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Phenylalanine kinetics differ between formula-fed and human milk-fed preterm infants.
Pauline B Darling1, Michael Dunn, G Sarwar Gilani
1Research Institute, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada. darlingp@smh.toronto.on.ca
The Journal of Nutrition
|October 7, 2004
Summary
Formula-fed preterm infants show reduced phenylalanine catabolism, leading to higher plasma levels compared to breastfed infants. This suggests impaired amino acid metabolism in formula-fed infants.
Area of Science:
- Biochemistry
- Neonatology
- Nutritional Science
Background:
- Infants fed casein-dominant formulas exhibit higher plasma phenylalanine and tyrosine than those fed mother's milk.
- Formula-fed preterm infants demonstrate a reduced capacity to degrade threonine compared to breastfed infants.
Purpose of the Study:
- To investigate phenylalanine catabolism in preterm infants fed formulas with varying whey:casein ratios compared to mother's milk.
- To determine if formula composition affects phenylalanine metabolism and plasma concentrations in preterm infants.
Main Methods:
- Utilized a [1-(13)C]phenylalanine tracer to measure phenylalanine oxidation via (13)CO(2) production in breath.
- Compared plasma phenylalanine concentrations and oxidation rates in preterm infants fed different formula compositions (whey:casein 60:40, 40:60, 20:80) versus mother's milk.
Main Results:
- Plasma phenylalanine concentrations significantly increased with higher casein content in formulas.
- Formula-fed infants showed a positive correlation between phenylalanine intake and oxidation, but insufficient to prevent plasma level increases with high-casein formula.
- Phenylalanine oxidation was significantly lower in formula-fed infants (30.7% of intake) compared to those fed mother's milk (39.1% of intake).
Conclusions:
- Formula-fed preterm infants exhibit down-regulated in vivo catabolism of phenylalanine, contributing to elevated plasma concentrations.
- Impaired catabolism of essential amino acids, including phenylalanine and threonine, may explain metabolic differences between formula-fed and breastfed preterm infants.