The importance of leucine, one of the branched-chain amino acids, continues to emerge.
Researchers from the University of Illinois examined the impact of meals containing different amounts of leucine on the time course and magnitude of muscle protein synthesis. In the first set of experiments, it was shown that ingestion of a meal containing 20% of whey protein resulted in peak blood leucine levels after 45 minutes, and they stayed elevated for 180 minutes after ingestion. Leucine levels in the blood were correlated with the activation of key elements in muscle that stimulate protein synthesis. When leucine was highest, muscle protein synthesis peaked, and when leucine dropped to normal levels, protein synthesis decreased.
In a second series of experiments, whey protein was compared to wheat protein at varying levels of total protein intake. Regardless of background protein intake, whey protein resulted in greater increases in blood leucine and greater increases in muscle protein synthesis.
The bottom line from these experiments is that blood levels of leucine is a key factor in turning on protein synthesis. Whey protein is a high-quality source of leucine that efficiently elevates blood levels of leucine and muscle protein synthesis.