Plant protein matches animal protein for strength gains

Animal protein is widely assumed to beat plant protein for building muscle, largely because it stimulates muscle protein synthesis more strongly in acute lab studies. But an acute advantage in a lab measure does not automatically translate into more muscle or strength over weeks and months of real eating and training. With more people shifting towards plant-based diets, the practical question is whether protein source actually changes the outcomes that matter. This review set out to test that directly, and to ask whether resistance training or age alters the answer.

The authors searched four databases and screened 3081 articles, selecting 18 for systematic review and 16 for meta-analysis. Included studies were randomised controlled trials comparing animal protein with plant protein and measuring lean mass or muscle strength. Total protein intakes were generally above the recommended dietary allowance at both baseline and the end of the interventions. Analyses examined absolute lean mass, percent lean mass and strength, with subgroups for resistance training and for age above or below 50.

Protein source made no difference to changes in absolute lean mass or muscle strength overall. Animal protein did show a favouring effect on percent lean mass. Whether participants were also doing resistance training had no influence on the results. In adults under 50, animal protein produced greater gains in absolute lean mass, a weighted mean difference of 0.41 kg, and in percent lean mass of 0.50%.

The result softens a common assumption: the acute muscle protein synthesis advantage of animal protein did not translate into greater strength or absolute lean mass in these trials. A modest edge survived only on percent lean mass and among younger adults. Notably, intakes were already above the recommended allowance, so the comparison says little about lower protein diets, where source quality might matter more. Longer trials in older adults and in well-trained lifters remain open territory.

If your total protein intake is adequate, this is a reason to think the animal versus plant question matters less than the internet suggests. Strength gains did not differ by source, and neither did absolute lean mass overall. Adults under 50 chasing every kilogram of lean tissue saw a small advantage from animal protein, sized at 0.41 kg across the trials. For everyone else, hitting the total looks like the main event.