Low Protein Formula: Consequences of Quantitative Effects of Pre-analytical Factors on Amino Acid Concentrations in Plasma of Healthy Infants.

Abstract

Quantifying pre-analytical effects of postprandial sampling delay and daily protein intake on plasma amino acid concentrations in healthy infants fed formula with low protein content (1.8-1.9g/100kcal). Intake of formula with higher protein content bears a risk for later obesity (Kirchberg, J Clin Endocrinol Metab 100(1):149-158, 2015). Formulas containing less than 1.8g protein might be adequate but not safe (Fomon, J Pediatr Gastroenterol Nutr 28:495-501, 1999). With on-demand feeding reproducible controls of indispensible amino acid concentration cannot be made at trough level. Data of 102 healthy infants aged 1 month and 79 aged 4 months fed formula with low protein content were obtained from a previous study (Haschke-Becher, J Inherit Metab Dis 39(1):25-37, 2016). They were analysed by multiple regression. Independent variables were the postprandial sampling delay from 2.25 to 4.5h and the daily protein intake. Dependant variables were the amino acid concentrations. The combined effect was calculated with the natural logarithm of the amino acid concentration. Most amino acids fitted a significant exponential decrease due to the sampling delay, except of aspartate, citrulline, glutamine, glutamate, histidine, tryptophan and tyrosine at 1 month; and at 4 months except of citrulline, glutamine, glutamate, glycine and ornithine. Significant effects of protein intake were found for lysine and serine at 1 month and for glutamate at 4 months of age. Lowest limits of significant amino acid concentrations were calculated by extrapolation of sampling delay to 5h and using the 10th percentile after back-transformation to μmol/L. A procedure to avoid the pitfall of overestimating amino acid concentration is presented.