Abstract
The main source of nitrogen (N) for patients with phenylketonuria (PKU) is a phenylala-nine-free amino acid mixture. It is recommended that the total daily amount is divided into a minimum of three single doses. Adolescent patients in particular tend to consume the protein supplement in just one or two doses. A complete anabolic metabolization of these large amounts of amino acids is impossible. Therefore, we measured the nitrogen retention in 9 patients with PKU and one with hyperphenylalaninemia. On day I of the study, all patients consumed their amino acid mixture in just one or two doses. On day 2, they ingested their amino acid mixture in three equal portions with their principal meals. Nutrition protocols were established to determine the total intake of N on both days. 24-h urine samples were collected on both days and the N content was determined using an elemental analyzer. Urine N excretion was 6-3-12-4 g/24 h on day 1, and 4-7-10-8 g/24 h on day 2 of the study. In eight patients, excretion of N decreased TO-2-8 g/24 h when the total amount of amino acid mixture was given in smaller and more frequent doses, presumably reflecting a decrease in oxidative metabolism of amino acids. In conclusion, all physicians dealing with PKU patients should stress the importance of taking the daily amount of amino acid mixtures in at least three equal doses, as recommended.
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