Abstract

Objectives To investigate the effects of probiotic supplementation on mood state, mood-related biochemical indicators, and gut microbiota in combat athletes undergoing pre-competition rapid weight loss. Design A randomized, placebo-controlled intervention study. Methods Thirty-two combat athletes undergoing pre-competition rapid weight loss were randomized to a probiotic group (PRO) or a placebo group (PLA). One participant in the PRO group withdrew during the intervention; thus, 32 athletes completed the study and were included in the final analysis (PRO, n = 16; PLA, n = 6). The PRO group received a proprietary multi-strain probiotic powder for 4 weeks, while the PLA group received a matched placebo. Mood state, circulating biochemical indicators, and gut microbiota composition were assessed before and after the intervention. Results The percentage of body weight reduction was comparable between groups. Before false discovery rate correction, the clearest mood-related signal was observed for the fatigue subscale of the Profile of Mood States, with fatigue increasing in the PLA group but decreasing in the PRO group. At the biochemical level, circulating gamma-aminobutyric acid showed a greater increase in the PRO group than in the PLA group. Probiotic supplementation was also associated with the modest taxonomic shifts in the gut microbiota, including numerical increases in Firmicutes, Blautia , and Faecalibacterium and a decrease in Streptococcus , whereas alpha- and beta-diversity did not differ significantly between groups. In targeted exploratory correlation analyses, Firmicutes was positively correlated with circulating gamma-aminobutyric acid at the phylum level after false discovery rate correction. However, after false discovery rate correction, none of the questionnaire or biochemical interaction effects remained statistically significant. Conclusions In combat athletes undergoing pre-competition rapid weight loss, probiotic supplementation was associ