Effects of Athletic Nutritional Supplements on the Human Gut Microbiota: A Narrative Review

The human gut microbiota constitutes the microbial ecosystem within the human gut. It consists of trillions of mostly prokaryotic microorganisms living in the gut lumen, which have an active metabolic role in the regulation of many host functions, including vitamin synthesis and energy extraction from indigestible fiber. Host diet is the main driver of gut microbial composition and metabolic output. Athletes and athletic individuals often supplement their diet with legal nutritional supplements to enhance performance, especially at the elite level. This review summarizes and critically comments on key evidence of the effects of the most common athletic nutritional supplements on the human gut microbiota, based on the most recent literature. We cover suggested changes in bacterial diversity or the relative abundance of specific bacterial taxa and effects of nutritional supplementation on bacterial metabolism. We focus on the molecular pathways involved, we discuss contrasting results and inconsistencies, and we note limitations and challenges in the field. We conclude with a summary of evidence, proposals, and future directions.