Increasing Research on Microbiome, Gut-Brain Connection Points to Promise of Nutritional Interventions

By Richard Karel

In the last decade, scientists have deepened their understanding of how a healthy gut microbiome impacts systemic inflammation and mental health. While most research on specific nutritional interventions is equivocal, there is promising evidence regarding the role of the Mediterranean diet and targeted use of vitamin D and omega-3s in alleviating depression and childhood attention-deficit/hyperactivity disorder (ADHD).

This information was discussed at the session “Nutritional Interventions in Psychiatry: What Is the Evidence?” at APA’s online 2021 Annual Meeting. The major takeaways: a commonsense approach to dietary interventions, focusing on healthier eating patterns with the Mediterranean diet as a general model; the advisability of assessing new patients for micronutrient deficiencies, particularly vitamin D and vitamin B12; and considering the intake of omega-3 fatty acids.

While the evidence supporting specific nutritional interventions is not overwhelming, there is virtually no risk in using nutritional and nutrient interventions, panelists observed.

Umadevi Naidoo, M.D., is the director of Nutritional and Metabolic Psychiatry at Massachusetts General Hospital and a chef and culinary instructor. She said that Nobel laureate Joshua Lederberg coined the term “microbiome” to refer to the community of “commensal, symbiotic, and pathogenic microorganisms that literally share our body space.”

The gut microbiome—with 100 trillion microbes—is in effect another organ in the body. The gut is connected to the brain via the vagus nerve, quite literally linking food and feelings, said Naidoo. “We are just starting to gain insight into how nutrition impacts mental health, but this is an exciting scientific frontier.”

There is evidence that dysbiosis—disruption of the microbiome—promotes systemic inflammation and that this, in turn, can lead to neuroinflammation and a dysfunctional hypothalamic pituitary axis, associated with greater perceived stress and increased pain perception.

The findings around which foods encourage a healthy microbiome are not surprising, said Naidoo. A diet high in fiber, fruits, vegetables, fermented foods, whole grains, nuts, seeds, and legumes enhances the microbiome—a good model being the Mediterranean diet, while highly processed foods, transfats, artificial sweeteners, and excessive consumption of caffeine and alcohol undermine the microbiome.

Many small trials of varying quality have explored the interplay between diet and depression. An Australian trial of 67 individuals (SMILES-Supporting Modification of lifestyle in Lowered Emotional States) found a meaningful reduction in symptoms of moderate to severe depression—33% in the dietary group versus 8% in the control group, according to panelist Glynis McGowan, M.D., of Brigham & Women’s Hospital. Other studies have buttressed this conclusion. The limitations of these studies include modest size and trial design, but to date the Mediterranean diet has the most evidence for a positive role in supporting mood, said McGowan.

A key area of concern is the propensity of antipsychotic medications to induce weight gain, which increases the probability of developing metabolic syndrome. Ann Felhofer, M.D., of Brigham & Women’s Hospital, cited studies that looked at nonpharmacological interventions in patients dealing with antipsychotic drug-induced weight gain. While there were positive results, the studies were limited by the inability to isolate nutritional interventions from other lifestyle changes.

The targeted use of micronutrients, particularly vitamin D and omega-3 fatty acids, has shown encouraging results in alleviating major depression and symptoms of childhood ADHD, according to session chair Jessica Principe, M.D. Principe and colleagues at Brigham & Women’s Hospital conducted a meta-analysis of a number of randomized clinical trials and cited a meta-analysis on vitamin D and childhood ADHD. ■