Does plant protein build as much muscle as animal protein?

Plant protein builds muscle. Pooled across 30 randomised trials, people eating plant protein gained slightly less muscle mass than people eating animal protein, and just as much strength [3].

The muscle gap is small and the two groups overlap heavily. It leaned the same way trial after trial rather than looking like chance, so the difference is real without being large [3]. Across the 14 trials that measured strength and the 5 that measured physical performance, nothing separated the two diets.

One earlier meta-analysis put the size in kilograms. Across 16 trials it found no overall difference in muscle or strength, and 0.41 kg more lean mass with animal protein in adults under 50 [2].

Which plant protein matters more than the plant-versus-animal split:

• Soy and milk protein finished level across 17 trials, with no difference worth the name
• Rice, chia, oat and potato protein trailed animal protein by roughly three times the overall gap, across 5 trials
• Whole plant-based diets trailed by a similar margin, across 7 trials

Age changes the answer. Under 60, animal protein kept its small edge. At 60 and over the gap essentially vanished [3].

Single meals behave differently from whole diets. In 16 healthy adults aged 65 to 85, a meal built around 100 g of lean beef raised muscle protein synthesis - the rate at which the body assembles new muscle protein in the hours after eating - about 47% more than a vegan meal matched for calories and protein [6].

The longest controlled test found no gap at all. Over 10 weeks of supervised resistance training at about 2 g of protein per kg of body weight per day, 22 young adults gained 2.6 kg of lean mass on an omnivorous diet and 3.1 kg on a non-animal, mycoprotein-rich diet - mycoprotein is protein grown from fungus and used in meat-substitute foods - with thigh muscle volume up 8.3% in both groups [16]. Habitual vegans and omnivores on protein-matched diets showed the same pattern [14].

The constraint is protein quality, not the plant or animal label. Many plant proteins are less digestible, carry fewer essential amino acids per gram, and contain less leucine, the amino acid that switches on the muscle-building pathway [1], [5], [18]. Essential amino acids are the ones the body cannot make for itself.

Some plant amino acids are taken up by the gut and liver before they ever reach muscle, a process called splanchnic extraction [1], [12].

Dose may outrank all of this. In 45 healthy men averaging 69 years old, 20 g of a soy-pea blend, the same blend fortified with 2 g of leucine, and 20 g of whey all failed to raise muscle protein synthesis above fasting levels [17]. The leucine-fortified drink pushed blood leucine higher than whey did. The muscle still did not respond.

Ageing makes this harder through anabolic resistance, a blunted muscle response to the same amount of protein [9], [12].

Most of these trials compared supplements, not dinners. Isolated soy, whey or pea powder in a shake is not a week of meals, and the pooled estimates lean heavily on that design [1], [3].

No trial in the 2025 review measured sarcopenia itself, the age-related loss of muscle and strength that the whole question is really about [3]. Everything here is a stand-in measure: kilograms of lean mass, and building rates measured over a few hours.

The evidence applies least well to:

• adults aged 60 and over, where the animal-protein advantage was too small to separate from chance [3]
• resistance-trained athletes, who are barely represented in this literature [18]
• people with obesity or metabolic disease, whose response to protein is already blunted [13]

The dose finding comes from one trial in 45 older men, all healthy, none of them women [17]. Plant proteins beyond soy, wheat, rice, chia, oat, potato and faba bean remain thinly studied [1], [3], [15].

Two lifters on 2 g of protein per kg of body weight, one omnivorous and one plant-based, would be hard to tell apart after 10 weeks on the same programme. That is roughly what the 10-week trial found: 2.6 kg and 3.1 kg of lean mass gained [16].

Two older adults eating a single 20 g serving of protein would also be hard to tell apart, for the opposite reason. Neither raised muscle protein synthesis measurably, and that included the whey [17].

The source starts to matter in between, at ordinary total protein intakes and with a plant protein that is not soy. That is where the pooled trials put animal protein ahead [3].