The impact of protein quality on the promotion of resistance exercise-induced changes in muscle mass


The effects of dietary protein and amino acids on skeletal metabolism.

Study summary:

  • Isoleucine and leucine cause a reduction in serum levels of Insulin-like growth factor 1 (IGF-1)
  • Phenylalanine and histidine cause a rise in serum levels of IGF-1
  • Milk contains more phenylalanine and less isoleucin than meat products
  • Arginine & lysine intake and calcium absorption rate are positively correlated in a low protein diet
  • Similarly, phenylalanine and histidine reduce bone loss in a low protein diet, mainly through stimulation of osteoblasts

Important quotes:

  • ‘There is some evidence to suggest that arginine enhances the action of growth hormone releasing hormone, thereby increasing the secretion of growth hormone from the anterior pituitary (Ghigo et al., 2001). These data would suggest that dietary supplementation with arginine should increase circulating levels of IGF-1.’
  • ‘Supplementation with the branched chain amino acids, isoleucine and leucine, caused a reduction in serum levels of [Insulin-like growth factor-binding protein 2 (IGFBP-2)], while the aromatic amino acids, phenylalanine and histidine, increased IGF-1 levels. Milk contains greater amounts of phenylalanine and lower quantities of isoleucine compared to meat products such as beef and chicken (Sosulski and Imafidon, 1990). The amino acid profile of milk may therefore be more conducive to supporting a rise in circulating IGF-1 levels.’

Protein ingestion increases myofibrillar protein synthesis after concurrent exercise.

Our results show that a concurrent training session promotes anabolic adaptive responses and increases metabolic/oxidative mRNA expression in the skeletal muscle. PRO ingestion after combined resistance and endurance exercise enhances myofibrillar protein synthesis and attenuates markers of muscle catabolism and thus is likely an important nutritional strategy to enhance adaptation responses with concurrent training.