People with the medical condition phenylketonuria have to follow a special phenylalanine-free diet. While this diet can be highly restrictive, it is necessary to prevent major health complications. The exact structure of your phenylalanine-free diet depends on your specific health conditions, but in all cases you cannot eat phenylalanine-rich foods.
Phenylketonuria
PKU is a genetic disorder present from birth. People born with PKU cannot produce the enzyme phenylalanine hydroxylase. This enzyme breaks down the amino acid pheylalanine, so people with PKU need to consume a diet that prevents the buildup of this amino acid. In most Western countries, children are screened at birth for PKU and placed on a phenylalanine-free diet from infancy. Affected individuals who do not go on this type of diet are at risk for mental retardation, seizures and behavioral problems, as excess phenylalanine builds up in the bloodstream. People on a phenylalanine-free diet do need to take in small amounts of phenylalanine, but only enough to maintain the biological processes that need it.
Dietary Restrictions
A phenylalanine-free diet is low in protein, since this amino acid is found in many protein sources. Meat, chicken, fish, eggs, dairy products, beans, tofu, chocolate and nuts are forbidden on a phenylalanine-free diet. Foods containing the artificial sweetener aspartame are also off-limits because this compound converts to phenylalanine in the body. Babies with PKU need a special phenylalanine-free formula because they cannot tolerate normal formula or breast milk. The specific amount of phenylalanine a person with PKU can tolerate differ from person to person, so some people with the disease can eat things another cannot.
Allowed Foods
A phenylalanine-free diet focuses on special low-protein bread and pastas. Low-protein vegetables and fruits are also allowed. You can eat some other foods in limited amounts, such as rice, cookies and fruits and vegetables containing moderate amounts of protein. A nutritional substitute formula for children and adults is also available to supplement the solid foods on a phenylalanine-free diet. This formula is different from the baby formula used in infancy.
Considerations
A phenylalanine-free diet should be designed in consultation with a registered dietitian to ensure you meet all of your nutritional needs while providing you with the minimal intake of phenylalanine you need to survive. Most doctors recommend continuing a phenylalanine-free diet for life, but some people choose to stop the diet in adolescence or adulthood. Women who have PKU or a family history of the disease should go on a phenylalanine-free diet during pregnancy.
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