Discussion
Although the relationship between diet, the gut microbiota, host immunity and host metabolism is becoming more evident, the relationship between the microbiota and exercise has not been fully explored. Our findings show that a combination of exercise and diet impacts on gut microbial diversity. In particular, the enhanced diversity of the microbiota correlates with exercise and dietary protein consumption in the athlete group.
Diversity is important in all ecosystems to promote stability and performance. Microbiota diversity may become a new biomarker or indicator of health. Loss of biodiversity within the gut has been linked to an increasing number of conditions such as autism, GI diseases including IBD or recurrent Clostridium difficile-associated diarrhoea and obesity-associated inflammatory characteristics while increased diversity has been associated with increased health in the elderly. In this study, the diversity of the athlete gut microbiota was significantly higher than both control groups matched for physical size, age and gender. The proportions of several gut microbial taxa were also altered in athletes relative to controls. However, few differences were seen between the two control cohorts. Of note, the athletes and low BMI group had significantly higher proportions of the genus Akkermansia levels than the high BMI group. Akkermansia muciniphilla has been identified as a mucin-degrading bacteria that resides in the mucus layer and its abundance has been shown to inversely correlate with obesity and associated metabolic disorders in mice and humans. Everard et al recently showed that feeding Akkermansia, or restoration of Akkermansia levels by prebiotic treatment in diet-induced mice, correlated with an improved metabolic profile possibly due to enhanced barrier function. Interestingly, the athletes had lower inflammatory and improved metabolic markers relative to controls, and in particular the high BMI controls, demonstrating the enhanced health profile of this group. While the microbiota diversity of the two control groups did not differ significantly, it was noted that α diversity in the high BMI controls was numerically, although not significantly, lower than that of their low BMI counterparts. Reductions in the diversity of microbial populations in high BMI individuals has been reported in a recent study with a larger cohort size which also showed that dietary intervention can increase microbiota diversity in an obese cohort.
Rugby is a vigorous contact sport requiring considerable fitness and increased dietary requirements. The levels of plasma CK and creatinine were significantly elevated in the elite athlete group consistent with the high exercise loads.38–– Furthermore, diet was significantly different from that of controls, with increased intake of calories, protein, fat and carbohydrate. Diversity in the diet has been linked to microbiota diversity. In our study, microbiota diversity indices positively correlated with protein intake and CK suggesting that diet and exercise are drivers of biodiversity in the gut. The protein and microbiota diversity relationship is further supported by a positive correlation between urea levels, a by-product of diets that are rich in protein and microbiota diversity. Long-term diets have been linked to clusters in the gut microbiota with protein and animal fat associated with Bacteroides and simple carbohydrates with Prevotella. Fermentation of protein has also been suggested to result in the production of various potentially toxic products, such as amines and ammonia (NH3), and in one report, with growth of potential pathogens. In contrast, feeding of whey protein to mice mediates against the negative effects of a high fat diet. Indeed, in athletes, whey protein supplements represented a significant component of the protein intake in athletes but not controls. Whey protein has been associated with reductions in body weight and increased insulin sensitivity in the past and is frequently a major component of the athlete diet. Taken together, our results suggest that the relationship between exercise, diet and the gut microbiota warrants further investigation.
In conclusion, exercise seems to be another important factor in the relationship between the microbiota, host immunity and host metabolism, with diet playing an important role. Further, intervention-based studies to tease apart this relationship will be important and provide further insights into optimal therapies to influence the gut microbiota and its relationship with health and disease.