addressing health behaviors including diet as part of mood disorder management, but dieticians rarely appear alongside psychiatrists and psychologists in practice. The SMILES results give that recommendation more empirical weight.

The next steps require replication in larger, more diverse samples with longer follow-up periods. Researchers also need to determine whether specific dietary components (omega-3s from fish, fermented foods supporting the gut microbiome, polyphenols from fruits and vegetables) account for most of the benefit, or whether the overall dietary pattern is what moves the needle. For now, the SMILES trial offers a well-designed if early piece of evidence that what ends up on someone's plate may be as relevant to their mental health care as what ends up in their medicine cabinet.

Evidence rating

EMERGING — 69/100

Caveats:

• Small sample size (n=67) means the effect size may be inflated and results should be interpreted cautiously.
• Participants were not blinded to their group allocation, introducing potential expectation bias.
• Dropout rates differed between groups (6% in dietary support vs. 26.5% in social support), which may have influenced the results.
• The study cannot establish which specific component of the dietary intervention drove improvement — dietary change itself, structured social contact with a dietician, or behavioral factors like cooking and meal planning.
• Gut microbiota pathway is proposed as one possible mechanism but was not directly measured in this trial.
• Funding was not disclosed in the available materials; independent replication is needed before clinical adoption.

Twelve-week single-blind RCT (n=67) comparing a Mediterranean-style dietary intervention with a social support control in adults with moderate-to-severe depression. The dietary group showed significantly greater improvement on the MADRS (Cohen's d = –1.16) and higher remission rates (32% vs. 8%), though the small sample size and differential dropout rates limit confidence in the magnitude of the effect. No independent replication of this specific trial exists, though observational literature on diet and depression risk is broadly consistent with the direction of findings.

References

1. Felice N. Jacka, Adrienne O’Neil, Rachelle Opie, et al. (2017). A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial). BMC Medicine. https://doi.org/10.1186/s12916-017-0791-y
2. Maria Dimopoulou, Aliki Dimopoulou, Olga Gortzi (2025). Dietary Patterns and Mental Health Across the Lifespan: A Systematic Review of Randomized Clinical Trials. Psychology International. https://doi.org/10.3390/psycholint7040087
3. Julia Dabravolskaj, Karen A. Patte, Shelby Yamamoto, Scott T. Leatherdale, Paul J. Veugelers, Katerina Maximova (2024). Association Between Diet and Mental Health Outcomes in a Sample of 13,887 Adolescents in Canada. Preventing Chronic Disease. https://doi.org/10.5888/pcd21.240187
4. (2020). Food and mood: how do diet and nutrition affect mental wellbeing?. BMJ. https://doi.org/10.1136/bmj.m4269