2.1. Participants
A total of 30 male university student-athletes from Beijing Sport University were recruited. The subjects had practiced football for 9.87 ± 0.58 years, and 86.7% of them were first-class players. The subjects were randomly assigned to the prebiotic group (PG) or synbiotic group (SG). During the experiment, the subjects maintained their normal diet. They ate at a fixed location. All subjects trained daily, with no change in schedule. The average training duration was more than 11 h/week (i.e., a high-intensity training load) [