Effects of Plant-Based Protein Interventions, with and without an Exercise Component, on Body Composition, Strength and Physical Function in Older Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Abstract

Maintaining muscle mass, strength, and function is crucial for our aging population. Exercise and dietary protein intake are recommended strategies; however, animal proteins have been the most studied. Plant-based protein sources have lower digestibility and incomplete amino acid profiles. However new innovative plant-based proteins and products may have overcome these issues. Therefore, this systematic review aimed to synthesize the current research and evaluate the effects of plant-based protein interventions compared to placebo on body composition, strength, and physical function in older adults (≥60 years old). The secondary aim was whether exercise improved the effectiveness of plant-based protein on these outcomes. Randomized controlled trials up to January 2023 were identified through Medline, EMBASE, CINAHL, and Cochrane Library databases. Studies contained a plant-protein intervention, and assessed body composition, strength, and/or physical function. Thirteen articles were included, all using soy protein (0.6-60 g daily), from 12 weeks to 1 year. Narrative summary reported positive effects on muscle mass over time, with no significant differences compared to controls (no intervention, exercise only, animal protein, or exercise + animal protein interventions). There was limited impact on strength and function. Meta-analysis showed that plant-protein interventions were comparable to controls, in all outcomes. In conclusion, plant-protein interventions improved muscle mass over time, and were comparable to other interventions, warranting further investigation as an anabolic stimulus in this vulnerable population.

Keywords: animal protein; body composition; exercise; muscle mass; older adults; physical function; plant protein; strength.

Figure 1

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram.

Figure 2

Forest plot of randomized controlled studies examining the effect of plant protein interventions on fat mass. Individual study effect estimates (green boxes) and the pooled effect estimate (diamond) are shown. Values are standardized mean differences with 95% confidence intervals (CI) determined using generic inverse-variance random-effects models. Heterogeneity was quantified by I² at a significance of p < 0.10 [47,49,53,54,56].

Figure 3

Forest plot of randomized controlled studies examining the effect of plant protein interventions on lean muscle mass. Individual study effect estimates (green boxes) and the pooled effect estimate (diamond) are shown. Values are standardized mean differences with 95% confidence intervals (CI) determined using generic inverse-variance random-effects models. Heterogeneity was quantified by I² at a significance of p < 0.10 [47,49,50,51,52,53,54,55,56].

Figure 4

Forest plot of randomized controlled studies examining the effect of plant protein interventions on knee extension strength. Individual study effect estimates (green boxes) and the pooled effect estimate (diamond) are shown. Values are standardized mean differences with 95% confidence intervals (CI) determined using generic inverse-variance random-effects models. Heterogeneity was quantified by I² at a significance of p < 0.10 [47,49,52,56].

Figure 5

Forest plot of randomized controlled studies examining the effect of plant protein interventions on gait speed. Individual study effect estimates (green boxes) and the pooled effect estimate (diamond) are shown. Values are standardized mean differences with 95% confidence intervals (CI) determined using generic inverse-variance random-effects models. Heterogeneity was quantified by I² at a significance of p < 0.10 [50,51,55].

Figure 6

Forest plot of randomized controlled studies examining the effect of plant protein interventions on lean muscle mass, sub-grouped by exercise component. Individual study effect estimates (green boxes) and the pooled effect estimate (diamond) are shown. Values are standardized mean differences with 95% confidence intervals (CI) determined using generic inverse-variance random-effects models. Heterogeneity was quantified by I² at a significance of p < 0.10 [47,49,50,51,52,53,54,55,56].

Figure 7

Forest plot of randomized controlled studies examining the effect of plant protein interventions on lean muscle mass, sub-grouped by protein comparison component. Individual study effect estimates (green boxes) and the pooled effect estimate (diamond) are shown. Values are standardized mean differences with 95% confidence intervals (CI) determined using generic inverse-variance random-effects models. Heterogeneity was quantified by I² at a significance of p < 0.10 [47,49,50,51,52,53,54,55,56].