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ORIGINAL RESEARCH COMMUNICATION |
1 From the Research Institute, The Hospital for Sick Children, Toronto, Canada (JMT, MAH, RE, MR, VL, and PBP); the Department of Nutritional Sciences, University of Toronto, Toronto, Canada (PBP); and the Department of Agricultural, Food and Nutritional Science, University of Alberta, Alberta, Canada (ROB)
Background: Current total sulfur amino acid (TSAA) requirements of children are based on a factorial estimate that involves several assumptions.
Objective: 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.
Design: 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.
Results: 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.
Conclusions: 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.
Key Words: Total sulfur amino acid • methionine • indicator amino acid oxidation • amino acid requirement • stable isotope • phenylalanine • children
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