Lysine kinetics in preterm infants: The importance of enteral feeding

Introduction: Lysine is the first limiting essential amino acid in the diet of newborns. First pass metabolism by the intestine of dietary lysine has a direct effect on systemic availability. We investigated whether first pass lysine metabolism in the intestine is high in preterm infants, particularly at a low enteral intake. Patients and methods: Six preterm infants (birth weight 0.9 (0.1) kg) were studied during two different periods: period A (n=6): 40% of intake administered enterally, 60% parenterally; lysine intake 92 (6) μmol/(kgxh); and period B (n=4): 100% enteral feeding; lysine intake 100 (3) μmol/(kgxh). Dual stable isotope tracer techniques were used to assess splanchnic and whole body lysine kinetics. Results: Fractional first pass lysine uptake by the intestine was significantly higher during partial enteral feeding (period A 32 (10)% v period B 18 (7)%; p<0.05). Absolute uptake was not significantly different. Whole body lysine oxidation was significantly decreased during full enterai feeding (period A 44 (9) v period B 17 (3) μmol/(kgxh); p<0.05) so that whole body lysine balance was significantly higher during full enteral feeding (period A 52 (25) v period B 83 (3) μmol/(kgxh); p<0.05). Conclusions: Fractional first pass lysine uptake was much higher during partial enteral feeding. Preterm infants receiving full enteral feeding have lower whole body lysine oxidation, resulting in a higher net lysine balance, compared with preterm infants receiving partial enteral feeding. Hence parenterally administered lysine is not as effective as dietary lysine in promoting protein deposition in preterm infants.

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