Nutrient intake and protein metabolism: responses to feeding.

Lean tissue growth occurs when the rate of protein synthesis exceeds the rate of protein breakdown. Although absolute rates of protein synthesis and breakdown rise during growth from birth to maturity fractional rates fall. Both these processes are sensitive to nutrient intake but responses to feeding vary greatly amongst different tissues. Protein, carbohydrate and fat can all stimulate body protein accretion in immature animals and in children but the mechanisms by which they do so, and the energy expenditures involved, seem to be different.