Is plant protein as good as animal protein (or whey) for building muscle?

The picture is more mixed than it is often made out to be. A systematic review with meta-analysis by Lim and colleagues pooled 16 controlled trials and found no difference in muscle strength between animal and plant protein. But among adults under 50, animal protein came out ahead on both measures of lean mass: absolute lean mass increased 0.41 kg more (95% CI 0.08 to 0.74) and percent lean mass 0.50 percentage points more (95% CI 0.00 to 1.01), both statistically significant. The authors themselves summarise the finding this way: animal protein tends to be more beneficial for lean mass than plant protein, especially in younger adults.

Two intervention studies with carefully matched protein intake add nuance to that picture. Hevia-Larraín and colleagues had habitual vegans and omnivores strength-train on 1.6 grams of protein per kilo of body weight a day. Both groups built the same amount of leg muscle, about 1.2 kilos each, and gained strength equally. Monteyne and colleagues randomised young adults to a vegan or a mixed diet at 1.8 to 2 grams per kilo and measured protein synthesis directly. Muscle growth was equivalent, with thigh volume rising 8.3 percent in both groups.

The difference between these studies likely comes down to exactly this: how carefully protein intake is matched and how varied the sources are. Plant protein tends to be slightly lower in the amino acid leucine and is digested a little less efficiently, so a single plant source can be at a slight disadvantage next to whey or eggs, especially at a lower total intake or in younger people with greater muscle-protein demand. When the day's protein is sufficient, matched, and the sources vary, as in the Hevia-Larraín and Monteyne trials, the gap closes. Legumes, soy, grains and nuts together cover the full amino acid requirement.

The myth survives on the word complete. School biology and older nutrition taught protein as complete or incomplete, a split built on experiments with single proteins in isolation rather than on what a full day of food looks like. Combine different plant sources and every amino acid is still covered. Then come the incentives. Whey and animal protein powders are a large market, and the marketing leans on the idea of high-quality protein. Gym culture has long equated meat, eggs and whey with muscle, while beans and lentils were cast as second-class protein. The image lingers even though modern research has evened it out.

Focus on total amount before source. Get enough protein across the day and you build muscle just as well on a plant-based diet. If you want to eat mostly plants, vary the sources: legumes, soy, tofu, grains and nuts complement each other. Aim a little higher if you train hard, since plant protein digests slightly less efficiently. Work out your own protein target with the calculator, so the amount becomes concrete rather than a guess.