Effect of Plant Versus Animal Protein on Muscle Mass, Strength, Physical Performance, and Sarcopenia: A Systematic Review and Meta-analysis of Randomized Controlled Trials

Abstract

Context: Dietary protein is recommended for sarcopenia-a debilitating condition of age-related loss of muscle mass and strength that affects 27% of older adults. The effects of protein on muscle health may depend on protein quality.

Objective: The aim was to synthesize randomized controlled trial (RCT) data comparing plant with animal protein for muscle health.

Data sources: Forty-three eligible RCTs were sourced from Medline, Embase, Scopus, Web of Science, and CENTRAL databases.

Data extraction: Four reviewers (R.J.R.-M., S.F.B., N.A.W., D.L.) extracted data from RCTs (study setting, population, intervention characteristics, outcomes, summary statistics) and conducted quality assessment using the Cochrane Risk of Bias 2.0.

Data analysis: Standardized mean differences (SMDs) (95% CIs) were combined using a random-effects meta-analysis and forest plots were generated. I2 statistics were calculated to test for statistical heterogeneity.

Conclusion: Thirty RCTs (70%) were eligible for meta-analysis and all examined muscle mass outcomes. Compared with animal protein, plant protein resulted in lower muscle mass following the intervention (SMD = -0.20; 95% CI: -0.37, -0.03; P = .02), with stronger effects in younger (<60 years; SMD = -0.20; 95% CI: -0.37, -0.03; P = .02) than in older (≥60 years; SMD = -0.05; 95% CI: -0.32, 0.23; P = .74) adults. There was no pooled effect difference between soy and milk protein for muscle mass (SMD = -0.02; 95% CI: -0.20, 0.16; P = .80) (n = 17 RCTs), yet animal protein improved muscle mass compared with non-soy plant proteins (rice, chia, oat, and potato; SMD = -0.58; 95% CI: -1.06, -0.09; P = .02) (n = 5 RCTs) and plant-based diets (SMD = -0.51; 95% CI: -0.91, -0.11; P = .01) (n = 7 RCTs). No significant difference was found between plant or animal protein for muscle strength (n = 14 RCTs) or physical performance (n = 5 RCTs). No trials examined sarcopenia as an outcome. Animal protein may have a small beneficial effect over non-soy plant protein for muscle mass; however, research into a wider range of plant proteins and diets is needed.

Systematic review registration: PROSPERO registration no. CRD42020188658.

Keywords: dietary protein; meta-analysis; muscle mass; physical performance; sarcopenia; strength.

Figure 1.

PRISMA © Flow Diagram Displaying the Number of Studies Retrieved, Screened, Assessed for Eligibility, and Excluded at Full-Text Review Stage, Including Reasons for Exclusion. Abbreviation: PRISMA, Preferred Reporting Items for Systematic Review and Meta-Analyses

Figure 2.

Quality Assessment of 43 Included Trials Using Cochrane Risk of Bias 2.0 (RoB2)

Figure 3.

Meta-analysis of Change in Absolute Muscle Mass in Response to Plant vs Animal Protein Intervention, Overall and in Younger (<60 y) and Older (≥60 y) Adults. *Evans et al (i) denotes the groups who received the protein intervention alone and (ii) denotes those who received protein and exercise interventions. ^†Gonzáles-Salazar et al (i) denotes the groups who received a normal protein diet (19% of daily energy) and (ii) denotes those who received a high protein diet (29% of daily energy). Abbreviations: IV, inverse variance; Std, standardized

Figure 4.

Subgroup Analysis of Change in Absolute Muscle Mass in Response to Plant vs Animal Protein Interventions, Grouped by Plant Protein Source. One trial was excluded from subgroup analysis because the plant protein supplement was a combination of soy and non-soy proteins. *Evans et al (i) denotes the groups who received the protein intervention alone and (ii) denotes those who received protein and exercise interventions. ^†Gonzáles-Salazar et al (i) denotes the groups who received a normal protein diet (19% of daily energy) and (ii) denotes those who received a high protein diet (29% of daily energy). Abbreviations: IV, inverse variance; Std, standardized

Figure 5.

Meta-analysis of Change in Lower Body Strength in Response to Plant vs Animal Protein Interventions, Overall and in Younger (<60 y) and Older (≥60 y) Adults. Abbreviations: IV, inverse variance; Std, standardized