Daly A, Evans S, Chahal S, Santra S, Pinto A, Gingell C, Rocha JC, van Spronsen F, Jackson R, MacDonald A.
The Effect of Glycomacropeptide versus Amino Acids on Phenylalanine and Tyrosine Variability over 24 Hours in Children with PKU: A Randomized Controlled Trial. Nutrients.
2019 Feb 28;11(3).

Glycomacropeptide is a protein that is a by-product of cheese production. It is low in phenylalanine, but it is not phenylalanine free. It typically contains 36 mg per 20 g protein

equivalent. For patients prescribed 60 g/day protein equivalent from this source of protein substitute, it will supply 108 mg/day Phe (2 x 50 mg phenylamine exchanges), which may affect blood Phe control.

The aim of this randomised controlled cross-over study was to assess the blood Phe variability in children with PKU, comparing conventional amino supplements with GMP. GMP was studied under two conditions: a) no dietary adjustment for the Phe content of GMP, and b) dietary adjustment for the Phe content of GMP by lowering dietary Phe intake. 19 children with PKU (aged 6 to 16 years) were recruited from Birmingham Children’s Hospital. This study demonstrated that the Phe supplied by GMP adversely affected blood Phe control in children.

GMP should be used with caution in children less than 12 years of age, as there is a risk of Phe concentrations increasing beyond target recommendations.

Read the full research here.


Evans S,
Development of national consensus statements on food labelling interpretation and protein allocation in a low phenylalanine diet for PKU;
Orphanet Journal of Rare Diseases (2019) 14:2

The PKU diet regime is a low phenylalanine diet, ie very low in protein containing foods, and when the phenylalanine content of food is known a phe exchange value is allocated, otherwise, protein values are used, which can mean interpreting the label on manufactured foods. The complexity of the diet has evolved over 20-30 years and details have only just been agreed by specialists because of this complexity.  Foods are allocated into either foods to be avoided, foods allowed freely (without measurement or counting), and foods which must be weighed measured and portions consumed must be counted.

In 2015, British Inherited Metabolic Disease Group (BIMDG) dietitians (n = 70) were sent a multiple-choice questionnaire on the interpretation of protein from food-labels and the allocation of different foods. Based on majority responses, 16 statements were developed. Over 18-months, using Delphi methodology, these statements were systematically reviewed and refined with a facilitator recording discussion until a clear majority was attained for each statement. In Phase 2 and 3 a further 7 statements were added.

Read the full research here.