Richard P Kirwan1, Mohsen Mazidi2,3, Carmen Rodríguez García4, Katie E Lane5, Alireza Jafari6, Tom Butler7, Fatima Perez de Heredia1, Ian G Davies5. 1. School of Biological and Environmental Sciences, Liverpool John Moores University, Liverpool, UK. 2. Department of Twin Research and Genetic Epidemiology, King's College London, London, UK. 3. Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK. 4. Department of Health Sciences, Faculty of Experimental Sciences, University of Jaén, Jaén, Spain. 5. Research Institute of Sport and Exercise Science, Liverpool John Moores University, Liverpool, UK. 6. Department of Community Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences, Tehran, Iran. 7. School of Applied Health and Social Care and Social Work, Faculty of Health, Social Care and Medicine, Edge Hill University, Ormskirk, UK.
Abstract
BACKGROUND: Increased protein intake is suggested as a strategy to slow or reverse the loss of muscle mass and strength observed in sarcopenia, but results from studies that directly tested this possibility have been inconsistent. OBJECTIVES: We assessed the evidence on the effects of whole protein supplementation or higher-protein diets, without the use of amino acids or supplements known to stimulate hypertrophy, alone or in combination with resistance exercise (RE) interventions, on lean body mass (LBM) and strength in older adults. METHODS: A systematic search was conducted using PubMed, Medline, Web of Science, and Cochrane CENTRAL databases from January 1990 to July 2021. Randomized controlled trials that assessed the effects of protein supplementation and/or higher-protein dietary interventions in older adults (mean age ≥50 y) on total LBM, appendicular lean mass (ALM), and handgrip (HG) and knee extension (KE) strength were included. RESULTS: Twenty-eight studies were identified. In pooled analysis, compared with lower protein controls, protein supplementation did not have a significant positive effect on total LBM [weighted mean difference in change (WMD): 0.34; 95% CI: -0.21, 0.89; I2 = 90.01%], ALM (WMD: 0.4; 95% CI: -0.01, 0.81; I2 = 90.38%), HG strength (WMD: 0.69; 95% CI: -0.69, 2.06; I2 = 94.52%), or KE strength (WMD: 1.88; 95% CI: -0.6, 4.35; I2 = 95.35%). However, in interventions that used also RE, statistically significant positive effects of protein were observed for ALM (WMD: 0.54; 95% CI: 0.03, 1.05; I2 = 89.76%) and HG (WMD: 1.71; 95% CI: 0.12, 3.30; I2 = 88.71%). Meta-regression revealed no significant association between age, per-meal protein dose, duration, and baseline protein intake with change in any outcome. Subgroup analysis revealed the statistically significant effects on ALM occurred only in sarcopenic/frail populations (WMD: 0.88; 95% CI: 0.51, 1.25; I2 = 79.0%). Most studies (n = 22) had some risk of bias. CONCLUSIONS: In older adults performing RE, increased protein intake leads to greater ALM and HG strength compared with lower protein controls. Without RE, protein has no additional benefit on changes in total LBM, ALM, or HG strength.
BACKGROUND: Increased protein intake is suggested as a strategy to slow or reverse the loss of muscle mass and strength observed in sarcopenia, but results from studies that directly tested this possibility have been inconsistent. OBJECTIVES: We assessed the evidence on the effects of whole protein supplementation or higher-protein diets, without the use of amino acids or supplements known to stimulate hypertrophy, alone or in combination with resistance exercise (RE) interventions, on lean body mass (LBM) and strength in older adults. METHODS: A systematic search was conducted using PubMed, Medline, Web of Science, and Cochrane CENTRAL databases from January 1990 to July 2021. Randomized controlled trials that assessed the effects of protein supplementation and/or higher-protein dietary interventions in older adults (mean age ≥50 y) on total LBM, appendicular lean mass (ALM), and handgrip (HG) and knee extension (KE) strength were included. RESULTS: Twenty-eight studies were identified. In pooled analysis, compared with lower protein controls, protein supplementation did not have a significant positive effect on total LBM [weighted mean difference in change (WMD): 0.34; 95% CI: -0.21, 0.89; I2 = 90.01%], ALM (WMD: 0.4; 95% CI: -0.01, 0.81; I2 = 90.38%), HG strength (WMD: 0.69; 95% CI: -0.69, 2.06; I2 = 94.52%), or KE strength (WMD: 1.88; 95% CI: -0.6, 4.35; I2 = 95.35%). However, in interventions that used also RE, statistically significant positive effects of protein were observed for ALM (WMD: 0.54; 95% CI: 0.03, 1.05; I2 = 89.76%) and HG (WMD: 1.71; 95% CI: 0.12, 3.30; I2 = 88.71%). Meta-regression revealed no significant association between age, per-meal protein dose, duration, and baseline protein intake with change in any outcome. Subgroup analysis revealed the statistically significant effects on ALM occurred only in sarcopenic/frail populations (WMD: 0.88; 95% CI: 0.51, 1.25; I2 = 79.0%). Most studies (n = 22) had some risk of bias. CONCLUSIONS: In older adults performing RE, increased protein intake leads to greater ALM and HG strength compared with lower protein controls. Without RE, protein has no additional benefit on changes in total LBM, ALM, or HG strength.
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