The current review aimed to elucidate the modulatory effects of physical activity and sports activities on the gastrointestinal microbiome. Twenty cross-sectional and longitudinal studies were analyzed, using metagenomic and various omics measures. Studies across gut microbiota and exercise have recently been published, mainly examining the effects of training programs in subjects who did not previously perform regular physical activity. These studies suggest that exercise does not cause structural changes in the microbiota, with species diversity remaining unchanged after 6 weeks or less of engaging in an exercise program. Gut cosystem adaptation to exercise in sedentary subjects has been reported to respond to the host phenotype (body mass index and age). Results suggests that cross-sectional studies can provide insights into differences between highly adapted athletes with active lifestyles and sedentary adults, particularly in the abundance and function of gut microbiota. Interestingly, comparing healthy adults with different levels of cardiorespiratory fitness has revealed similar results, indicating a lack of important differences in the abundance of taxonomic groups and species richness. Metabolomic, metagenomic and transcriptomic approaches allow the identification of possible mechanisms between the intestinal microbiota and the host physiology in physical exercise, mainly through functional groups of bacteria such as Veillonella, Prevotella, Akkermansia and archaeon Methanobrevibacter. Most of the reviewed research focused on endurance training. Thus, the potential effects of resistance training and high-intensity training on the gastrointestinal microbiome need to be explored in future studies.
