Effect of Protein or Essential Amino Acid Supplementation During Prolonged Resistance Exercise Training in Older Adults on Body Composition, Muscle Strength, and Physical Performance Parameters: A Systematic Review

Objectives: Loss of muscle mass and strength with aging, sarcopenia, burdens many older adults, making identification of strategies on how to counteract it very relevant—especially to health care providers working in rehabilitation. The aim of this systematic review was to determine the effect of protein or essential amino acid (EAA) supplementation during prolonged resistance exercise training (RT) in older adults. No known stimulants of muscle protein synthesis, or ingredients with an effect on muscle strength/physical function, were allowed with the supplementation, differentiating this systematic review from others. Data sources and methods: In January 2017, 4 electronic databases and reference lists were searched for randomized controlled trials investigating the effect of protein or EAA supplementation during RT in older adults (mean age >60 years) on outcomes of body composition, muscle strength, and physical performance. Study selection and data extraction were performed by 2 independent reviewers. Results Sixteen studies (1107 participants) fulfilled the eligibility criteria. Methodologic differences between the studies disallowed a meta-analysis. Of the 16 studies, 6 found significant effects on body composition (3 studies), muscle strength (3 studies), and physical performance (2 studies) measures. Conclusions The evidence is weak and inconsistent, as benefit of protein or EAA supplementation during RT in older adults is only shown in some studies. The findings indicate that frail/sarcopenic older adults might benefit more than healthy older adults. Further research is needed to allow an interpretation on the importance of study population and design. Trial registration: PROSPERO, Reg. no.: CRD42017063808. Registered April 14, 2017.