Plant-based diets and protein supplements have grown in popularity. Questions remain regarding their efficacy for supporting muscle growth. This new meta-analysis preprint evaluates how plant and animal proteins compare in stimulating muscle protein synthesis—and whether age makes a difference.

Overview

• What did they test? The authors conducted a systematic review and Bayesian meta-analysis of 12 studies comparing the effects of plant- vs. animal-based proteins on muscle protein synthesis (MPS) in healthy adults aged 18–85 years.
• What did they find? Animal proteins showed a modest advantage in stimulating MPS overall, though the effect size was small and of low certainty. Older adults (65+) experienced greater MPS with animal proteins, while younger adults showed similar responses regardless of protein source.
• What does it mean for you? If you're younger and eating enough high-quality plant protein, you may see similar muscle-building benefits as with animal protein. Older adults, however, may benefit more from animal sources or leucine-enriched plant options to overcome anabolic resistance.

What’s the Problem?

Plant-based diets and products have been popularized in recent history. They are often embraced for ethical, environmental, and health reasons—but some concern remains regarding their ability to support muscle growth. While total daily protein intake is of critical importance, the amino acid profile of a given protein source can influence muscle protein synthesis (MPS), a key driver of muscle adaptation. Animal proteins are generally considered superior due to higher digestibility and leucine content, a branched-chain amino acid crucial for triggering MPS through mTORC1 activation 1 2. However, emerging research suggests that consuming greater quantities of plant protein, or combining plant-based sources, may offset these differences 3. Whether plant-based proteins can truly match animal sources in their anabolic potential—particularly across different age groups—remains a critical and unresolved question. Against this background, this new preprint of a meta-analysis by Mendes and colleagues is both timely and practically relevant.

Purpose

Through a systematic review and meta-analysis of the literature, the authors aimed to:

1. Compare MPS responses between plant- and animal-based proteins.
2. Examine differences by age group (18–54, 55–64, 65–85 years).
3. Explore whether resistance exercise affects differences in MPS between protein sources.

Hypothesis

No hypothesis was explicitly stated by the authors considering this was a systematic review and meta-analysis.