This Diet Helps Many With Depression

AS AN ONCOLOGIST, I often witness firsthand the emotional toll cancer takes on my patients, not just physically but psychologically. 

For many, the depression shadows the journey.

“There is no greater sorrow than to recall happiness in times of misery.” — Dante Alighieri.

And while therapy and medication remain essential tools, they don’t always work for everyone. That’s why I’ve become increasingly curious about something more primal: the food on our plates.

Can diet succeed where other approaches falter? The answer, emerging from high-quality studies, is a cautious but compelling “yes.”

The SMILES Trial: A Nutritional Psychiatry Landmark

The strongest evidence comes from the SMILES trial, published in 2017 in BMC Medicine. 

This randomized controlled study asked: 

What happens if people with moderate to severe depression improve their diet?

Instead of focusing solely on therapy or medication, researchers explored whether a shift toward a nutrient-rich, Mediterranean-style diet could ease depressive symptoms.

Study Details

The SMILES trial was a 12-week study that tested whether improving diet could help treat moderate to severe depression.

Researchers assigned study participants to either:

• A modified Mediterranean diet (rich in vegetables, legumes, whole grains, fish, olive oil, and modest red meat). Group members received personalized nutrition support — seven one-on-one sessions with a clinical dietitian.
• Social support group. This group met with someone on the same schedule for friendly conversation and emotional support without any dietary advice.

Study Methods and Goals

The main goal was to see how much depressive symptoms improved after 12 weeks using a standard clinical scale called the MADRS. 

Researchers also looked at how many people went into remission and whether symptoms like anxiety and low mood changed over time. 

They used a rigorous statistical method to ensure the results were reliable and even tested the findings using several different models to check their validity.

Results

After 12 weeks, the dietary group experienced significantly greater improvement in depressive symptoms. 

Nearly one in three (32%) individuals achieved full remission — nearly three times more than the control group.

This study is the first intervention study to show that diet improvement can help treat depression.

How Diet May Affect Mood

Emerging science suggests several mechanisms by which food may influence mental health:

• Inflammation. Diets high in sugar, refined carbs, and processed foods can fuel chronic inflammation, which has been linked to depressive symptoms. Anti-inflammatory diets like the “Mediterranean diet” may help reduce this burden. 
• Gut-Brain Axis. Your gut microbiome produces neurotransmitters like serotonin and GABA. A healthy, fiber-rich diet can foster microbial diversity and improve mood.
• Nutrient Deficiency. Low omega-3 fatty acids, B vitamins (especially folate and B12), magnesium, and zinc are associated with depression. Whole, unprocessed foods help restore these crucial nutrients.

As writer and essayist Veronique Greenwood recently wrote in Harvard Magazine: 

“You are what your microbes consume.”

What Should a Depression-Fighting Diet Look Like?

The common thread in the highest-quality research is a dietary pattern, not individual superfoods. 

Here’s what the evidence supports:

 ✅ Plenty of fruits and vegetables (especially leafy greens and berries)
 ✅ Whole grains instead of refined carbohydrates
 ✅ Legumes, nuts, and seeds for fiber and minerals
 ✅ Fatty fish like salmon or sardines, for omega-3s
 ✅ Olive oil as a primary fat source
 ✅ Limit ultra-processed foods, sugary snacks, fried items, and soft drinks

For me, it’s not about perfection — it’s about consistency.

Supplements

In My Practice

I’ve started asking about diet more often. 

Not to replace therapy or medications but to augment them. 

When my patients with cancer tell me they feel chronically down, even after their scans come back clean, I gently ask, “What’s your diet been like lately?” 

The conversation often reveals patterns that might be adding fuel to the fire.

My Take – This Diet Helps Many With Depression

As compelling as the SMILES trial is — especially as someone interested in non-pharmacologic strategies for depression — there are a few limitations and concerns worth pointing out:

• Small sample size. This study has a relatively small sample size, with only 67 participants randomized and 56 completing the 12-week assessment. This sample size raises the possibility of overestimating effect sizes and limits generalizability.
• Single-blind design. Only the outcome assessors were blinded. Participants knew which group they were in — dietary counseling or social support — which could have introduced expectancy bias. If someone told me my diet might treat my depression, I might be more hopeful (and possibly report better outcomes) even if the physiological effects were modest.
• Motivated sample. These were people willing to enroll in a dietary intervention trial for depression, likely more health-conscious and motivated than the average person with major depression. That could skew results toward success, especially in a study reliant on behavior change.
• Limitations of the control group. The control group received “befriending” or social support, which is meaningful but arguably less structured or empowering than personalized nutrition counseling. It may not have matched the intervention in perceived value or engagement.
• Dietary adherence. While the study reports an improvement in diet quality, it’s unclear how strictly participants followed the dietary advice or how much adherence correlated with symptom improvement. More granular data here would be helpful.
• The follow-up period was short — the study only lasted 12 weeks. We don’t know whether the antidepressant effects persisted after the intervention ended or whether a relapse occurred. Long-term efficacy and sustainability remain open questions.
• Confounding from concurrent therapy. Many participants were already receiving psychotherapy or pharmacotherapy. While real-world relevant, this makes it harder to isolate the true independent effect of dietary change.
• Generalizability to severe or treatment-resistant depression is uncertain. Although the study included people with moderate to severe depression, it’s unclear how this would apply to those with chronic, recurrent, or treatment-resistant forms of the illness.

That said, the effect size was large, and the number needed to treat to see an effect was strikingly low (4.1) — not something we often see in psychiatric interventions. 

So, while I have criticisms, I also think this was a well-executed trial that opened the door to more rigorous studies on food as medicine for the mind.

Final Thoughts: This Diet Helps Many With Depression — Why Aren’t We Talking About It?

“Let food be thy medicine,” offered Hippocrates. 

While poetic, we now know it’s more complex than that. 

But the idea that what we eat might lift the darkness, even slightly, is empowering and deeply human.

I’ll end with Mary Oliver, an indefatigable guide to the natural world:

“Tell me, what is it you plan to do with your one wild and precious life?”

Maybe one answer is this: eat in a way that nourishes both body and mind.

Nutritional psychiatry: the present state of the evidence | Proceedings of the Nutrition Society
www.cambridge.org

Food and mood: how do diet and nutrition affect mental well-being?
www.bmj.com

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