Bugs and the brain: The emerging science of psychobiotics

July 2015

BY VICTOR S. SIERPINA, MD, ABFM, ABIHM, Director, Medical Student Education Program, WD and Laura Nell Nicholson Family Professor of Integrative Medicine, Professor, Family Medicine University of Texas Distinguished Teaching Professor

 For some time, I have been following and reporting on the research on the wide spectrum of effects of the microbiome, the bacteria in our gut. This six pound mass of microscopic organisms is essential to digestion as they help us break down cellulose and other plant and animal matter that our bodies cannot digest on their own. They are thought to protect us from a broad spectrum of diseases. These include conditions including related to inflammation, immunity, allergy, obesity, diabetes, heart disease, and cancer. That being said, the science of the study of the microbiome is still in its infancy with more information available in laboratory conditions than in human health and disease. Nonetheless, there is substantial interest at UTMB and other research centers in translating the basic science of microbiome genes, chemistry, and in animal models like mice to humans. I predict that the studies of probiotics/psychobiotics will have a similar large effect on human health as the discovery of antibiotics.

One surprising area of the impact of the microbiome that has been recently discovered are the effects of gut bacteria on the brain and behavior. There has been speculation for some time that gut bacteria alterations might be affecting the health of children with conditions like autism spectrum and ADHD. Dr. David Perlmutter, a researcher on innovative therapies in neurology recently reported on a case of severe autism that responded to fecal transplantation. A healthy 14-yearold offered stool samples, which were infused several times into a severely autistic child who began after about seven infusions to speak and interact in a normal way. Perlmutter proposed was that the bacteria in his gut were secreting propionic acid and possibly other neurotoxic chemicals. While this unique treatment definitely needs replication and should not be a call for desperate parents to try to re-inoculate the gut of their affected autistic children with bacteria from healthy donors, it does raise the question of how gut bacteria could possibly be part of the gut-brain axis. More research is clearly needed. Are such conditions brain problems or gut problems? This is a provocative medical and scientific question.

A recent New York Times magazine synopsized several recent studies done primarily on mice found correlations between their gut bacteria and behavior such as markers of anxiety. Mice are not men, but the physiology suggested by these studies was fascinating. Did you ever have a “gut feeling” about something? Of course, you have and this is just a simple parallel on how our gut contains so many psychoactive chemicals that we may affect our moods and behavior.

Serotonin, which is the neurotransmitter most involved in the treatment of depression, anxiety, and other psychiatric conditions, is found in very high levels in our gut. It can be affected by how we eat, our stress levels, and yes, by the array of bacteria in our gut. Other gut neurotransmitters included dopamine and gamma-aminobutyric acid (GABA). Xanax and Valium, anti-anxiety medications work through pathways related to this transmitter. Stressed mice did better when their gut was infused with certain probiotics acted more relaxed compared to those with usual gut bacterial profiles. They behaved “as if they were on Prozac” according to the researcher, Dr. John Cryan. Another researcher, Dr. Mark Lyte from Abilene, Texas, and now in Iowa, faced strong headwinds in the research community when he proposed the same idea, that gut bacteria could affect our moods. Though he was one of the first to advocate the concept of psychobiotics, he advises caution in rushing to overly broad conclusions and therapies until more science is done in the area.

If a primary actor in our gut is our microbiome, it is not a great stretch to postulate how their activity and the ways they affect metabolism, create chemical products, impact neurotransmitter release, and so on may have a significant effect on our brains, mood, and behavior. One question is could altering our gut bacteria replace some of our psychiatric drugs and therapies?

It turns out we can affect the kinds and numbers of various bacteria in our gut. Healthier gut bacterial profiles include:

• Eating more prebiotics that are largely plant-based fibers. Prebiotics are carbohydrates that cannot be digested by the human body and are food for probiotics. They include foods like whole grains, bananas, onions, garlic, honey, and artichokes.

• It turns out that being vaginally birthed and breast fed improves the healthy profile of gut bacteria in children.

• Eating probiotics like yogurt or other fermented foods should be a regular part of our diet.

• Replacing our gut bacteria with healthy probiotics after they have been altered by antibiotics, chemotherapy, steroids, and other medical interventions.