16 children with PKU who currently take a Phe-free/low Phe protein substitute (3 or 4 doses/day) will be recruited. Subjects will replace the last daily dose of their usual protein substitute with the study product for 7 days of the 28 day trial (either days 1-7 or days 22-28 based on random allocation). On the remaining study days, subjects will take an amino acid based protein substitute for all daily doses. There will be a 2 week washout period between study arms where subjects will take their usual protein substitute. The amount of study product prescribed will be calculated to provide the same amount of protein as their usual protein substitute. The last protein substitute (PS) dose of the day (amino acids or study product) will need to be taken between 7-9pm to allow an 8-10 hour fasting period overnight. Three finger prick blood spots will be collected and analysed for phenylalanine, tyrosine and BCAA at 5am, 6am and 7am on days -1, 0, 6, 7, 20, 21, 27 and 28. For all subjects, a second void urine sample will be collected on days 0, 7, 21 and 28 for analysis of urea and creatinine. A quality of sleep questionnaire will be completed by subjects or their carers on days 0, 7, 21 and 28 and a 24 hour food diary on days -1, 0, 6, 7, 20, 21, 27 and 28. Subject visits will be on days -2 (enrolment), 0, 7, 21 and 28 where the research dietitian will collect urine samples, blood spots, questionnaires and diaries.
This is a 2 arm, randomised, controlled, cross-over study in 16 children with PKU. Subjects who are currently taking a Phe free/low Phe protein substitute will be recruited for a 31-day trial.~Patients will be randomised to receive:~The study product for 7 days as their last dose of protein substitute for the day (at least one sachet with 15g PE) in an amount equivalent to their usual protein substitute PE; or~An amino acid protein substitute for all daily doses for 7 days; followed by a 2-week washout period on their usual protein substitute,~and then 7 days of the other study arm.~During this time, patients/caregivers will be asked to:~Collect 3 finger prick blood spots on days -1, 0, 6, 7, 20, 21, 27 and 28.~Collect urine sample, second void of the day on days 0, 7, 21 and 28.~Complete a questionnaire on sleep quality on day 0, 7, 21 and 28.~Complete a 24 hour food diary on days -1, 0, 6, 7, 20, 21, 27 and 28.~APR will supply the study product for participants free of charge.