A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults

Abstract

ObjectiveWe performed a systematic review, meta-analysis and meta-regression to determine if dietary protein supplementation augments resistance exercise training (RET)-induced gains in muscle mass and strength.Data sourcesA systematic search of Medline, Embase, CINAHL and SportDiscus.Eligibility criteriaOnly randomised controlled trials with RET ≥6 weeks in duration and dietary protein supplementation.DesignRandom-effects meta-analyses and meta-regressions with four a priori determined covariates. Two-phase break point analysis was used to determine the relationship between total protein intake and changes in fat-free mass (FFM).ResultsData from 49 studies with 1863 participants showed that dietary protein supplementation significantly (all p<0.05) increased changes (means (95% CI)) in: strength—one-repetition-maximum (2.49 kg (0.64, 4.33)), FFM (0.30 kg (0.09, 0.52)) and muscle size—muscle fibre cross-sectional area (CSA; 310 µm2 (51, 570)) and mid-femur CSA (7.2 mm2 (0.20, 14.30)) during periods of prolonged RET. The impact of protein supplementation on gains in FFM was reduced with increasing age (−0.01 kg (−0.02,–0.00), p=0.002) and was more effective in resistance-trained individuals (0.75 kg (0.09, 1.40), p=0.03). Protein supplementation beyond total protein intakes of 1.62 g/kg/day resulted in no further RET-induced gains in FFM.Summary/conclusionDietary protein supplementation significantly enhanced changes in muscle strength and size during prolonged RET in healthy adults. Increasing age reduces and training experience increases the efficacy of protein supplementation during RET. With protein supplementation, protein intakes at amounts greater than ~1.6 g/kg/day do not further contribute RET-induced gains in FFM.

Benefits of higher resistance‐training volume are related to ribosome biogenesis

“…), which indeed also affects training responses (Morton et al . ). The lack of a comprehensive dietary control in the present study poses a limitation, as we cannot exclude dietary aspects from exerting confounding effects.…”

The effects of dietary protein intake on appendicular lean mass and muscle function in elderly men: a 10-wk randomized controlled trial

“…Our results suggest that appendicular lean mass loss can be caused by insufficient protein intake, yet higher protein intake does not necessarily induce muscle hypertrophy in the absence of increased physical activity. Resistance training (51) or other highintensity exercise (52) is normally required to induce muscle hypertrophy, which may be further increased with additional protein intake; this response has, however, been shown to be blunted in older adults (53).…”

AGS and NIA Bench‐to Bedside Conference Summary: Osteoporosis and Soft Tissue (Muscle and Fat) Disorders

“…Consuming more protein during caloric restriction helps older adults retain more lean mass as they lose fat mass . Protein supplementation in healthy adults also increases muscle strength and muscle mass or quality in healthy older adults and can improve functional recovery from illness . High dietary protein intakes have no adverse effects on bone health, and moderate evidence supports a protective effect on lumbar spine BMD .…”