Effects of plant- versus animal-based proteins on muscle protein synthesis: a systematic review with meta-analysis.

Abstract

Background: Plant-based proteins have gained increasing attention due to ethical, health, economic, and environmental considerations. As interest in plant-based diets grows, it is important to determine whether plant-based proteins stimulate muscle protein synthesis (MPS) as effectively as animal-based proteins, and whether these effects differ by age or post-ingestion timing.

Objective: - This systematic review with meta-analysis aimed to (1) compare the MPS response between plant- and animal-based proteins; (2) determine the differential effects of these protein sources on MPS stratified by age groups (18-54 years, 55-64 years, and 65-85 years) and post-ingestion time points (2, 4, 6, and 24 hours); and (3) explore whether resistance exercise modulates differences in MPS stimulation between protein types.

Methods: Major electronic databases (PubMed, Scopus, Cochrane, Sport Discus and Web of Science) were searched for studies comparing plant- and animal-based protein effects on MPS in healthy adults (18-85 years) up to October 2024. Risk of bias was assessed using GRADE. Meta-analyses employed Bayesian three-level hierarchical random effects models, with subgroup analyses by age, post-ingestion time, and resistance exercise.

Results: Twelve studies met inclusion criteria. Overall, results slightly favored animal-based proteins (ES_Plant:Animal = 0.004 [95%CrI: -0.002 to 0.011]), although differences were small and within typical fasted-state MPS rates, with substantial uncertainty. Most animal protein data were derived from milk-based sources, while plant proteins were heterogeneous; therefore, generalization to all protein sources should be made with caution. Adults aged ≥65 years showed a modest advantage for animal proteins (ES = 0.013 [95% CrI: 0.000 to 0.027]), whereas younger adults exhibited similar MPS responses between protein sources. No substantial differences were observed across post-ingestion time points or resistance exercise conditions, although data were limited.

Conclusions: Although point estimates tended to favor animal-based proteins, particularly in older adults, the relatively small number of studies and imprecision of the pooled estimates limit the strength of conclusions. Further high-quality trials are needed to determine if plant-based proteins can match the anabolic potential of animal-based proteins.