Around the turn of the fourth century BCE, Hippocrates wrote, “Let food be thy medicine, and medicine be thy food,” and with this same frame of mind, pondered the nature of mental illness. He believed that depression was caused by an overabundance of black bile and that insanity (hysteria) was, at least in females, due to the position of a woman’s uterus. His concept of the ‘four humors’ left much to be desired but is valuable today in its emphasis of the interplay between lifestyle and health, and consequently on the holistic treatment of disease. Furthermore, in his conception of disease, Hippocrates recognized that the mind and the body were not separate entities, but equally beholden to the health of the whole organism. Therefore, to treat diseases of the mind it made sense to consider the multitude of physical factors that could influence a person’s overall health. In that vein, I decided to dig into the idea that dietary interventions might be used as a strategy to augment the treatment of major depressive disorder (MDD).
The idea that what you eat can affect your mood is appealing on an intuitive level. Just about everyone has experienced the sensation of feeling ‘gross’ after several days of consuming junk food or reached for comfort food to temporarily boost our mood. A wide variety of diets have been linked to an improved mood to varying degrees1. However, nutrition studies are notoriously hard to design and implement, so conclusions based on these studies usually require a lot of corresponding evidence across the literature to buttress these findings.
One of the best-studied dietary patterns is the Mediterranean diet, which emphasizes whole fruits and vegetables, whole grains, and olive oil as the primary fat source has been shown to have a positive effect on cardiovascular health, diabetes, and cognitive decline2. Likely as a result of these successes, the diet features prominently in studies examining the effect of diet on depression. A systematic review and meta-analysis conducted in 2018 examined 41 observational studies of diet and mood and found the most support for the Mediterranean diet decreasing feelings of depression3. Another diet that rose to the top was the anti-inflammatory diet, which minimizes processed foods and emphasizes whole grains, fruits, and vegetables.
Unfortunately, another systematic review and meta-analysis conducted in 2019 examining 14 observational studies showed no effect of the Mediterranean diet on mood. In fact, a subgroup analysis of several of these studies actually found the Mediterranean diet to have a deleterious effect4. Thus, the evidence for the effect of the Mediterranean diet on feelings of depression is mixed but likely shows a somewhat positive relationship with the heterogeneity of findings implying that the effect size is small if indeed present.
After addressing the question of whether diet effects mood, the next idea to be tested is whether or not an intervention to change diet is efficacious. For this, we turn to randomized controlled trials (RCTs). To this end, a 2014 systematic review of RCTs found that out of 17 studies examined, 8 (47%) exhibited an effect on mood while the other 9 demonstrated no significant effect5. Notably, interventions specifically utilizing the Mediterranean diet fell equally in each camp. Additionally, the majority of studies overall were non-dogmatic about their dietary approach and gave individualized advice to each participant.
Finally, given some demonstration of limited efficacy as an intervention, the next question is generalizability. I began this investigation with the hypothesis that physicians could use diet to augment treatment for major depressive disorder, and while the previously mentioned studies lend credence to that general idea, only one of the studies discussed actually involved a population with MDD. This study randomly distributed a leaflet to 80 patients in a psychiatric clinic either containing actionable recommendations for improving diet, sleep, exercise, and sun exposure, or a leaflet that recommended only ‘doing what felt right’ for each of the four lifestyle domains. At 6-month follow-up, those in the treatment group were significantly more likely to achieve remission of their depression, significantly more likely to experience a positive response to treatment (<50% decrease in symptoms) than those in the control6. This is an exciting finding but is tempered by the relatively small sample size and would need to be replicated before much stock was placed in it.
Overall, is there a role for dietary change in the treatment of depression? Maybe.
This seems almost infuriatingly vague but in science, even negative results are valuable and taken in the context of the limited literature linking diet with mood, I believe this is the strongest statement that can be made. The overall direction of the literature is positive and probably represents at least a weak relationship, and though studies of dietary interventions produced mixed results, there is some support for the idea that instituting a dietary change could help to improve mood in patients with MDD. Further, there is not consistent support for any one dietary pattern—though the Mediterranean diet probably warrants further study—and the aggregate of evidence seems to support the idea that other lifestyle recommendations made concurrently are also important in the treatment of depression.
In all, there is not sufficient evidence to recommend dietary interventions solely for the treatment of major depressive disorder. However, considering the holistic treatment of a person there is still significant value in encouraging dietary change to benefit a patient’s overall health. An intervention for this reason is certainly worthwhile, so, notwithstanding the questionable effects on depression, it is still incumbent upon healthcare providers to ask about diet and to help to set people on the path towards health. This involves not only knowing what is true, but also what is not. A scientific outlook involves not only openness to new ideas, but a skepticism to unverified information. The landscape of popular media on nutrition is replete with examples of overreaching and overpromising, and though adopting these new trends generally doesn’t cause patients harm (with a few very notable exceptions), it ultimately undermines trust in the scientific method, and if unverified claims are parroted by physicians, the profession as well. Thus, while I encourage my colleagues to evangelize about the many benefits of good nutrition, I also believe it is important to preach humility and continuous learning.
In the end, when a patient asks me if there is something they can eat to help with their depression, I will respond with an enthusiastic “maybe,” but then spend my time directing them towards evidence-based dietary patterns to improve cardiovascular health or diabetes with the hope that their mood might improve as a side benefit.
Learn more about nutrition in clinical medicine.
References:
- Opie, R., Itsiopoulos, C., Parletta, N., Sanchez-Villegas, A., Akbaraly, T., Ruusunen, A., & Jacka, F. (2016). Dietary recommendations for the prevention of depression.Nutritional Neuroscience, 20(3), 161-171. doi:10.1179/1476830515y.0000000043
- https://www.medicalnewstoday.com/articles/149090#benefits
- Lassale, C., Batty, G.D., Baghdadli, A., Jacka, F., Sanchez-Ville- gas, A., Kivimaki, M., Akbaraly, T., 2018. Healthy dietary indices and risk of depressive outcomes: a systematic review and meta– analysis of observational studies. Mol. Psychiatry.
- Shafiei, F., Salari-Moghaddam, A., Larijani, B., Esmaillzadeh, A., 2019. Adherence to the Mediterranean diet and risk of depres- sion: a systematic review and updated meta-analysis of obser- vational studies. Nutr. Rev. 77, 230–239.
- Opie, R. S., O’Neil, A., Itsiopoulos, C., & Jacka, F. N. (2015). The impact of whole-of-diet interventions on depression and anxiety: A systematic review of randomised controlled trials. Public Health Nutrition,18(11), 2074-2093. doi:10.1017/s1368980014002614
- Garcia-Toro, M. (2012). Hygienic-dietary recommendations in patients with depression. Http://isrctn.org/. doi:10.1186/isrctn59506583
- Adan, R. A., Van der Beek, E. M., Buitelaar, J. K., Cryan, J. F., Hebebrand, J., Higgs, S., . . . Dickson, S. L. (2019). Nutritional psychiatry: Towards improving mental health by what you eat. European Neuropsychopharmacology,29(12), 1321-1332. doi:10.1016/j.euroneuro.2019.10.011
