Plant Protein is as Good as Animal Protein for Building Muscle? New Study Breakdown! | Biolayne

Norton explains that the body's anabolic response to protein has a ceiling. When total protein intake is low, the higher leucine and essential amino acid content of animal proteins can make a measurable difference. However, once you cross roughly 1.6 g/kg, you've provided enough building blocks and leucine triggers that the source becomes less critical. This is why the new study, with participants at 1.8-1.9 g/kg, saw no difference even if the plant blend had been typical. He advises that if you struggle to hit this threshold, prioritize higher-quality proteins.

Norton points out that the study's plant blend likely had leucine matched to whey, which is not the norm. For real-world application, he suggests that vegans can still build muscle effectively by ensuring their plant protein sources collectively provide enough leucine. He mentions corn isolate as a leucine-rich option that can be added to a pea/soy blend to boost its amino acid profile. He also notes that if total protein intake is high enough, even a standard plant blend may suffice, but for those with lower intakes, strategic blending or fortification is wise.

Norton emphasizes that while protein quality can matter at the margins, the biggest variable in muscle hypertrophy is the training stimulus itself. He notes that even in studies showing small advantages for animal protein, the effect sizes are modest compared to the gains achievable through progressive overload and consistent hard training. This advice serves as a reality check for those who might over-prioritize supplementation details at the expense of training effort.

Norton references meta-analyses showing small but significant benefits of animal protein over plant protein for muscle mass and strength, particularly when total protein intake is low. He explains that this is because animal proteins are more digestible and have a better essential amino acid profile. For those who can't or won't eat large amounts of protein, selecting whey, eggs, or a leucine-fortified plant blend can help compensate.

Layne Norton breaks down the study, noting that both groups were already consuming high-protein diets (1.8-1.9 g/kg after supplementation), which saturates the muscle-building signal and minimizes quality differences. He points out that the participants were untrained young men, a population with a robust anabolic response that can wash out subtle differences. Crucially, he examined the amino acid profiles and found the pea/soy blend had slightly more leucine and essential amino acids than whey—atypical for such blends—suggesting it was fortified to match whey. The company that funded the study makes both proteins, but this specific blend is not commercially available. Norton argues the study is a proof-of-concept: if you chemically match a plant protein to an animal protein, it performs equally. He cautions against social media hot takes claiming no difference between plant and animal protein, because off-the-shelf blends have about 25% less leucine.

Norton explains that the body's muscle-building machinery has a ceiling; once you provide enough total protein and leucine, additional quality advantages are blunted. He references his own PhD research in rats, where differences between plant and animal protein were observed at a lower protein intake (15-16% of calories), but not when intake was high. This principle aligns with the new study: both groups were already at 1.8-1.9 g/kg, so any quality edge of whey was irrelevant. He emphasizes that if you're struggling to eat enough total protein, then choosing higher-quality sources (animal or fortified plant) becomes more important.

Norton describes a two-part experiment from his PhD: initially, whey elicited a much greater muscle protein synthetic response than wheat protein. In a follow-up, they fortified the wheat group with leucine to match whey's leucine content, and the difference disappeared. He then applies this to the new study, noting that the pea/soy blend had slightly more leucine than whey—highly unusual for such blends—and concludes it was likely fortified. This makes the study a proof-of-concept that chemically matching amino acid profiles equalizes anabolic response, not a test of typical plant proteins.

Norton explains that PDCAAS can overestimate plant-based proteins because it doesn't account for individual amino acid absorption at the ileum. DIAAS, in contrast, measures the digestibility of each essential amino acid at the end of the small intestine and compares it to a reference pattern. This gives whey a DIAAS of around 130, while a pea/soy blend scores about 90, reflecting real differences in amino acid bioavailability. He notes that DIAAS is becoming the accepted standard because it provides a more accurate picture of protein quality.

Norton investigated the amino acid composition of the study's blend and found it had slightly more leucine than whey, which is not characteristic of standard pea/soy products. He notes the company that funded the study manufactures both the whey and the plant blend, but the plant blend is not sold to the public. He suspects it was fortified to match whey's leucine and essential amino acid profile, making the study a proof-of-concept rather than a real-world comparison. He warns that if you buy a typical pea/soy blend, you're likely getting a lower leucine content, which might matter if your total protein intake is marginal.