COMMENTARY

The Microbiome and Brain Health: What's the Connection?

Sarah R. Dash

Disclosures

March 24, 2015

In This Article

Promoting a Healthy Biome: Strategies

In both neurologic and psychiatric conditions, it is difficult to know what came first: the disorder, or the unhealthy gut. It is possible that gut dysbiosis is responsible for both disease risk and the severity of a disorder, but it is equally plausible that the stress associated with brain disorders is the principal driver of gut dysbiosis. Moreover, the same environmental risk factors (eg, unhealthy diet) may disrupt both gut and brain health.

It is clear that the causes and symptomology of some neurologic/neurodegenerative and psychiatric disorders have a similar underlying pathophysiology and that an unhealthy gut influences these through several overlapping pathways. Although it is difficult to tease out the individual contribution of each of these systems, given their complexity and the difficulty of isolating them clinically, the gut appears to be a key driver of a high-risk, inflammatory state in the body and brain and may prove to be the key in unlocking a new understanding of the etiology of brain diseases that supports new clinical and public health interventions.

Although gut microbial composition appears to be quite resilient, it is also readily modified. Lifestyle factors are particularly important to the composition, diversity, and stability of the gut microbiome. Below are several strategies that research suggests could contribute to overall gut health and that, in turn, may promote the health and protection of the brain.

Diet

There is good evidence for the role of individual nutrients, such as omega-3 fatty acids and zinc, in both physical and mental health; it is therefore useful to consume these nutrients as part of an overall healthful diet.

A healthful diet composed of fruits, vegetables, and whole grains has also been linked to higher levels of Bacteroidetes. These types of bacteria are particularly good at producing short-chain fatty acids, which help regulate gut inflammation.

Three main food components are proposed to benefit gut health: living microorganisms known as "probiotics" (found in such foods as yogurt, kefir, and kimchi); nondigestible carbohydrates (eg, dietary fiber found in fruits, vegetables, and whole grains); and secondary plant metabolites, such as flavonoids (found in brightly colored fruits, vegetables, and red wine).[33] Persons who consume a Western-style diet experience less of the protective benefits of plant foods and simultaneously provoke other metabolic disruptions through high fat and sugar consumption, which contribute to gut dysbiosis and inflammation.

Exercise

Evidence suggests that exercise may increase the diversity of bacteria living in the gut. One study[34] showed increased gut bacterial diversity and fewer markers of inflammation in athletes compared with controls. However, moderate exercise may be best; one study found that persons who exercised one to 30 times per month had higher levels of brain-protecting BDNF than nonexercisers or extreme exercisers.[35] Exercise has been shown to have positive anti-inflammatory benefits, which may promote both gut and brain health.[36]

Pre- and Probiotics and Fermented Foods

There is some support for the benefits of probiotic and prebiotic supplements and fermented foods within the gut, with some groups calling for the inclusion of probiotic or fermented foods in national food guide recommendations.[37] The anti-inflammatory benefits of fiber fermentation in the colon occur naturally during digestion of healthy, fiber-rich foods, resulting in metabolic by-products that include various vitamins and antioxidants.[38] Although some studies show promising results, larger, high-quality trials are needed to fully elucidate this relationship.

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