Improved nutritional management of phenylketonuria by using a diet containing glycomacropeptide compared with amino acids.
BACKGROUND
Phenylketonuria (PKU) requires a lifelong low-phenylalanine diet that provides the majority of protein from a phenylalanine-free amino acid (AA) formula. Glycomacropeptide (GMP), an intact protein formed during cheese production, contains minimal phenylalanine.


OBJECTIVE
The objective was to investigate the effects of substituting GMP food products for the AA formula on acceptability, safety, plasma AA concentrations, and measures of protein utilization in subjects with PKU.


METHODS
Eleven subjects participated in an inpatient metabolic study with two 4-d treatments: a current AA diet (AA diet) followed by a diet that replaced the AA formula with GMP (GMP diet) supplemented with limiting AAs. Plasma concentrations of AAs, blood chemistries, and insulin were measured and compared in AA (day 4) and GMP diets (day 8).


RESULTS
The GMP diet was preferred to the AA diet in 10 of 11 subjects with PKU, and there were no adverse reactions to GMP. There was no significant difference in phenylalanine concentration in postprandial plasma with the GMP diet compared with the AA diet. When comparing fasting with postprandial plasma, plasma phenalyalanine concentration increased significantly with the AA but not with the GMP diet. Blood urea nitrogen was significantly lower, which suggests decreased ureagenesis, and plasma insulin was higher with the GMP diet than with the AA diet.


CONCLUSIONS
GMP, when supplemented with limiting AAs, is a safe and highly acceptable alternative to synthetic AAs as the primary protein source in the nutritional management of PKU. As an intact protein source, GMP improves protein retention and phenylalanine utilization compared with AAs.
van Calcar
Sandra C
SC
Waisman Center, University of Wisconsin, Madison, WI 53706, USA.
MacLeod
Erin L
EL
Gleason
Sally T
ST
Etzel
Mark R
MR
Clayton
Murray K
MK
Wolff
Jon A
JA
Ney
Denise M
DM
D000293:Adolescent; D000328:Adult; D000596:Amino Acids / Q000008:administration & dosage* / Q000097:blood* / Q000378:metabolism; D001774:Blood Chemical Analysis; D001806:Blood Urea Nitrogen; D002648:Child; D003257:Consumer Product Safety; D018592:Cross-Over Studies; D005260:Female; D006020:Glycopeptides / Q000008:administration & dosage* / Q000009:adverse effects / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D017060:Patient Satisfaction; D010649:Phenylalanine / Q000097:blood; D010661:Phenylketonurias / Q000097:blood* / Q000178:diet therapy*; D019518:Postprandial Period; D016896:Treatment Outcome; D055815:Young Adult
D000596:Amino Acids; D006020:Glycopeptides; D007328:Insulin; D010649:Phenylalanine