Can diet changes treat depression?
Not on its own. In a 12-week randomized controlled trial, a dietary improvement program added on top of existing treatment improved depression symptoms significantly more than a matched social support program, and remission was reached by 32.3% of the dietary group versus 8.0% of the control group. The trial enrolled 67 adults with moderate to severe depression, and 55 of them were already receiving psychotherapy, medication, or both, so the diet program was tested as an addition to care, not as a replacement for it.
The dietary arm received seven individual nutritional consulting sessions delivered by a clinical dietician. The control arm received a social support protocol matched to the same visit schedule and session length, which is what makes the comparison informative: both groups got the same amount of professional attention.
What the data show:
- Effect on symptoms: The dietary support group improved significantly more than the social support control between baseline and 12 weeks on the MADRS, t(60.7) = 4.38, p < 0.001, Cohen’s d = -1.16, a large effect
- Remission rates: 32.3% (10 of 31) with dietary support versus 8.0% (2 of 25) with social support, where remission was defined as a MADRS score below 10
- Study scope: 166 individuals assessed for eligibility, 67 enrolled (33 dietary support, 34 control), over 12 weeks
- Design: A single blind, parallel-group randomized trial of an adjunctive dietary intervention, with 55 of the 67 participants using some form of therapy: 21 psychotherapy and pharmacotherapy combined, 9 psychotherapy only, 25 pharmacotherapy only
The SMILES trial, published in BMC Medicine in 2017, tested whether improving diet has a therapeutic effect on an existing major depressive episode, a therapeutic impact the investigators described as largely unknown.
Dr. Kumar’s Take
The finding I keep coming back to is that the comparison group was not a waitlist. Both arms saw a professional on the same schedule for the same length of time, and the dietary arm still separated clearly on the MADRS with a large effect size. That is a harder test than most lifestyle trials set for themselves.
I want to be precise about what this trial does and does not show, because it gets overstated constantly. The dietary program was adjunctive. Most participants stayed on their psychotherapy, their medication, or both, and the diet sessions were layered on top. So this is evidence that dietary counselling adds something to depression treatment, not evidence that food replaces treatment. If you are on an antidepressant or in therapy, the reading of this trial is to keep going and add nutritional support, not to swap one for the other.
The remission numbers are the part I find clinically meaningful. Roughly a third of the dietary group dropped below a MADRS score of 10 in 12 weeks, against 8.0% in the social support arm. Remission, not just a few points of symptom improvement, is what patients actually care about. This is a small trial with 67 enrolled and it needs replication at scale, but it is a reasonable basis for taking diet seriously as part of a depression treatment plan rather than as an afterthought.
Study Snapshot
SMILES was a 12-week, parallel-group, single blind randomized controlled trial of an adjunctive dietary intervention in the treatment of moderate to severe depression. Participants were randomized to either dietary support, consisting of seven individual nutritional consulting sessions with a clinical dietician, or a social support control condition delivered on the same visit schedule and for the same session length. The primary endpoint was depression symptomatology, measured with the Montgomery-Åsberg Depression Rating Scale (MADRS) at 12 weeks. Secondary outcomes included remission, change in symptoms, mood, and anxiety. Analyses used a likelihood-based mixed-effects model repeated measures approach, with sensitivity analyses to test how robust the estimates were.
Results in Real Numbers
Investigators assessed 166 individuals for eligibility and enrolled 67: 33 to the dietary intervention and 34 to the control condition. Of those enrolled, 55 were already using some form of therapy, specifically 21 using psychotherapy and pharmacotherapy combined, 9 using psychotherapy alone, and 25 using pharmacotherapy alone. At 12 weeks, complete data were available for 31 participants in the dietary support group and 25 in the social support control group.
On the primary endpoint, the dietary support group showed significantly greater improvement on the MADRS between baseline and 12 weeks than the social support control group, t(60.7) = 4.38, p < 0.001, with Cohen’s d of -1.16, a large effect size.
Remission, defined as a MADRS score below 10, was achieved by 32.3% of the dietary support group (10 of 31) and 8.0% of the social support control group (2 of 25).
Who Benefits Most
Adults with moderate to severe depression who are already in treatment and willing to work through a structured program with a dietician are the group this trial actually studied. That is the population the results apply to most directly.
People looking for a complementary addition to existing depression care are the right audience here. The trial was designed as an add-on, and 55 of the 67 enrolled participants were using psychotherapy, pharmacotherapy, or both.
Safety, Limits, and Caveats
This was a small trial. Sixty-seven people were enrolled and 56 had complete data at 12 weeks, which is enough to detect a large effect but not enough to settle the question. It was also single blind, which is unavoidable when the intervention is food, and it ran for 12 weeks, so it says nothing about whether the benefit holds at a year.
The intervention required seven individual sessions with a clinical dietician. That is a real commitment of time and effort, and it may be harder to sustain for someone in the middle of a depressive episode. It also means the trial tested supported dietary change, not simply being told to eat better.
The dietary intervention was adjunctive, so the results support diet as an addition to established treatment. They do not support stopping an antidepressant or leaving therapy.
Practical Takeaways
- Treat structured dietary support as an add-on to your existing depression treatment, not as a substitute for therapy or medication
- Work with a clinical dietician if you can, since the trial’s benefit came from repeated individual sessions rather than general advice
- Expect the commitment to be real: this was seven individual consulting sessions over 12 weeks
- Judge the result on remission, which was 32.3% with dietary support versus 8.0% with social support alone
- Keep in mind that the evidence base here is one small randomized trial and needs replication before it carries the weight of a first-line treatment
What This Means for Depression Treatment
SMILES was designed to test whether changing diet has a therapeutic effect on an existing major depressive episode. Using a randomized design with an attention-matched control, it found a large improvement in depression symptoms and a higher remission rate in the dietary support arm.
That argues for building nutritional counselling into comprehensive mental health care alongside existing treatments, and for running larger and longer trials to test how durable the effect is.
Related Studies and Research
Diet Interventions for Depression: Review and Recommendations
Episode 31: Depression Explained, The Biology Behind the Darkness
Episode 32: Depression Recovery Roadmap: A Step-by-Step, Evidence-Based Plan
FAQs
Can diet alone treat depression?
This trial does not answer that. The dietary program was adjunctive, and 55 of the 67 enrolled participants were using psychotherapy, pharmacotherapy, or both alongside it. What it shows is that dietary support added to existing treatment improved symptoms more than matched social support.
How was the dietary intervention delivered?
Through seven individual nutritional consulting sessions with a clinical dietician over 12 weeks. The control group received a social support protocol on the same visit schedule and for the same session length.
How quickly did participants see benefits?
The trial ran for 12 weeks, and the primary endpoint was measured at 12 weeks, where the dietary support group had improved significantly more on the MADRS than the control group.
Bottom Line
In a 12-week randomized controlled trial of 67 adults with moderate to severe depression, adding structured dietary support to existing treatment improved depression symptoms significantly more than matched social support, with a large effect size and remission in 32.3% of the dietary group versus 8.0% of controls. It is a small trial and the diet program was an addition to therapy and medication, not a replacement for them.
