Beans, Greens, and the Best Foods for the Brain

Fermented Foods, the Microbiome, and Conclusions

Like gluten, discussion of the microbiome now appears almost daily in lay and professional media. "A gastro friend of mine thinks we should play a drinking game," joked Dr Deans, "where anytime someone mentions the microbiome, we take a drink."

Our microbiomes contain well over 1 million genes, compared with our 23,000 genes. Furthermore, the commensal microbiome accounts for 90% of the cells in our bodies. Among other functions, these gastrointestinal symbiotes help form and maintain our immune system and aid in digestion, so their health is critical to our health. The understanding of how microbiota contribute to our mental and medical well-being is rapidly advancing.

For example, there is considerable overlap between irritable bowel syndrome and depression and anxiety. "My contention is that they are the same pathology that are expressed in different phenotypes," posited Dr Deans. Gut pathogens cause inflammation and increase factors like IL-6 and interferon gamma—findings also seen in depression—ultimately reducing the conversion of tryptophan to serotonin. Dr Deans wonders whether chronic inflammation might be at the core of conditions such as depression and anxiety and introduced the concept of psychobiotics, or the idea that microbiota can influence the mind and mental health.

One of the most powerful interventions to alter our microbiome is diet. Research shows that stressed mice experienced changes in the gastrointestinal microbiota, reflecting the gut-brain relationship.^[12] There are 260 million neurons connecting the gut and the brain; furthermore, many commensal gut bacteria make neurotransmitters and communicate with the brain via the vagus nerve. "I don't know what they're saying to us," joked Dr Deans, "but let's just say that if you get a fecal transplant, you want to get if from a happy, mellow person."

Although the science of probiotic therapies is relatively young, it's clear that these commensal organisms co-evolved with us and are adapted to our diet. One study out of The Netherlands found that a 4-week regimen of multispecies probiotics can reverse cognitive reactivity to sad mood.^[13] Another study^[14] explored what would happen if a group of African Americans in Atlanta swapped diets with a group of rural black South Africans. The investigators were curious to see whether dietary differences could help explain the drastically differing rates of colon cancer between the two populations (65:100,000 in African Americans vs < 5:100,000 in rural South Africans). The South African diet was high in fiber and prebiotics, while the American diet was much higher in junk food, refined carbohydrates, and animal fats. Within 14 days of switching to the South African diet, healthy butyrate-producing microbial species increased by 258% in the American population. Butyrate is a byproduct of bacterial fermentation in the colon and is thought to protect against colon cancer.

Dr Deans then mentioned the recent media coverage of a geneticist who put his son on a 10-day all-McDonald's diet and measured his microbiome before and after. It was found that the son reduced the diversity of his microbial species by 40%, as assessed by three different labs. (In all fairness, he was restricted to burgers and fries and not the healthier options that McDonald's offers.)

Finally, to close out the session, Dr Ramsey returned to the stage and asked, "So, can you eat to build a better brain? We think that you can if you focus on dietary patterns and not a single food here or there." He also reminded the audience to help their patients identify and increase their consumption of nutrient-dense foods and to "eat the rainbow," assuming, he cautions, that the rainbow doesn't include bright red Gummi Bears.

"I don't know of anything else that can potentially decrease the risk of depression in a population by 40%,^[3]" he concluded. "Perhaps diet is the closest we've come to prevention in psychiatry."

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