GLOSSARY

Vagus Nerve is an important visceral-brain nerve, not the whole axis or a vessel carrying every metabolite.

Gut-brain communication is bidirectional through neural, immune, hormonal and metabolic routes; the vagus is one pathway. Peripheral gut serotonin does not directly substitute for brain serotonin, and microbial neurotransmitter production does not guarantee equivalent brain delivery. Mood or cognitive claims need human evidence. Psychobiotic is a research-related term, not an automatic replacement for treatment or adequate sleep, and effects must be assessed for the actual intervention and outcome.

Tryptophan enters host pathways such as kynurenine and serotonin metabolism as well as microbial routes. Some microbes produce indole derivatives with molecule- and context-specific effects. Kynurenine should not simply be labeled a bacterial product. Receptor and animal findings are informative but do not alone justify tryptophan or derivative supplementation for mood, intestinal health or performance. Distinguish biochemical possibility from a tested human intervention and its dose.

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.

Gut-muscle, liver, bone or adipose axes describe interaction frameworks rather than one proven pathway with a universal prescription. Metabolites, immune signals and nutrition may mediate them. Some evidence comes from animals or human associations, distinct from trials demonstrating benefit. Food and recovery remain foundational for athletes. A gut-muscle-axis product still requires evidence for its own formulation instead of borrowing a mechanistic label to claim greater strength or muscle mass.

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.

Microbial responses to food, training or supplements vary between people and depend on baseline and timing within a person. Useful personalization begins with a goal, history and response assessment; one commercial report does not provide an established precise menu. Athletes should assess performance, tolerance and adequate food alongside data. Resembling a reference population alone is not success if practical outcomes or nutritional adequacy do not improve.

Gut health includes absorption, bowel function, barrier performance and absence of concerning symptoms, not one organism or health score. Different communities can coexist with satisfactory function. Varied food, adequate energy and attention to recurring symptoms provide practical foundations. Athletes also need comfort during sessions and the ability to meet fueling needs, assessed over time with general health rather than replaced by a single microbiome number or supplement-driven target.