Exercise your gut (microbiome)

As a neuroscientist who studies the effects of exercise on brain functioning, I am ultimately interested in the connection between the body and brain. At a recent scientific conference on learning and memory, Dr. Monika Fleshner of the Department of Integrative Physiology at the University of Colorado, spoke about an exciting area of research that truly connects the body and brain: the gut microbiome. I was well aware of the enteric nervous system, which is a part of the autonomic nervous system that lines the digestive tract (from esophagus to colon), and its connection to how we think and feel. My dance professor Andrea Olsen in her book The Place of Dance: A Somatic Guide to Dance and Dance Making calls this the “brain in the gut.” However, I was less aware of the diverse bacteria (i.e., the microbiota) in our gut that significantly impacts the functioning of our brain. Scientists and physicians are becoming increasingly aware of the impact of gut microbiota on overall physical and mental wellbeing, and it turns out that exercise is one way to improve the health of the gut microbiota [1].

The gut microbiota are bacteria or microorganisms living inside our intestinal tract that aid very generally in digestive processes. In each of us, there are approximately 100 trillion of these microorganisms with at least 1,000 different known species. Similar to a fingerprint, the diversity of our gut microbiota is another thing that makes each of us unique [2].

Along with digestive processes, the microbiota interact with and affect the immune system, especially during the early stages of development [3]. When dysregulation of the gut microbiota occurs, problems can ensue such as inflammatory bowel disease, obesity, diabetes, and some report even neuropsychological disorders like anxiety and depression and developmental disorders like autism.

Amazingly, the gut microbiome acts like an endocrine gland. That is, it secretes substances that influence the body and the brain. These include the main inhibitory neurotransmitter GABA (gamma-aminobutyric acid) as well as the neurotransmitters dopamine, serotonin and norepinephrine [4]. Additionally, work in rodents shows that direct administration of certain strains of gut microbiota causes decreased levels of anxiety and depression as well as specific changes in the brain. These facts have led scientists to believe that the gut microbiota directly effects how the brain functions. Additionally, as is highlighted in the New York Times blog by Peter Andrey Smith, Can the bacteria in your gut explain your mood? (http://www.nytimes.com/2015/06/28/magazine/can-the-bacteria-in-your-gut-explain-your-mood.html?_r=0), certain of the gut microbiota are associated with symptoms in depressed patients and Dr. Mark Lyte even points to the idea of “psychobiotics” or prescribing gut microbiota to help symptom improvement in psychiatric disorders.

Before “psychobiotics”, it appears that we can do something else to help improve the health of the gut microbiota – exercise [5]. For example, research has shown that exposing rodents to voluntary wheel running helps to improve the composition of the gut microbiota, with rats that run the greatest distances showing the lowest levels of harmful bacteria [6]. Exercise even helped to reverse the negative influence of a high fat diet on the gut microbiome as well as improve gut microbiota diversity in animal models of obesity and hypertension [7, 8]. For the first time, a recent study showed that this relationship is also true in humans. Clarke and colleagues assessed the diversity of the gut microbiota in 40 athletes (male elite professional rugby players) and 46 controls (non-athlete males with similar body mass index levels). As with the exercising rodents, athletes had a significantly healthier gut microbiota composition, however, this relationship was heavily influenced by protein consumption in the athletes [9].

Collectively, this work shows that the gut microbiota can be influenced by lifestyle choices including exercise and diet, which in turn influence physical and mental health. As a scientist, it is exciting to learn that we are still uncovering new ways that exercise changes our bodies and brains, and as a person who loves to exercise, I find this quite empowering. Much more research is warranted in this area, and future longitudinal studies will need to investigate the influence of increased exercise on gut microbiota diversity and its relationship to changes in mood and cognition. Importantly, future studies should examine how cardiopulmonary fitness (VO2 max) relates to gut microbiota diversity.

References:

1. Bermon, S., et al., The microbiota: an exercise immunology perspective. Exerc Immunol Rev, 2015. 21: p. 70-9.

2. Qin, J., et al., A human gut microbial gene catalogue established by metagenomic sequencing. Nature, 2010. 464(7285): p. 59-65.

3. Hooper, L.V., D.R. Littman, and A.J. Macpherson, Interactions between the microbiota and the immune system. Science, 2012. 336(6086): p. 1268-73.

4. Barrett, E., et al., gamma-Aminobutyric acid production by culturable bacteria from the human intestine. J Appl Microbiol, 2012. 113(2): p. 411-7.

5. Peters, H.P., et al., Potential benefits and hazards of physical activity and exercise on the gastrointestinal tract. Gut, 2001. 48(3): p. 435-9.

6. Evans, C.C., et al., Exercise prevents weight gain and alters the gut microbiota in a mouse model of high fat diet-induced obesity. PLoS One, 2014. 9(3): p. e92193.

7. Kang, S.S., et al., Diet and exercise orthogonally alter the gut microbiome and reveal independent associations with anxiety and cognition. Mol Neurodegener, 2014. 9: p. 36.

8. Petriz, B.A., et al., Exercise induction of gut microbiota modifications in obese, non-obese and hypertensive rats. BMC Genomics, 2014. 15: p. 511.

9. Clarke, S.F., et al., Exercise and associated dietary extremes impact on gut microbial diversity. Gut, 2014. 63(12): p. 1913-20.