Effect of varying energy and protein intakes on some biochemical parameters of protein metabolism

Three biochemical parameters of protein metabolism, i.e., urea index, urinary 3-methyl histidine, and urinary hydroxyproline, were studied in preschool children fed varying levels of protein and energy. The effect of varying protein and energy intakes on urinary 3-methyl histidine was also studied in adults. Varying protein and energy intakes had no significant effect on urea index and urinary 3-methyl histidine excretion as long as positive nitrogen balance was maintained. However, these two parameters decreased only when intakes of protein and energy were below maintenance levels, which resulted in a negative nitrogen balance. Urea index and urinary 3-methyl histidine excretion can be used therefore as an index to identify those malnourished children whose protein and/or energy intakes are grossly inadequate, resulting in negative nitrogen balance. Hydroxyproline excretion was responsive to alterations in protein intakes rather than to changes in energy intakes and the alteration in its excretion was small for large changes in protein intakes.