The main treatment for PKU includes:
- A lifetime diet with very limited intake of protein, because foods with protein contain phenylalanine
- Taking a PKU formula — a special nutritional supplement — for life to make sure you get enough essential protein (without phenylalanine) and nutrients that are crucial for growth and general health
A safe amount of phenylalanine differs for each person with PKU and can vary over time. In general, the idea is to consume only the amount of phenylalanine that's necessary for normal growth and body processes, but no more. Your doctor can determine a safe amount through:
- Regular review of diet records, growth charts and blood levels of phenylalanine
- Frequent blood tests that monitor phenylalanine levels as they change over time, especially during childhood growth spurts and pregnancy
- Other tests that assess growth, development and health
Your doctor may refer you to a registered dietitian who can help you learn about the PKU diet, make adjustments to your diet when needed, and offer suggestions on ways to manage PKU diet challenges.
Which foods to avoid
Because the amount of phenylalanine that a person with PKU can safely eat is so low, it's crucial to avoid all high-protein foods, such as:
Potatoes, grains and other vegetables that have protein will likely be limited.
Children and adults also need to avoid certain other foods and beverages, including many diet sodas and other drinks that contain aspartame (NutraSweet, Equal). Aspartame is an artificial sweetener made with phenylalanine.
Some medications may contain aspartame and some vitamins or other supplements may contain amino acids or skim milk powder. Check with your pharmacist about the contents of over-the-counter products or prescription medications.
Talk with your doctor or registered dietitian to learn more about your specific dietary needs.
Formula for people with PKU
Because of the restricted diet, people with PKU need to get essential nutrients through a special nutritional supplement. The phenylalanine-free formula provides protein and other essential nutrients in a form that's safe for people with PKU.
Your doctor and dietitian can help you find the right type of formula.
- Formula for babies and toddlers. Because regular infant formula and breast milk contain phenylalanine, babies with PKU instead need to consume a phenylalanine-free infant formula. A dietitian can carefully calculate the amount of breast milk or regular formula to be added to the phenylalanine-free formula. Parents introduce solid foods with low levels of phenylalanine to children with PKU on the same schedule used for other infants.
- Formula for older children and adults. Older children and adults continue to drink or eat a protein substitute formula daily, as directed by a doctor or dietitian. Your daily dose of formula is divided between your meals and snacks, instead of consumed all at once. The formula for older children and adults is not the same as the one used for infants, but it works on the same principle. It provides essential protein (amino acids) without phenylalanine and is continued for life.
The need for a nutritional supplement, especially if your child doesn't find it appealing, and the limited food choices can make the PKU diet challenging. But families need to make a firm commitment to this lifestyle change because it's the only way to prevent the serious health problems that people with PKU can develop.
Neutral amino acid therapy
Another possible addition to the PKU diet is a supplement called neutral amino acid therapy in powder or tablet form. This supplement may block some absorption of phenylalanine. This may be a treatment option for adults with PKU. Ask your doctor or dietitian if this supplement is appropriate for your diet.
The Food and Drug Administration (FDA) has approved the drug sapropterin (Kuvan) for the treatment of PKU. It works by increasing your tolerance to phenylalanine. The drug is for use in combination with a PKU diet. But it doesn't work for everyone with PKU.
In approving sapropterin, the FDA directed that studies continue because there are no long-term studies on the drug's efficacy and long-term safety.