Breakfast with glycomacropeptide compared with amino acids suppresses plasma ghrelin levels in individuals with phenylketonuria

Abstract

Phenylketonuria (PKU) requires a lifelong low-phenylalanine (phe) diet where protein needs are met by consumption of a phe-free amino acid (AA) formula; complaints of persistent hunger are common. Foods made with glycomacropeptide (GMP), an intact protein that contains minimal phe and may promote satiety, provide an alternative to AA formula. The objective was to assess the ability of a GMP breakfast to promote satiety and affect plasma concentrations of AAs, insulin, and the appetite stimulating hormone ghrelin in those with PKU, when compared to an AA-based breakfast. Eleven PKU subjects (8 adults and 3 boys ages 11-14) served as their own controls in an inpatient metabolic study with two 4-day treatments: an AA-based diet followed by a diet replacing all AA formula with GMP foods. Plasma concentrations of AAs, insulin and ghrelin were obtained before and/or 180 min after breakfast. Satiety was assessed using a visual analog scale before, immediately after and 150 min after breakfast. Postprandial ghrelin concentration was significantly lower (p=0.03) with GMP compared to an AA-based breakfast, with no difference in fasting ghrelin. Lower postprandial ghrelin concentrations were associated with greater feelings of fullness after breakfast suggesting greater satiety with GMP compared to AAs. Postprandial concentrations of insulin and total plasma AAs were higher after a GMP breakfast compared to an AA-based breakfast consistent with slower absorption and less degradation of AAs from GMP. These results show sustained ghrelin suppression, and suggest greater satiety with ingestion of a meal containing GMP compared with AAs.

Copyright 2010 Elsevier Inc. All rights reserved.

Figures

Figure 1

Significant changes in plasma concentrations of ghrelin, insulin and amino acids were apparent with the GMP diet. Ghrelin and insulin values represent equal volumes of plasma combined for each subject from days 3+4 for the AA breakfast, days 7+8 for the GMP breakfast. Sum of postprandial (PP) plasma AA values on the last day of the AA diet (day 4) and last day of the GMP diet (day 8). All values are means ± SEM; n=6 for ghrelin fasting values. * Indicates significantly different from postprandial ghrelin with AA breakfast (p=0.03, paired t-test, pairing on subject; n=10) ** Indicates moderately significant difference from insulin with the AA breakfast (p=0.053, paired t-test, pairing on subject; n=10) *** Indicates significantly different from sum of plasma AAs with the AA breakfast (p=0.049, paired t-test, pairing on subject; n=11)

Figure 2

Relationship between plasma ghrelin concentrations 180 minutes after the start of breakfast and feeling of fullness 2 hr after breakfast. Lower postprandial ghrelin was associated with greater feeling of fullness. Lines represent least squares regression lines fitted to individual diet treatment data; AA breakfast is dashed line and GMP breakfast is solid line. Lines are significantly different. Using backward elimination with a mixed effects model, the best model predicting postprandial fullness scores included diet treatment, postprandial ghrelin and the interaction between ghrelin and diet treatment.