A Real Dietary Treatment for Depression

A recent study demonstrates how a healthier diet can improve symptoms.

Posted Sep 26, 2018

I’m often asked in my work with patients about various diets and supplements that get promoted in books and blogs as miracle cures for everything from anxiety to autism.  As someone who tries to be very careful about medications, I want to be encouraging about nonpharmacological treatments, but at the same time, it’s important to base medical advice on real science, rather than hype. After all, pharmaceutical companies aren’t the only ones prone to making grandiose and exaggerated claims about their products. Supplement makers and fad diet promoters do the same thing, but for some reason, there is less public outrage and skepticism about these “natural” interventions.

What often happens is that particular diets or supplements often sound scientific and even make physiological sense as to why they theoretically might be useful for certain mental health problems, but nobody seems to have the time (or maybe the guts) to put rubber to the road and actually rigorously test the product in a real human clinical trial. 

This is why I was excited to read about an actual randomized trial in Australia from respected dietary researcher Felice Jacka and colleagues of a specific diet designed to help adults with major depressive disorder. The official name of the study was SMILES, which stands for Supporting the Modification of Lifestyle in Lowered Emotional States. (All clinical trials that want to be important and groundbreaking now need to come up with these rather forced acronyms.)

Perhaps not unexpectedly, the dietary treatment was not some flashy new supplement or bizarre new approach, but rather a general healthy Mediterranean-inspired diet that urged people to increase consumption of fruits, vegetables, lean protein, and whole grains while decreasing consumption of carbohydrates, sweets, and heavily processed foods. Importantly, participants were also allowed to continue the depression treatments that they were already doing, which was mainly psychotherapy, antidepressant medications, or some combination.  In this way, the study really was testing the added benefit of dietary modification rather than looking at what happens when diet is used as the primary intervention.

The 67 subjects in this study suffered from major depression that was rated as being in the moderate to severe range.  They also had baseline diets that were not particularly healthy in the first place.  Half of the sample was randomized to social support (basically friendly chats with a research assistant), while the other half received seven sessions of personalized nutritional counseling and motivational support to a “ModiMedDiet” that emphasized more healthy food choices as described above.  The counselors also focused on curbing alcohol use beyond two glasses of wine per day.

The results were very encouraging. Subjects in the dietary modification group generally did improve their eating habits and this, in turn, appeared to reduce their depressive symptoms. On their main instrument that tracked depression severity, subjects in the dietary modification group improved significantly more than those in the control condition.  In terms of raw scores, the mean depression score for the dietary modification group dropped from 26 to 15 over 12 weeks, while for the control group it fell from 25 to about 20.  This would be considered to be a fairly large effect that is comparable to—and even surpasses—some studies of antidepressant “augmentation” with other medications, such as antipsychotic agents, which carry with them the potential of some serious side effects.  By the end of the study, about a third of the subjects in the dietary group were rated as being “in remission” from their depression compared to only 8% in the control group. Anxiety scores also improved with the dietary intervention.  Improvement in depression was found to be independent of changes in weight.

The authors acknowledge that they can’t be sure exactly how a better diet improves depression, but they do note other research that suggests pathways related to decreased inflammation, antioxidant effects, and changes in one's gut bacteria can affect the brain. One aspect of the study that does muddy the waters a bit is their focus not only on diet but alcohol use as well, which can worsen depression.  I’d honestly be a little more confident in their conclusions had they demonstrated that the improvement occurred independently on any changes in alcohol consumption.

Also worth noting is that the subjects were obviously aware of what group they were in rather than being “blinded” as in the case of an active drug versus placebo trial.  Finally, the authors acknowledge that their sample size was relatively small and, indeed, smaller than they had hoped, perhaps reflecting how challenging it can be to get people to want to make substantive changes in how they eat.  Nevertheless, this is an important advance as the first (and long overdue) real randomized clinical trial that demonstrates how changing one’s diet and positively improve mental health.


Jacka FN, O'Neil A, et al. A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial). BMC Medicine 2017;15:23