Food restriction and lysine supplementation alter growth, RNA, DNA, and protein contents of skeletal muscle.

Efficacy of supplementing total protein or a limiting amino acid to maintain muscle development during food restriction was examined in growing rats. Male rats weighing 108 +/- 8 g were assigned to one of five diet groups plus an initial group. Animals were fed either a wheat gluten-based diet or the wheat gluten-based diet supplemented with adequate levels of lysine. These diets were fed ad libitum or at a 75% restricted level. One restricted group was fed a high gluten diet designed to meet lysine requirements but at the restricted energy level. Rats were fed these diets for 6 weeks. Lysine supplementation resulted in higher levels of protein, RNA, and DNA in skeletal muscle and liver of animals fed ad libitum. Food restriction resulted in loss of protein and RNA from liver and skeletal muscle and lower ratios of protein/DNA. Initial DNA contents of plantaris and soleus muscles were not affected by food restriction; however, hepatic DNA was reduced. Supplementation of lysine to animals restricted in food intake failed to improve growth of skeletal muscle or liver, and resulted in lower protein contents in liver (11%), plantaris (6%), and soleus (38%). Increasing total protein intake for the animals with the restricted intake resulted in a higher RNA/DNA ratio without a parallel increase in protein in liver or muscle. This study demonstrates that during severe food restriction skeletal muscle DNA is preserved which maintains high potential for growth recovery. This study also indicates that during severe, prolonged food restriction supplementation of protein or limiting amino acids results in lower tissue protein contents.