Context: Lean body mass is essential for health, yet consensus regarding the effectiveness of protein interventions in increasing lean body mass is lacking. Objective: The aim of this systematic review was to evaluate the dose-response relationship of the effects of protein intake on lean body mass. Data Sources: The PubMed and Ichushi-Web databases were searched electronically, and reference lists of the literature included here and in other meta-analyses were searched manually. Study Selection: Randomized controlled trials evaluating the effects of protein intake on lean body mass were included. Data Extraction: Two authors independently screened the abstracts; 5 reviewed the full texts. Results: A total of 5402 study participants from 105 articles were included. In the multivariate spline model, the mean increase in lean body mass associated with an increase in protein intake of 0.1 g/kg of body weight per day was 0.39 kg (95%CI, 0.36-0.41) and 0.12 kg (95%CI, 0.11-0.14) below and above the total protein intake of 1.3 g/kg/d, respectively. Conclusions: These findings suggest that slightly increasing current protein intake for several months by 0.1 g/kg/d in a dose-dependent manner over a range of doses from 0.5 to 3.5 g/kg/d may increase or maintain lean body mass. Systematic Review Registration: UMIN registration number UMIN000039285.
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