Effects of Plant- vs Animal-Based Proteins on Muscle Protein Synthesis: A Systematic Review With Meta-Analysis

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 postingestion timing.

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

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 to 85 years) up to October 2024. Risk of bias was assessed using the Grading of Recommendations Assessment, Development, and Evaluation system. Meta-analyses employed Bayesian 3-level hierarchical random effects models, with subgroup analyses by age, postingestion time, and resistance exercise.

Twelve studies met the inclusion criteria. Overall, results slightly favored animal-based proteins (effect size [ES]_Plant:Animal = 0.004, 95% credible interval [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, whereas plant proteins were heterogeneous; therefore, generalization to all protein sources should be made with caution. Adults aged 65 years and older showed a modest advantage for animal proteins (ES = 0.013, 95% credible interval 0.000 to 0.027), whereas younger adults exhibited similar MPS responses between protein sources. No substantial differences were observed across postingestion time points or resistance exercise conditions, although data were limited.

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.