Tracer Kinetic Studies on a Methionine‐Supplemented Soy‐Based Infant Formula Using 1‐¹³C‐ and ¹⁵N‐Methionine as Tracers

Abstract

Summary:A tracer‐kinetic study using 1‐13C‐ and 15N‐labeled L‐methionine was conducted in order to measure the retention rate of free methionine added to commercially‐produced soy‐based infant formulas. Twelve male infants, fed on a soy formula, received a single‐pulse labeling by oral administration of L‐1‐13C‐methionine (5 mg/kg) and L‐15N‐methionine (10mg/kg). The abundance of expired 13C‐labeled CO2 was measured up to 7 h after administration at 15‐, 30‐, and 60‐min intervals. Additionally, enrichment of total 15N and 15N in urinary ammonia were determined up to 48 h after administration. Retention rates of the labeled carboxyl group amounted to an average of 91.2% (SD 4.1) of the intake. A similar retention rate was measured for the 15N‐label of methionine (90.0%, SD 4.3). The data point at the efficacy of methionine supplementation of soy‐based infant formulas.