How to Create a PKU-Friendly Diet

By Monique Ryan, MS, RD, CSSD, LDN
Three young friends - Feeding the Child with PKU


March is National Nutrition Month, when the Academy of Nutrition and Dietetics reminds everyone to return to the basics of healthy eating. It is also the time of year when the Academy celebrates expertise of registered dietitian nutritionists as the food and nutrition experts.

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. "An infant will have to consume a special phenylalanine-free formula for the first year of life," says Sarah Krieger, MPH, RDN, LDN, former pokesperson for the Academy of Nutrition and Dietetics. However, some breast milk can be used in limited amounts.

Creating an 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 unique menu for the child. "The metabolic dietitian can create meal plans with modified food sources of protein low in phenylalanine and high in tyrosine, while providing adequate calories, vitamins and minerals to support growth," says Krieger. Because so many foods are off limits with PKU, the meal plans include special formulas which are often the primary source of calories and essential nutrients. Special phenylalanine-free foods are available for children and teens with PKU. The metabolic dietitian will create individual eating plans and modify them as needed to promote healthy growth and development.

The diet needs to be followed for life. "The individual with PKU will require blood monitoring to maintain serum phenylalanine levels," says Kreiger. 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 the 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 part of the management of his or her diet as early as possible. "A skilled dietitian, physician and psychologist team can address social issues with each stage of life," says Kreiger. "Knowledge is power and the more parents, and eventually the child, know how to live with PKU, then a healthy, productive life is possible."

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