The gut microbiome has been a hot topic in the scientific literature, crossing many disciplines. Because gut microbiota can affect exercise performance, it will be the topic of discussion for this Nutritionist’s View column.
WHAT IS THE GUT MICROBIOTA?
The gut microbiota in humans consists of 10 to 100 trillion interrelated bacterial cells in the intestine. The genes that these cells house are what comprise the human microbiome (6). The term, human microbiome, was created by Lederberg and McCray (3) in 2001. Although the terms microbiota and microbiome are distinctly different, they often are interchanged.
Although Lederberg and McCray (3) created the term human microbiome, studies of the multiplicity of the human microbiome began in the 1680s, with Antonie van Leewenhoek (8), who reported the significant differences between his oral and fecal microbiota. Although the differences between oral and fecal microbiota are important, more important are the differences that van Leewenhoek reported between them in health and disease among different individuals. However, why these differences exist, which could lead to methods of treatment for disease states, is perhaps even more important (7).
GUT MICROBIOTA AND EXERCISE STRESS
Although it has been well established that exercise can prevent chronic disease, such as heart disease and some cancers, it also is a stressor to the body. In particular, athletes of all types can experience less-than-optimal performance, fatigue, and mood alterations as a result of intense training (1). High-intensity training can lead to a stress response, which in turn stimulates the sympathetic-adrenomedullary axis and hypothalamus-pituitary-adrenal axis (1). Briefly, the sympathetic-adrenomedullary axis produces the neurotransmitters norepinephrine and epinephrine, resulting in increases in heart rate. The hypothalamus-pituitary-adrenal axis is the hormonal response to stress. The pituitary gland produces the hormone adrenocorticotropic hormone, whereas the adrenal cortex (within the adrenal glands) produces cortisol. Because exercise is a stressor, there may be a significant association between exercise and alterations in the composition of the gut microbiota (1).
It has been reported that dietary intake can significantly change the composition of the gut microbiota. In addition, it has been reported that the gut microbiota may act similarly to an endocrine organ; that is, secreting compounds from the gut that will work in another part of the body. In addition, the gut microbiota may regulate the hypothalamus-pituitary-adrenal axis in athletes (1). Clark and Mach (1) state, “…targeting the microbiota therapeutically may need to be incorporated in athletes’ diets that take into consideration dietary fiber as well as microbial taxa not currently present in athlete’s gut.”
O’Sullivan et al. (5) examined the dietary intake and exercise on the gut microbiota in the Irish International rugby football team before World Cup training. The researchers evaluated dietary intake and pattern (via food frequency questionnaires), fecal microbiota, body composition, and pro- and anti-inflammatory cytokine and creatine kinase concentrations. Creatine kinase concentrations were used as markers for intensity of exercise training. The researchers compared the rugby players to two groups of healthy controls with varying physical activity levels and body mass index. Not surprisingly, the rugby players had a lower percent body fat and higher lean body mass than the control participants. In addition, the rugby players consumed multiple meals throughout the day; however, the control participants consumed meals at usual meal times. With respect to dietary intake, the rugby players consumed significantly more carbohydrates, protein, fat, sugar, cholesterol, and saturated fat per day than both control groups. Although the rugby players exercised more intensely than the control groups, they still had lower concentrations of inflammatory cytokines than the control groups. Furthermore, the rugby players had an increased fecal microbiota multiplicity compared with the control groups. O’Sullivan et al. (5) reported that protein intake and creatine kinase concentrations (e.g., intense exercise) correlated with diversity in gut microbiota (Figure). The researchers stated that their results need to be taken with caution because they were correlational and not cause-effect. Although these results represent an association, they provide strong evidence that intense exercise and dietary intake can significantly affect the gut microbiome, and likely, exercise performance.
The gut microbiota also can affect the brain. Thus, the effects of exercise on the gut microbiota can lead to positive effects on cognition and/or emotion (9).
In addition to the effects of exercise and diet on the gut microbiota, and, in turn, the effect on the brain, there is evidence that the gut microbiota can play an important role in the body’s antioxidant defense system. Thus, Hsu et al. (2) examined the relationship between gut microbiota and exercise performance in specific pathogen-free, germ-free, and Bacteroides fragilis gnotobiotic mice. They reported greater concentrations of glutathione peroxidase and catalase (antioxidant enzymes) in the specific pathogen-free and B. fragilis gnotobiotic mice compared with the germ-free mice. Although the researchers conducted this study in mice, it demonstrates the possible connection among exercise, gut microbiota, and the antioxidant defense system in athletes.
In addition to the effects that exercise can have on the gut microbiota, in a review paper, Mach and Fuster-Botella (4) stated that the gut microbiota also may be an effective assessment of athletes’ immune status, stress resulting from intense exercise, and metabolic conditions. The authors also stated “…that modifying the microbiota through the use of probiotics could be an important therapeutic tool to improve athletes’ overall general health, performance, and energy availability while controlling inflammation and redox [oxidation-reduction] levels” (4).
This Nutritionist’s View column was meant to pique your interest in gut microbiota, diet, and exercise. Although I addressed only a few research studies, they provide evidence of the importance of diet and exercise on the gut microbiota, and subsequently, how that affects the brain and antioxidant enzyme defense system. The effects on the brain can lead to better cognitive performance for athletes. An improved antioxidant defense system can result in better recovery and repair postexercise. It also is clear that more research in the area of diet, exercise, and the gut microbiota is required to provide us with more answers on their relationships.
1. Clark A, Mach N. Exercise-induced stress behavior, gut-microbiota-brain axis and diet: a systematic review for athletes. J Int Soc Sports Nutr
2. Hsu YJ, Chiu CC, Li YP, et al. Effect of intestinal microbiota on exercise performance in mice. J Strength Cond Res
3. Lederberg J, McCray A. Ome sweet ’omics: a genealogical treasury of words. The Scientist
5. O’Sullivan O, Cronin O, Clarke SF, et al. Exercise and the microbiota. Gut Microbes
6. Turnbaugh PJ, Ley RE, Hamady M, Fraser-Liggett CM, Knight R, Gordon JI. The human microbiome project. Nature
7. Ursell LK, Metcalf JL, Parfrey LW, Knight R. Defining the human microbiome. Nutr Rev
. 2012;70(Suppl 1):S38–44.
8. van Leeuwenhoek A. An abstract of a letter from Antonie van Leeuwenhoek, Sep. 12, 1683. About animals in the scurf of the teeth. Philos Trans R Soc Lond
9. Yuan TF, Ferreira Rocha NB, Paes F, Arias-Carrión O, Machado S, de Sá Filho AS. Neural mechanisms of exercise: effects on gut miccrobiota and depression. CNS Neurol Disord Drug Targets