The effect of glutamine supplementation on athletic performance, body composition, and immune function: A systematic review and a meta-analysis of clinical trials

Summary Background & aim This systematic review and meta-analysis of available evidence was conducted to obtain a conclusive result on the effects of glutamine supplementation on athletes. Methods Systematic review and meta-analysis. Data related to body mass, lean body mass, body fat percentage, Vo2 max, lymphocytes, leukocytes and neutrophil counts were extracted to determine the effects of GLN on performance outcomes. Data Sources The literature search was conducted across the databases Pubmed, Scopus, ISI Web of Science, SID (Scientific Information Database) and Cochrane Central Register of Controlled Trials, covering a period up to January 2017. Eligibility Criteria for Selecting Studies Clinical trials evaluating glutamine supplementation outcomes on athletes aged over 18 were included. Results A total of 47 studies were included in the systematic review, and 25 trials matched the inclusion criteria for the meta-analysis. According to the meta-analysis, glutamine has a significant effect on weight reduction (WMD = −1.36 [95% CI: −2.55 to −0.16], p = 0.02). Moreover, neutrophil numbers were reduced following glutamine intake at doses greater than 200 mg/kg body weight (WMD = −605.77 [95% CI: −1200.0 to 52.1]; P = 0.03). Also, supplementation by glutamine dipeptide resulted in higher blood glucose after exercise (WMD = 0.51 [95% CI: 0.18, 0.83] mmol/l; P = 0.002). There was no association between glutamine ingestion and other outcomes investigated. Conclusion According to this meta-analysis, generally, glutamine supplementation has no effect on athletics immune system, aerobic performance, and body composition. However, the current study showed that glutamine resulted in greater weight reduction. In addition, the present study suggests that the efficacy of glutamine supplementation on neutrophil numbers could be affected by supplement type and dose.