The effects of GG supplementation on gastrointestinal and respiratory outcomes: a systematic review and meta-analysis of randomized controlled trials.

GG (LGG) supplementation has demonstrated efficacy in reducing diarrhea duration in children. However, its preventive potential and broader therapeutic applications beyond pediatric diarrhea remain less well characterized. A systematic review and meta-analysis were performed to investigate the efficacy of LGG supplementation on the risks of composite (including infections and symptoms) gastrointestinal (GI) and respiratory outcomes, as well as the duration of relevant symptoms. The protocol was pre-registered in the PROSPERO database (CRD42024539944). The PubMed, Web of Science, and Cochrane databases were searched for relevant articles. A random-effects model was applied to generate pooled relative risks (RRs) or weighted mean difference (WMD) estimates with 95% confidence intervals (CIs). Sixty-nine trials were included. LGG supplementation reduced the risk of composite GI outcomes (RR 0.88, 95% CI 0.81, 0.96; = 38), primarily through a reduction in diarrhea risk (RR 0.64, 95% CI 0.52, 0.77; = 24) and, to a lesser extent, taste disturbances (RR 0.40, 95% CI 0.22, 0.72; = 5). Other GI outcomes-including vomiting ( = 13), nausea ( = 9), abdominal pain ( = 12), bloating ( = 8), constipation ( = 8), stomach rumbling ( = 3), and loss of appetite ( = 5)-showed limited effect. Respiratory outcome risk was also lower (RR 0.86, 95% CI 0.78, 0.94; = 23), largely attributable to reduced respiratory infection risk (RR 0.87, 95% CI 0.79, 0.97; = 18), with limited effects on respiratory symptom risk ( = 7). LGG supplementation shortened GI symptom duration (WMD -0.62, 95% CI -0.81, -0.44 days; = 33), largely attributable to reduced diarrhea duration (-0.83, 95% CI -1.06, -0.59 days; = 29), with limited effects on vomiting duration ( = 6). LGG had limited effects on respiratory symptoms ( = 6). Moderate-to-high heterogeneity was observed for the aforementioned outcomes, except GI outcomes other than diarrhea and GI symptom risk. Prediction intervals supported consistent benefits for diarrhea outcomes but frequently crossed the null for others, indicating greater uncertainty. Effects on diarrhea outcomes and respiratory infection risk were more consistent in children; evidence in adults was limited. Certainty was rated moderate for diarrhea outcomes and mostly low for others. LGG supplementation reduces diarrhea risk and duration in children, supported by moderate-certainty evidence and consistent effects across trials. Other outcomes showed more variable results, reflecting limited or inconsistent evidence. These findings support LGG's role in pediatric diarrhea management and prevention while underscoring the need for high-quality trials to clarify broader clinical applications.