Leucine is the primary driver of muscle hypertrophy; for proteins (particularly plant-based ones) to be effective, they must contain a sufficient quantity of this amino acid.

noli's read

Professor Stuart Phillips relies on a solid understanding of muscle protein synthesis, where leucine acts as a metabolic trigger (a 'switch') for growth. Research, including meta-analyses and randomized controlled trials (RCTs) on protein quality, confirms that leucine activates the mTOR pathway, which is essential for muscle development. It is accurate that certain plant-based sources are naturally less dense in leucine or exhibit lower digestibility, which can dampen the anabolic response compared to animal proteins. However, the advice is nuanced: it does not state that plant-based proteins are ineffective, but highlights that they require specific attention to dose or blending to reach the critical leucine threshold. The concept that leucine is the key mediator is supported by current scientific literature. The assertion is therefore scientifically coherent and avoids the pitfall of oversimplification by focusing on the physiological mechanism rather than the protein source itself.

the sources

No named source held this one up — that absence is part of the verdict.