Animal Protein vs Plant Protein for Muscle and Strength
But there is a catch.
A major systematic review and meta-analysis published in Nutrition Reviews examined whether the source of your protein matters when building muscle. Researchers pooled data from 43 randomised controlled trials (30 with enough data for statistical analysis) involving 1,538 participants to compare how plant and animal proteins affect muscle mass, strength, and physical performance. The finding: animal protein delivered a small but meaningful advantage over most plant proteins for muscle mass, particularly in younger adults and when combined with resistance training. However, soy protein performed equally as well as milk protein across all age groups. The research also revealed that whole food plant-based diets showed inferior results compared to omnivorous diets when protein content was matched. The study, conducted by researchers at Queen’s University Belfast, represents the first comprehensive comparison of diverse plant proteins (not just soy) against animal sources using rigorous meta-analysis methods.
Methods
The research team searched five major databases—Medline, Embase, Scopus, Web of Science, and Cochrane Central—pulling studies published through June 2023. They included only randomised controlled trials lasting at least 4 weeks. To make fair comparisons, plant and animal protein amounts had to be nearly identical (within 5 grams for supplements or a matching percentage of daily calories for whole-diet studies). Studies were excluded if participants had medical conditions affecting protein absorption or metabolism, such as cancer, kidney disease, or severe malnutrition. Thirty trials measuring muscle mass met criteria for meta-analysis. The researchers used standardised statistical techniques to combine results and assessed study quality using the Cochrane Risk of Bias 2.0 tool, considered the gold standard for RCT evaluation. They also examined whether results differed based on age (under 60 vs. 60 and older), sex, exercise involvement, and specific protein sources.
Results
Overall Muscle Mass: Animal protein produced slightly better results than plant protein for muscle mass gains. The advantage was stronger in younger adults under 60 than in those 60 and older, where the difference nearly disappeared. When resistance training was included alongside protein, animal protein showed a more pronounced benefit compared to plant protein.
Soy Protein Performs Equally: Here’s the critical distinction. When researchers specifically compared soy protein against milk protein using 17 trials, no meaningful difference emerged. Soy matched milk protein for muscle mass improvements in both younger and older participants and across both sexes. This held true whether looking at isolated soy supplements or whole soy foods.
Non-Soy Plant Proteins Fall Short: Rice, pea, oat, potato, and chia seed proteins showed inferior results compared to animal protein in five combined trials. Animal protein produced notably better muscle mass outcomes than these alternatives. However, the researchers noted this conclusion is tentative because the number of studies examining these specific plant sources remains limited.
Plant-Based Diets Show Larger Gaps: When examining whole dietary patterns (seven trials, 327 participants), plant-based and vegan diets resulted in less muscle mass compared to omnivorous diets with matched protein content. The researchers attribute this to structural differences in plant proteins. Plant proteins have secondary structures that make them harder to digest, and plant foods contain antinutrients like lectins and protease inhibitors that further reduce protein absorption in the gut. Highly processed soy isolates and concentrates overcome these barriers better than whole plant foods.
Strength and Performance: There were no significant differences between plant and animal protein for muscle strength or physical performance across the trials examined. This suggests protein source matters less for functional outcomes than for muscle mass specifically.
Training Effect: All 16 trials combining protein with resistance training showed significant muscle improvements, while only 21% of studies without training reported meaningful changes. Across trials, animal protein combined with resistance training proved more effective for muscle mass than plant protein plus training.
Takeaways
If building muscle is your priority, here’s what the evidence shows: animal and soy proteins work equally well for promoting muscle mass regardless of age. If you’re consuming other plant proteins (rice, pea, oat, chia, or potato), you’ll likely see less impressive gains compared to animal sources, particularly in younger lifters. The advantage of animal protein over non-soy plant options was small, not dramatic, but it was consistent across multiple studies.
The finding about whole plant-based diets is crucial: if you’re eating a vegan or heavily plant-based diet, the surrounding foods matter. Antinutrients and structural differences in plant proteins reduce bioavailability. This can be partially offset by cooking methods like boiling, pressure cooking, or microwaving that reduce protease inhibitors, or by choosing heavily processed plant protein isolates and concentrates over whole foods.
Resistance training emerged as essential regardless of protein source. None of the dietary protein advantages showed up in studies lacking structured resistance work. Combining adequate protein with consistent lifting produces better results than protein alone.
Older adults (60-plus) showed minimal differences between animal and plant proteins, suggesting age-related changes in muscle responsiveness may partially explain why younger lifters saw larger gaps between protein sources.
For sarcopenia prevention and treatment in older populations, the evidence base remains thin. No trials specifically examined sarcopenia as an outcome, so recommendations for this vulnerable group require cautious interpretation.
Reference
Reid-McCann, R. J., Brennan, S. F., Ward, N. A., Logan, D., McKinley, M. C., & McEvoy, C. T. (2025). Effect of Plant Versus Animal Protein on Muscle Mass, Strength, Physical Performance, and Sarcopenia: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Nutrition Reviews, 83(7), e1581-e1603. https://doi.org/10.1093/nutrit/nuae200
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