Combat sports athletes, such as boxers, judoka and mixed martial artists, often experience gastrointestinal disturbances during pre-competition weight management.
Common weight-cutting strategies include intensified training loads, restricted energy intake, reduced fluid intake, and increased dehydration. Studies have shown that these methods can cause serious health issues, including depletion of glycogen stores, electrolyte imbalances, acute kidney injury, and severe cognitive impairment.
Although these health risks are now getting more attention in sports medicine, current discussions often overlook the gastrointestinal system.
A study by researchers in Shanghai aimed to investigate the effects of probiotic supplementation on gut barrier function in combat athletes undergoing rapid weight loss before competition.
Twenty-four elite male athletes were randomized to receive either a multi-strain sports probiotic (1.5 × 1010 CFU, two sachets daily) or placebo for 4 weeks.
Each sachet contained a 2g dose comprising Lactobacillus rhamnosus R0011, Lactobacillus swissi Lafti L10, Lactobacillus salivarius HA-118, Lactobacillus plantarum Lp-G18, Lactobacillus swissi R0052, Bifidobacterium animalis Lafti B94, and Bacillus coagulans GBI-306086.
Results showed that probiotic supplementation significantly reduced gastrointestinal symptoms, including dyspepsia, diarrhea and constipation, as well as gut permeability markers, including zonulin, intestinal fatty acid-binding protein (I-FABP) and D-lactate, compared to placebo.
Additionally, the probiotic group showed a greater increase in secretory immunoglobulin A (SIgA) levels, whereas the placebo group had larger increases in calprotectin and inflammatory markers.
The study also found that the intervention enriched beneficial butyrate-producing bacteria Blautia and Latilactobacillus while suppressing pathogenic Streptococcus.
“These findings demonstrate that probiotic supplementation serves as a safe, effective nutritional strategy to maintain gut homeostasis during rapid weight loss in combat athletes,” the researchers wrote.
Less gut permeability, inflammation
The study also reported improvements in gut permeability and inflammation in the probiotic group, as seen in a reduction in gut permeability markers, including zonulin and intestinal fatty acid-binding protein (I-FABP).
Plasma levels of I-FABP, for example, serve as a direct biomarker for intestinal mucosal damage and cellular breakdown associated with gut permeability and it typically rises during acute heat stress or dehydration.
In contrast to the probiotic group, the placebo group reported an absence of significant alterations in plasma FABP levels.
Zonulin — a regulator of the intestinal barrier by loosening intercellular tight junctions—was also significantly reduced by probiotic intervention in this study. This is consistent with the findings of a previous study on multi-strain probiotics.
Notably, post-intervention zonulin levels in both groups remained above the upper limit of the healthy reference range (above 40ng/ml), suggesting that elite athletes may experience chronically elevated intestinal permeability due to prolonged training loads.
While probiotics mitigate this damage, complete restoration may require longer intervention periods, according to the researchers.
At the same time, the increased levels of the antibody secretory immunoglobulin A (SIgA) in the probiotic group also indicated a reinforced immune barrier or an active prevention of pathogen adhesion.
“We hypothesize that the improvement in barrier function was due to the increase in SIgA secretion, but in the absence of significant correlations between SIgA and gut microbiota composition after FDR (false discovery rate) correction, a direct causal role for SIgA cannot be inferred,” the researchers wrote. “The observed enhancement of intestinal barrier function is more plausibly linked to probiotic-induced modulation of butyrate-producing microbiota.”
Therefore, they suggested that future research could optimize strain selection, dosing regimens, and intervention timing, while integrating hydration biomarkers to further elucidate the underlying mechanisms.
Source: Frontiers in Nutrition. doi: doi.org/10.3389/fnut.2026.1857878. “Effects of probiotic supplementation on gut barrier function in combat athletes during pre-competition weight loss”. Authors: Jing Wang, et al.
