Protein and amino acid supplementation in sport

Objective: To perform a literature review of the current available data on protein and amino acid supplementation in sports, their efficacy and safety. Data sources: The search was limited to English language citations published in the years 1980-2007. MEDLINE and PubMed searches were performed in March 2007 on all studies using the Mesh terms: proteins, amino acids, supplement, the desired supplement name and sports/ exercise. Study section: Initially, only randomised controlled clinical trials were included in the analysis. In addition, several recent reviews and relevant meta-analyses were used. Data extraction: A title scan was performed to exclude references that did not include protein supplementation, exercise, or the population's health status was abnormal. Relevant literature was identified, sourced, and reviewed and the selected manuscripts are cited. Data synthesis: Although protein supplementation has been widely discussed in the literature for many years, it was surprising to find the relatively low number of randomised controlled trials that met the inclusion criteria for this review. When the general terms "protein/ amino acids" were used, 43 citations met the criteria; "creatine" yielded 53 citations; "glutamine" 2 citations, and β-hydroxy-β-methylbutyric acid (HMB)" 9 citations. The bulk of the data suggests that protein requirements are usually met by an iso-caloric, balanced diet, for both endurance and resistance training. Supplementing the athlete's diet with protein or amino acids has not proven beneficial and may even sometimes be harmful. Creatine is currently the only product that has clear scientific support to enhance sporting performance. The timing of protein supplementation may be an important factor in trying to achieve anabolic effects. Conclusions: The use of protein supplements for the healthy, non-competitive adult engaged in recreational sports is usually not warranted. There are only limited data to support protein supplementation in competitive sports. There is some evidence supporting the use of creatine and possibly HMB as ergogenic aids in specific situations. Further research is needed before definitive recommendations can be made on the type, timing and effectiveness of protein supplements.