Protein interventions augment the effect of resistance exercise on appendicular lean mass and handgrip strength in older adults: a systematic review and meta-analysis of randomized controlled trials

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. Design A systematic search was conducted using PubMed, Medline, Web of Science and Cochrane CENTRAL databases from January 1990 up 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 years), on total LBM, appendicular lean mass (ALM), handgrip (HG) and knee extension strength (KE) were included. Results 28 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 [WMD:0.69, 95% CI: –0.69,2.06, I2:94.52%] or KE [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. Sub-group analysis revealed the statistically significant effects on ALM only occurred 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, compared with lower protein controls. Without RE, protein has no additional benefit on changes in total LBM, ALM or HG.

Mapping ongoing nutrition intervention trials in muscle, sarcopenia, and cachexia: a scoping review of future research

“…We found a wide range of dosage regimens under investigation in these trials, and only a few of them compare different protein doses within the same study. Moreover, controversies exist regarding whether larger protein doses (30 to 40 g) per meal should be recommended to optimize muscle anabolism 33,59 . Testing the impact of different protein doses (per day and meal) and distinct amino acid composition (e.g.…”

“…Despite the diversity of intervention approaches, our results indicate that food supplements and ONS composed of protein, amino acids, HMB, or omega‐3 fatty acids are of particular interest by researchers in the field given their potential for anabolic effects. 53 , 54 Although these are not novel nutrition interventions, as highlighted by a number of systematic reviews, 22 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 further research is needed to understand their impact on muscle mass and function.…”

“…Moreover, controversies exist regarding whether larger protein doses (30 to 40 g) per meal should be recommended to optimize muscle anabolism. 33 , 59 Testing the impact of different protein doses (per day and meal) and distinct amino acid composition (e.g. high in essential amino acids) on muscle‐related outcomes is therefore recommended in future studies, as protein bioavailability is determined by many factors 11 , 60 , 61 , 62 and ongoing trials are not sufficiently addressing these questions.…”

“… 22 , 28 , 29 , 30 , 31 , 32 Furthermore, the number of studies is relatively small (particularly in clinical populations), often lack measures of dietary intake and adherence and are limited by the methodological challenges to assess muscle parameters. 25 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 …”

Healthy U.S.-style dietary patterns can be modified to provide increased energy from protein

“…For example, compared with a balanced diet proving 17% energy as protein and 33% energy as fat (12% energy as saturated fat), a diet providing 27% energy as protein and 28% energy as fat (6% energy as saturated fat) with 153 g lean beef daily for five weeks resulted in lower total cholesterol and LDL-cholesterol and lower systolic blood pressure in a sample of adults with hypercholesterolemia [ 12 , 13 ]. Dietary patterns providing a higher percentage of energy from protein while remaining within the AMDR (i.e., no more than 35% energy from protein) may have beneficial effects including improved body weight management in adults with overweight or obesity [ 14 ], or lean mass and handgrip strength in the elderly when combined with resistance exercise [ 15 ]. Findings from a 2021 meta-analysis of 54 randomized controlled trials show that compared to diets providing on average 18% energy from protein (range of 10–23%), higher protein diets (average of 28% energy from protein, range of 20–45%) can support weight loss and reductions in fat mass, and lower systolic blood pressure, total cholesterol, triacylglycerol, and fasting insulin without adverse effects on other cardiometabolic risk factors [ 16 ].…”