PROTEIN-QUALITY AND UREA KINETICS IN PREPUBERTAL CHILEAN SCHOOLBOYS

Urea kinetics were measured non-invasively in 12 Chilean schoolboys ag ed 8-10 years who were receiving one of two diets, either predominantl y animal protein or predominantly vegetable protein. Both the diets pr ovided an equivalent level of gross protein, 1.2 g/kg/day. The study d iets were given for 10 days to enable adaptation to take place. On the eighth day a single oral dose of (NN)-N-15-N-15-urea, 100 mg, was giv en and the amount of label excreted as N-15(15)-urea in urine over the subsequent 48 hours was measured. There was little difference in any aspect of urea kinetics between the two diets with urea production (an imal, 173 +/- 50 mgN/kg/day; vegetable 179 +/- 53 mgN/kg/day), urea ex cretion (animal, 86 +/- 19 mgN/kg/day; vegetable, 105 +/- 13 mgN/kg/da y), urea nitrogen hydrolysis (animal, 87 +/- 49 mgN/ kg/day; vegetable , 74 +/- 42 mgN/kg/day), and the salvaged urea-nitrogen derived from h ydrolysis which returned to urea formation (animal, 12 +/- 5 mgN/kg/da y; vegetable, 17 +/- 9 mgN/kg/day) all being similar. A very high prop ortion of the salvaged nitrogen derived from urea hydrolysis was maint ained within the metabolic pool, about 80%, which was equivalent to 0. 4 g protein/kg/day. This is the first time urea kinetics have been mea sured in children of this age and shows that 57% of the urea produced is excreted in urine on average with about 43% of the urea-nitrogen be ing salvaged for further metabolic interaction. It is concluded that t he vegetable based protein diet taken habitually by Chilean children i s metabolically equivalent in terms of urea kinetics to a diet based u pon animal protein at this level of intake, but that high rates of sal vage of urea nitrogen are found on both diets.