Funding Information: This research was funded by Birmingham Children Hospital Charity Grant and Nutricia Research Grant Nutricia Ltd., Trowbridge, UK. Publisher Copyright: © 2025 by the authors.; Background: The rate at which amino acids (AAs) are absorbed from casein glycomacropeptide (CGMP) when given as a protein substitute in phenylketonuria (PKU) is unknown. This three-way randomised, controlled, crossover...