Kazemi A, Speakman JR, Soltani S, et al. - Researchers determined how IGF-1 in humans is altered by calorie restriction (CR) or increase in protein intake. Based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement guidelines, the systematic review protocols were used. They explored PubMed, SCOPUS and ISI Web of Science databases for the relevant studies. The inclusion criteria were met by 12 studies, including 8 clinical trials and 4 observational studies, in the meta-analysis of the calorie restriction studies. Findings revealed no association of CR with a significant alteration in circulating IGF-1 in humans. However, increased levels of circulating IGF-1 were detected in correlation with an increase in protein intake.