Lysine requirement of healthy school-age children determined by the indicator amino acid oxidation method

Abstract

Background: The current Dietary Reference Intake (DRI) recommendations for lysine requirements in children are based on a factorial estimate. Objective: The objective of the current study was to determine the lysine requirement in healthy school-age children by measuring the oxidation of L-[1- 13C]phenylalanine to 13CO2 (F 13CO2) in response to graded intakes of lysine. Design: Five healthy school-age children randomly received each of 7 lysine intakes (5, 15, 25, 35 50, 65, and 80 mg·kg-1·d-1) along with an amino acid mixture to give a final calculated protein intake of 1.5 g·kg-1·d-1 and an energy intake of 1.7 X resting energy expenditure (REE). The mean lysine requirement was determined by applying 2-phase linear regression crossover analysis on F13CO 2 data, which identified a breakpoint (requirement) at minimal F 13CO2 in response to graded lysine intakes. Results: The mean and population-safe (upper 95% CI) lysine requirements were determined to be 35 and 58 mg·kg-1·d-1, respectively. Conclusions: The mean and population-safe lysine requirements for children are similar to those for adults (36 and 52 mg·kg-1·d -1, respectively), which suggests that the findings from the current study reflect predominantly the maintenance lysine requirements in children and not all requirements for growth. Therefore, to ensure age-appropriate growth in school-age children, we propose the addition of the requirement of lysine for growth (≈6 mg·kg-1·d-1) to the mean estimate. The new mean and population-safe lysine requirements are 41 and 58 mg·kg-1·d-1, respectively; these values are significantly higher than the current DRIs of 37 and 46 mg·kg -1·d-1, respectively. © 2007 American Society for Nutrition.