Total sulfur amino acid requirement of healthy school-age children as determined by indicator amino acid oxidation technique

Abstract

Current total sulfur amino acid (TSAA) requirements of children are based on a factorial estimate that involves several assumptions. The objective was to determine the TSAA requirement (methionine alone) of healthy school-age children by measuring the appearance of 13CO2 (F13CO2) in breath after the oxidation of l-[1-13C]phenylalanine in response to graded methionine intakes. Six healthy school-age children randomly received each of 6 methionine intakes (0, 5, 10, 15, 25, and 35 mg.kg(-1).d(-1)) along with an amino acid mixture to give a final protein intake of 1.5 g.kg(-1).d(-1) and an energy intake of 1.7 x resting energy expenditure. The diet was devoid of cysteine. The mean TSAA requirement was determined by applying a biphase linear regression crossover analysis on F13CO2 data, which identified a breakpoint at minimal F13CO2 in response to graded methionine intakes. The mean and population-safe (upper 95% CI) intakes of TSAA (as methionine) were determined to be 12.9 and 17.2 mg.kg(-1).d(-1), respectively. The current study suggests that children of this age group have a mean TSAA requirement similar to that of adults (12.6 mg.kg(-1).d(-1)). Therefore, it is valid to use a factorial approach, which assumes that maintenance requirements in childhood are similar to adult requirements, to estimate TSAA requirements in school-age children.