PKU Challenges

With medical foods, there’s still room for improvement

Many people with PKU struggle to adhere to their diet and medical foods. And even if they are adherent, the free AAs in medical foods may not be absorbed like natural proteins, potentially leading to periods of lower plasma AA concentration levels.1,2

Medical foods often have unpleasant flavor and aftertaste3

  • Free AAs commonly found in medical foods have a strong flavor, often leading to bad breath and an unpleasant aftertaste4
  • Moreover, many patients report “taste fatigue” with their current medical food since it must be consumed multiple times a day, every day, for life4,5

Extended periods of lower plasma AA concentration levels with free AAs3

Even with PKU patients who adhere to their diet, issues may remain. The quick absorption time of free AAs results in rapid AA oxidation and elimination. This can lead to low plasma concentration of AAs for extended periods of time, particularly overnight.3

Absorption kinetics of AAs over ~24 hours3,6


With free AAs, fast absorption means longer periods of lower plasma concentration of AAs throughout the day

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Adapted from Gropper and Acosta. JPEN. 1991;15(1):48-53.

Extended periods of low plasma AA concentration levels may cause muscles to break down

During extended fasting periods at night, patients may experience catabolic episodes, where muscle breaks down, releasing Phe into the bloodstream and raising Phe levels.2

For more information

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References: 1. Giarratana N, Gallina G, Panzeri V, et al. A new Phe-free protein substitute engineered to allow a physiological absorption of free amino acids for phenylketonuria. JIEMS. 2018;6:1-9. 2. Giarratana N, Giardino L, Bighinati A, et al. In vivo metabolic responses to different formulations of amino acid mixtures for the treatment of phenylketonuria (PKU). Int J Mol Sci. 2022;23(2227):1-12. doi:10.3390/ijms23042227 3. Scheinin M, Junnila J, Reiner G, et al. Nitrogen balance after the administration of a prolonged-release protein substitute for phenylketonuria as a single dose in healthy volunteers. Nutrients. 2021;13(3189):1-10. doi:10.3390/nu13093189 4. MacDonald A, Ashmore C, Daly A, et al. An observational study evaluating the introduction of a prolonged-release protein substitute to the dietary management of children with phenylketonuria. Nutrients. 2020;12(2686):1-11. doi:10.3390/nu12092686 5. MacDonald A, van Rijn M, Feillet F, et al. Adherence issues in inherited metabolic disorders treated by low natural protein diets. Ann Nutr Metab. 2012;61(4):289-295. 6. Gropper SS, Acosta PB. Effect of simultaneous ingestion of l-amino acids and whole protein on plasma amino acid and urea nitrogen concentrations in humans. JPEN. 1991;15(1):48-53.