Dietary Plant Saponins and Exercise-Induced Fatigue: Structural Characteristics, Bioavailability, Efficacy, Physiological Mechanisms, and Implications for Functional Foods

Background: Exercise-induced fatigue involves a task-dependent reduction in the capacity to sustain physical performance, an increase in perceived fatigue during or after exercise, or both. Dietary plant saponins are amphiphilic glycosides widely distributed in edible plants and botanical preparations, but evidence regarding their effects on exercise-related fatigue remains heterogeneous across food chemistry, exercise physiology, and pharmacological research. Scope and approach: This narrative review critically evaluates dietary plant saponins using a composition–exposure–outcome framework. The framework links botanical source and processing history with structural and chemical definition, gastrointestinal transformation and systemic exposure, and clearly defined exercise-related outcomes. Human, animal, and mechanistic evidence are considered separately according to exercise-related outcome domain, and principal human trials are qualitatively appraised for randomization/blinding, sample size/attrition, outcome selection, and potential bias, with emphasis on distinguishing preparation-level effects from evidence attributable to individual saponins. Key findings and conclusions: Preclinical studies of saponin-rich preparations have reported improvements in exercise duration, glycogen-related indices, lactate-related measures, and changes in mitochondrial, inflammatory, or redox-associated markers. Human evidence remains limited and includes both preparation-level findings and emerging compound-specific evidence from purified ginsenoside Rg1; however, the available Rg1 trials are small, predominantly acute, and require independent replication. Preparation-level evidence is available for Panax ginseng, Gynostemma pentaphyllum, and Panax notoginseng, whereas controlled Tribulus terrestris trials have not demonstrated consistent ergogenic effects. Current evidence does not support a simple structure–activity relationship based solely on total-saponin content, sugar-chain number, aglycone class, or stereochemistry. Instead, processing-dependent composition, gastrointestinal deglycosylation, microbial transformation, and systemic exposure must be considered together when interpreting biological responses. The major unresolved question is therefore not whether saponins influence fatigue-related pathways, but whether chemically defined preparations achieve biologically relevant exposure levels that reproducibly improve prespecified exercise outcomes. Future studies should integrate compositional standardization, parent and metabolite exposure assessment, physiologically meaningful exercise endpoints, and food-format feasibility.