A Physiological Study to Determine the Enteral Threonine Requirements in Infants Aged 1 to 6 Months

INTRODUCTION

Threonine is an indispensable AA that must come from dietary sources. It is critical in the production of mucins in the gut (Law, Bertolo et al. 2007) and contributes significantly to collagen, elastin and tooth enamel formation (Kramsch, Franzblau et al. 1971, Robinson, Lowe et al. 1975). The current adequate intake (AI) for threonine in infants proposed by the Institute of Medicine, Food and Nutrition Board, in the 2005 Dietary Reference Intakes (DRIs) for macronutrients is based on a factorial approach due to the lack of conclusive empirical data. Studies that lead to the determination of amino acid (AA) requirements for infants used the nitrogen analysis technique and were performed over 20 years ago (Snyderman, Norton et al. 1959). Methodological advances have made it possible to determine AA requirements in humans with a more precise technique (Zello, Wykes et al. 1995). However, no studies of threonine requirement in infants (1- 6mo of age) with the use of the newer stable-isotope methods have been reported.

To accurately determine amino acid requirements, it is necessary to provide a range of amino acid intakes. For ethical reasons, infants cannot be fed very low or high test amino acid diets for prolonged periods of time. The minimally invasive IAAO method, initially developed in adults in our laboratory (Zello, Pencharz et al. 1993) and now used internationally (Huang, Hogewind-Schoonenboom et al. 2011) to determine amino acid requirements, overcomes this problem. The IAAO method takes less than 24 hours to conduct and has been used safely in parenterally fed neonates, enterally fed neonates, children and adults.

Our laboratory determined the enteral requirement of threonine in piglets (Bertolo, Chen et al. 1998) which was 0.42g/kg/d. We are able to extrapolate from this data, and propose that the enteral requirement for neonates would be 84 mg/kg/d. In this study we will be determining the enteral requirement for the 1 - 6 months old infant and predict that since growth slows and protein requirement decreases after the first month of life, the enteral requirement of infants will be similar to the DRI's AI of 73 mg/kg/d. Thus, the objective of this study is to determine the enteral Threonine requirement in infants from 1 to 6 months of age with the IAAO method.

SUBJECTS AND METHODS