GLOSSARY

Fecal Metabolites are stool chemicals of varied origin, whose remainder does not equal total production or absorption.

Microbial metabolites are products or intermediates of microbial activity, sometimes further modified by the host. Not all are uniquely microbial: hosts also produce lactate and succinate. Location, amount and pathway determine interpretation. A metabolome describes measured chemicals rather than the living community. Detecting a compound without suitable methods does not establish its exact origin or a definite beneficial or harmful effect on the athlete.

Composition identifies detected groups; functional potential concerns genetic capacity, while activity concerns what is actually expressed or produced. Different communities can share functions. A gene's presence does not guarantee a particular metabolite output. Organism names alone therefore establish neither extra usable energy nor improved absorption, strength or recovery. Distinguish taxonomic detection, measured activity and meaningful human outcomes when assessing a microbiome claim.

For sports use, do not jump from a mechanism to a definite performance effect; evaluate food, training, tolerance and actual goal-related change together rather than ending assessment at one marker.

One microbe's product can feed another; some use lactate or acetate within networks producing other metabolites. Cross-feeding makes community effects more complex than adding individual abundances. Lactate and succinate are not merely useless waste. However, identifying a laboratory pathway does not itself show that supplementing its intermediate or manipulating the community improves athletes. Net output depends on production, consumption and the organisms actually present in context.

Microbes use colonic substrates including carbohydrate and protein products, producing different metabolites. Substrate amount, transit and community composition influence the routes. Protein fermentation does not make every protein meal harmful, and carbohydrate fermentation is not symptom-free at every dose. Sports diets should coordinate adequate protein, plant foods and tolerance rather than judging a whole nutrient solely by one fermentation product or eliminating needed recovery food.

Fecal short-chain fatty-acid concentration reflects production, microbial use, absorption and water dilution, not total production rate. Low values have multiple interpretations, and high values are not always better. Define sample and method. Read stool measurements alongside diet and function rather than diagnosing muscle-fuel shortage or prescribing purified acids from one value. Concentration, flux and physiological effect are distinct quantities even when reported for the same compound.

An association between microbes and health or performance does not alone establish microbial causation. Diet and training can influence both, and culture or animal findings are not direct human prescriptions. Sports-benefit claims need relevant human outcomes for the actual intervention. An axis name or biological pathway cannot replace evidence of a practical effect, especially when a product is marketed using results from a different population or formulation.