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How to Create a PKU-Friendly Diet

Contributors: Monique Ryan, MS, RD, CSSD, LDN

Published: April 24, 2017

Reviewed: July 08, 2016

A young boy with PKU (Phenylketonuria) is eating a plate of fresh fruit as part of his PKU-friendly diet.
Andrey Zhuravlev/iStock/Getty Images Plus

Phenylketonuria, or PKU, is a genetically inherited birth defect that causes an unwanted buildup of the amino acid phenylalanine in the blood. This buildup occurs because the enzyme that routinely converts one amino acid, phenylalanine, to another amino acid, tyrosine, is absent or deficient. Phenylalanine then accumulates in the blood and is toxic to brain tissue.

PKU at Birth

Babies born in the United States are screened for PKU with a blood test so treatment can begin immediately and prevent the adverse side effects of the condition, such as declining intelligence, neurological deterioration, stunted growth, hyperactivity and seizures. A treatment team typically consists of a metabolic dietitian, physician, geneticist and psychologist as an infant is monitored during different phases of growth and development in childhood to an adult.

A strict diet limited in phenylalanine is the main treatment for PKU. Phenylalanine is found in most protein-containing foods such as milk, eggs, cheese, nuts, soybeans, chicken, beef, pork, beans and fish. While some breast milk can be used in limited amounts, infants with PKU rely on a special metabolic formula that is phenylalanine-free for the first year of their life.

Creating a Unique Meal Plan

As the infant grows and becomes developmentally ready for solid foods, a registered dietitian nutritionist with expertise in PKU will create a customized menu for the child. A metabolic RDN will work with the child and their family to ensure the diet provides the calories, nutrients, vitamins and minerals that are essential for optimal growth and development, while focusing on including low-phenylalanine and high-tyrosine foods. Because so many foods are off limits with PKU, the meal plans include special formulas that are often the primary source of calories and essential nutrients. Special phenylalanine-free foods are available for children and teens with PKU. The metabolic RDN will monitor and modify the customized eating plan as needed to promote healthy growth and development.

The PKU-friendly diet needs to be followed for life to maintain serum phenylalanine levels, which will be checked during routine blood draws. High serum phenylalanine levels can result in lack of concentration, shortened attention span and memory problems. In conjunction with blood monitoring, the metabolic dietitian will regularly review diet records or food journals and growth charts, making adjustments to the eating plan as needed.

Parents of children with PKU need to be creative with foods and use available PKU cookbooks. Get help with menu planning from a metabolic dietitian and plan ahead for eating out, school lunches, potlucks, trips and vacations, and other special events. Try to center special occasions around activities rather than food, and encourage your child to be involved in managing their diet as early on as possible.

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