To increase strength and lean body mass, protein has become one of the most popular supplements among athletes. The aim of this study was to analyze the effect of protein supplementation on body composition. A systematic review of the randomized controlled trials (RCT), published in MEDLINE/PubMed and SciELO up to April 10, 2009, was conducted. All RCT conducted in healthy subjects with interventions of six or more weeks were included. Nine studies fulfilled the inclusion criteria, and three of them had level 3 of evidence. Among these studies, the increase of lean mass ranged from 0.8 to 1.9 kg. However, the study with the longest term had duration of 12 weeks. Therefore, the evidence does not support the recommendation for the consumption of protein supplements among healthy individuals.