Systematic review and meta‐analysis of protein intake to support muscle mass and function in healthy adults

Abstract

We performed a systematic review, meta‐analysis, and meta‐regression to determine if increasing daily protein ingestion contributes to gaining lean body mass (LBM), muscle strength, and physical/functional test performance in healthy subjects. A protocol for the present study was registered (PROSPERO, CRD42020159001), and a systematic search of Medline, Embase, CINAHL, and Web of Sciences databases was undertaken. Only randomized controlled trials (RCT) where participants increased their daily protein intake and were healthy and non‐obese adults were included. Research questions focused on the main effects on the outcomes of interest and subgroup analysis, splitting the studies by participation in a resistance exercise (RE), age (<65 or ≥65 years old), and levels of daily protein ingestion. Three‐level random‐effects meta‐analyses and meta‐regressions were conducted on data from 74 RCT. Most of the selected studies tested the effects of additional protein ingestion during RE training. The evidence suggests that increasing daily protein ingestion may enhance gains in LBM in studies enrolling subjects in RE (SMD [standardized mean difference] = 0.22, 95% CI [95% confidence interval] 0.14:0.30, P < 0.01, 62 studies, moderate level of evidence). The effect on LBM was significant in subjects ≥65 years old ingesting 1.2–1.59 g of protein/kg/day and for younger subjects (<65 years old) ingesting ≥1.6 g of protein/kg/day submitted to RE. Lower‐body strength gain was slightly higher by additional protein ingestion at ≥1.6 g of protein/kg/day during RE training (SMD = 0.40, 95% CI 0.09:0.35, P < 0.01, 19 studies, low level of evidence). Bench press strength is slightly increased by ingesting more protein in <65 years old subjects during RE training (SMD = 0.18, 95% CI 0.03:0.33, P = 0.01, 32 studies, low level of evidence). The effects of ingesting more protein are unclear when assessing handgrip strength and only marginal for performance in physical function tests. In conclusion, increasing daily protein ingestion results in small additional gains in LBM and lower body muscle strength gains in healthy adults enrolled in resistance exercise training. There is a slight effect on bench press strength and minimal effect performance in physical function tests. The effect on handgrip strength is unclear.

Synergistic Effect of Increased Total Protein Intake and Strength Training on Muscle Strength: A Dose-Response Meta-analysis of Randomized Controlled Trials

“…The spline model results showed that muscle strength with resistance training increased proportionally at the rate of 0.72% (95% CI 0.40–1.04%) per 0.1 g/kg BW/d increase in total protein intake up to 1.5 g/kg BW/d, but no further gains are achieved thereafter. This result resembles that of a previous meta-analysis [ 39 ] to some degree, in which the effects of total protein intake on bench press strength were not different between below and above 1.6 g/kg BW/d. However, further researches are needed to better understand the mechanism regulating the effectiveness of total protein intake at 1.5 g/kg BW/d for muscle strength.…”

“…Second, the spline model results showed that 1.5 g/kg BW/d total protein intake with resistance training is required to achieve the optimal effect on muscle strength. To the best of our knowledge, while a few studies have investigated the dose-response relationship of total protein intake to muscle mass [ 32 , 38 , 39 ] or strength [ 39 ], this study is the first meta-analysis to quantitatively assess the detailed dose-response relationship between total protein intake and muscle strength in both training and non-training study participants.…”

“…Supplemental protein intake (g/d or g/kg body weight [BW]/d) was the value determined before the intervention. Trials with muscular hypertrophic agents (e.g., leucine, β-hydroxy-β-methyl butyrate, creatine or vitamin D), energy restriction or overfeeding were excluded, after consulting previous meta-analyses [ 31 , 32 , 34 , 35 , 39 ]. For trials with two or more control groups, the group with the same energy intake and larger gap in the supplemented protein intake was included as a control in the analysis.…”

“…However, there is no general consensus on whether supplemental protein intake would lead to muscle strength increase in people who do not perform resistance training [ 31 – 37 ]. Furthermore, although there are a few studies regarding the dose-response relationship of total protein intake to muscle mass [ 32 , 38 , 39 ] or strength [ 39 ], the detailed dose-response relationship between total protein intake and muscle strength increase is yet to be clarified, especially in the absence of resistance training. This study aimed to clarify the detailed dose-response relationship between protein supplementation and muscle strength with and without resistance training.…”

Effects of a New Multicomponent Nutritional Supplement on Muscle Mass and Physical Performance in Adult and Old Patients Recovered from COVID-19: A Pilot Observational Case–Control Study

“…International guidelines and expert consensus recommend appropriate and timely nutritional evaluation and specific approaches to improve clinical outcomes in subjects at higher risk of developing nutritional problems, including subjects with chronic and/or severe diseases in different healthcare settings [ 6 , 15 , 16 ]. The present study suggests and confirms the importance of nutritional supplementation in subjects suffering from an infection and catabolic disease, such as COVID-19.…”