When it comes to stimulating muscle protein synthesis, Leucine is the key. Studies have shown that a certain amount of Leucine must be inside muscle cells to trigger maximal muscle protein synthesis; this is called the Leucine ‘threshold’.
Protein sources vary in their Leucine content and digestibility, so it would seem that sources rich in Leucine that are easily digested and absorbed by our bodies would be the best for maximizing protein synthesis after exercise.
Stuart M. Phillips, PhD, Professor at McMaster University and Director of the McMaster Centre for Nutrition, Exercise, and Health Research, found evidence to support this idea in his peer-reviewed paper titled “The impact of protein quality on the promotion of resistance exercise-induced changes in muscle mass” published in the journal Nutrition & Metabolism this month.
This means that proteins like whey, which are rich in Leucine and highly digestible, are inherently great for stimulating muscle protein synthesis, while plant proteins may need to be optimized via blending or processing to improve amino acid content and digestibility to achieve the same result.