Can Diet Treat Depression?

I once worked with a man with unremitting bipolar II depression who had not responded to over a dozen medication trials. One day he strolled in with a bright affect and renewed interest in life. Perplexed, I asked him what had made the difference. “I gave up fast food a few months ago,” he said.

Recently, the first randomized controlled trial to test that hypothesis in unipolar depression was released. Using a modified version of the Mediterranean diet, Australian researchers randomized 67 patients with moderate to severe depression to 3 months of either dietary counseling or supportive therapy as an add-on to their usual care. The dietary approach outperformed supportive therapy, with an impressive effect size of 1.16.[1] To put that in perspective, it’s similar to the effect size of amphetamine salts in ADHD (1.0), and larger than that for modern antidepressants in major depression (0.3).[2,3]

Although supported by large epidemiologic and basic science studies,[1] the idea that diet can treat depression still feels like a sea change for psychiatry. The small sample size and lack of replication are reasons to be skeptical. The researchers also worked with an enriched sample, recruiting subjects whose diet was poor to begin with, so the results may not generalize to those who are already eating well.

The authors did take care to ensure that factors other than diet did not account for the improvement. Healthy diets can trigger a virtuous cycle of other mood-lifting changes, and they controlled for weight loss, perceived self-efficacy, physical activity, and nicotine use. Both groups received 7 hour-long sessions and placebo-enhancing rationales for their assigned interventions.

The actual intervention was a simplified version of the Mediterranean diet called the ModiMedDiet.[4] It does not restrict calories, but encourages more vegetables, fruits, nuts, beans, whole grains, fish, lean meats, and healthy oils; and less fried, fast, or processed foods and simple sugars. Moderate red meat consumption was encouraged, based on epidemiologic studies that link both excessive and restrictive intake of red meat to depression.

The fact that these depressed patients were able to make significant changes to their diet is remarkable in itself. Patients who are short on such motivation may be encouraged to know that small changes can also make a difference. Flavanol-rich foods, such as dark chocolate, green and black teas, and berries, improve mood and cognition through neuroprotective effects.[5-7] In a recent study of older adults, just a quarter cup of concentrated blueberry juice a day improved cognitive function after 3 months (randomized, controlled design; n=26).[8]

More examples of small dietary changes:

• Just 2 extra servings a day of fruits and vegetables can enhance motivation and vitality, according to a controlled trial in healthy young adults.[9]

• Even partial adherence to the Mediterranean diet lowers the risk of dementia (though full adherence brings greater benefit).[10]

• Daily intake of probiotics, whether through diet or supplements, reduces depression and anxiety.[11]

Another adaptation of the Mediterranean diet that is gaining popularity is the MIND Diet, which slows cognitive decline and prevents dementia.[10,12] U.S. News recently ranked this diet No. 3 in its list of top diets for health (No. 1 and No. 2 are the plans that the MIND Diet is based on: the DASH and the Mediterranean). The MIND and ModiMed diets are very similar, so I blended them together in a brief guide for patients.

Both of these brain diets allow 1 to 2 standard drinks of alcohol a day, with a preference for red wine. That recommendation might need adjustment in light of new research linking even moderate levels in the 1 to 2 daily drink range to hippocampal atrophy.[13] The creator of the MIND diet plans to remove alcohol in her next trial.

It’s not known whether the Mediterranean diet will have similar benefits in bipolar depression, but with its neuroprotective effects it’s a good bet that it will. Even if this diet doesn’t lift mood, there are good reasons to recommend it for bipolar disorder as well, given the high rates of cognitive and metabolic problems in that population.[14]

The future psychiatrist may need to know as much about food as pharmacology. For now, it’s enough to know that basic, sensible dietary changes can make a significant difference for both physical and mental health.

Dr. Aiken is the Director of the Mood Treatment Center and an Instructor in Clinical Psychiatry at the Wake Forest University School of Medicine. He does not accept honoraria from pharmaceutical companies but receives honoraria from W.W. Norton & Co. for Bipolar, Not So Much, which he coauthored with James Phelps, MD.