A kinetic model for growth as a function of time and nutritional status

A mathematical model for the programmed control of growth is developed. The growth considered is that of metabolically active tissue (MAT) and fat. The model postulates that the energy available after maintenance and activity needs have been met and after any necessary supporting tissue has been synthesized forms a common pool. Fat is synthesized from this pool with first order kinetics. The production of protein for MAT requires an intermediate called X. The kinetics of protein production are second order in which the magnitudes of the common energy pool and X are the reactants. X is formed from a precursor called Y and the total quantity of Y is fixed early in post-natal life. The model qualitatively accounts for the patterns of growth of both fat and MAT as functions both of age and of nutritional status. It also predicts both compensatory growth and a sigmoidal growth curve. Of the four rate constants in the model, one of them can be determined from data in which animals are grown on different constant planes of nutrition. Identification of the other rate constants requires data from the transient response to change in the plane of nutrition.