Egg White Protein Promotes Developmental Growth in Rodent Muscle Independent of the Leucine Content.

Leucine has been shown to have unique anabolic properties as a nutrient signal that stimulates muscle protein synthesis. Therefore, we hypothesized that the growth-promoting effect of dietary protein is dependent on the leucine concentrations. To test this hypothesis, we selected three dietary proteins: casein (CAS), egg white protein (EWP), and albumin (ALB) representing the leucine concentrations of approximately 8.3, 7.7, and 6.7% of protein (w/w), respectively. These proteins were chronically fed to growing rats as a protein source of diet for 14-day. As result, the muscle growth was the highest when the rats were fed the EWP diet, followed, in order, by the ALB and CAS diets. Thus, leucine may not be the only factor determining protein quality for muscle development. Meanwhile, the changes in muscle arginine concentration following acute EWP, ALB, and CAS administration paralleled those of muscle growth. Moreover, chronic supplementation of arginine to the CAS diet partly mimicked the EWP-induced muscle growth effect, indicating that arginine derived from EWP plays a significant role in the promotion of muscle anabolism. Translation of these results may allow for improved muscle growth in mammals fed EWP as a dietary protein source.