A systematic review, meta-analysis and meta-regression of the
effect of protein supplementation on resistance traininginduced
gains in muscle mass and strength in healthy adults
R.W. Morton Appl. Physiol. Nutr. Metab. Vol. 42, 2017
A systematic review, meta-analysis and meta-regression were performed
to determine if dietary protein supplementation augmented
resistance exercise training- (RET) induced gains in muscle mass and
strength. Medline, Embase, CINAHL and SportDiscus were searched
systematically for randomized controlled trials with RET ≥6 wk in
duration and dietary protein supplementation. Random-effects metaanalyses
and meta-regressions were performed with a priori determined
covariates related to protein intake and relevant RET program
variables. Unadjusted segmental regression analysis was used to determine
the relationship between total protein intake and changes in
fat-free mass (FFM). Data from 49 RCT with 1863 participants showed
that dietary protein supplementation significantly (all P<0.05) increased
changes (means [95% confidence interval]) in: strength as 1RM
(2.49 kg [0.64, 4.33]), FFM (0.30 kg [0.09, 0.52]) and muscle size as
muscle fibre cross sectional area (CSA; 310 m2 [51, 570]) and midfemur
CSA (7.2 mm2 [0.20, 14.30]) during RET.
Protein supplementation
was less effective in augmenting RET-induced changes in FFM
with increasing age (-0.01 kg [-0.02, -0.00], P=0.002) and more effective
in resistance-trained individuals (0.75 kg [0.09, 1.40], P=0.03). The benefit
of protein supplementation on RET-induced changes in FFM effectively
plateaued when total protein intakes exceeded 1.62 g/kg/d.
Dietary protein supplementation is a necessary and sufficient strategy
to optimize RET-induced gains in muscle strength and hypertrophy
during prolonged RET, particularly for the elderly and those with total
daily protein intakes less than 1.6 g/kg/d.