The effect of glycomacropeptide-based foods upon blood phenylalanine control in adults and children with phenylketonuria

Abstract

Conventional treatment for phenylketonuria restricts dietary phenylalanine to ‘control’ plasma phenylalanine concentrations. Its widespread adoption has largely eradicated the severe neurocognitive defects that previously characterised phenylketonuria. However, interest in alternative treatments continues as deficits in intelligence and other health outcomes remain problematic, conventional treatment has limitations and adherence proves difficult. Glycomacropeptide-based foods (GMP) are a novel treatment that may improve the satiety and acceptability of dietary treatment and address suboptimal health outcomes. However, glycomacropeptide contains some phenylalanine, raising safety concerns regarding its effect on plasma phenylalanine in adults and particularly children who tolerate less phenylalanine. This narrative review attempted to resolve these concerns. Its findings suggest adults and children can maintain control on GMP but individualised titrations, adjusting the amount of GMP consumed whilst monitoring plasma phenylalanine, are necessary in children. Equivalent control is a supportive finding given GMPs many advantages but this must be viewed cautiously as only seven studies were located, predominantly employing bias-prone, heterogeneous designs. GMPs effect upon control thus requires clarification via a systematic review using evidence-based, transparent methods to synthesize the entire evidence base and consider the impact of design quality, bias and heterogeneity upon results.