Abstract
Objectives
Classic short-term nitrogen balance research estimated that the Recommended Dietary Allowance (RDA) of 0.8 g protein/kg/d would be adequate to maintain whole-body nitrogen balance in 97.5% of the population. However, achieving whole-body nitrogen balance does not necessarily equate with tissue-specific amino acid (nitrogen) needs, for example in skeletal muscle. The objective of this systematic review and meta-analysis was to assess in weight-stable adults the effects of chronically consuming greater than the protein RDA, compared to the RDA, on whole-body composition.
Methods
Articles published through 2018 were identified with PubMed, Scopus, Cochrane, and CINAHL databases. Five articles with 7 comparisons were identified to be relevant through the databases and through screening previous published reviews. Two researchers independently screened the articles for eligible randomized controlled trials (RCTs) of parallel design that measured changes in body composition after ³6 wk of dietary control.
Results
There was significant heterogeneity in the effect sizes amongst the comparisons (I2 = 72.8%, χ2 = 22.1, P = 0.001). Consuming greater than the protein RDA did not differentially affect any of the changes in total body mass [0.07 kg (−0.75, 0.88); WMD, (95% CI), Random effects], fat mass [−0.65 kg (−1.33, 0.03)], or lean body mass [0.08 kg (−0.59, 0.75)].
Conclusions
These results from controlled feeding RCTs support adequacy of the protein RDA to retain lean body mass and indicate that protein intakes greater than the RDA do not promote morphological changes among weight-stable adults.
Funding Sources
Purdue University Graduate Lynn Fellowship. No external funding was provided for this review.