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American Journal of Clinical Nutrition, Vol. 86, No. 2, 360-365, August 2007
© 2007 American Society for Nutrition

ORIGINAL RESEARCH COMMUNICATION

Lysine requirement of healthy school-age children determined by the indicator amino acid oxidation method1,2,3

Rajavel Elango, Mohammad A Humayun, Ronald O Ball and Paul B Pencharz

1 From the Research Institute, The Hospital for Sick Children, Toronto, Canada (RE, MAH, and PBP); the Department of Nutritional Sciences, University of Toronto, Canada (PBP and ROB); and the Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada (ROB and PBP)

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 (F13CO2) 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 F13CO2 data, which identified a breakpoint (requirement) at minimal F13CO2 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 ({approx}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.

Key Words: Lysine • indicator amino acid oxidation • amino acid requirements • stable isotopes • children




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R. Elango, R. O. Ball, and P. B. Pencharz
Indicator Amino Acid Oxidation: Concept and Application
J. Nutr., February 1, 2008; 138(2): 243 - 246.
[Abstract] [Full Text] [PDF]


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