The PKU Diet
People with PKU need to follow a diet that limits foods with phenylalanine. The diet should be followed carefully and be started as soon after birth as possible. In the past, experts believed that it was safe for people to stop following the diet as they got older. However, they now recommend that people with PKU stay on the diet throughout their lives for better physical and mental health.
It is especially important for a pregnant woman with PKU to strictly follow the low-phenylalanine diet throughout her pregnancy to ensure the healthy development of her infant.
People with PKU need to avoid various high-protein foods, including:
- Milk and cheese
- Chicken, beef, or pork
People with PKU also need to avoid the sweetener aspartame, which is in some foods, drinks, medications, and vitamins. Aspartame releases phenylalanine when it is digested, so it raises the level of phenylalanine in a person’s blood.1
Often, people with PKU also have to limit their intake of lower-protein foods, such as certain fruits and vegetables. However, a PKU diet can include low-protein noodles and other special products.
The amount of phenylalanine that is safe to consume differs for each person. Therefore, a person with PKU needs to work with a health care professional to develop an individualized diet. The goal is to eat only the amount of phenylalanine necessary for healthy growth and body processes but not any extra. Frequent blood tests and doctor visits are necessary to help determine how well the diet is working. Some relaxation of the diet may be possible as a child gets older, but the recommendation today is lifelong adherence to the diet.Following the diet is especially important during pregnancy.
However, the PKU diet can be very challenging. Getting support from friends and family or a support group can help. Sticking with the diet ensures better functioning and improved overall health.
A PKU Formula
People who follow the PKU diet will not get enough essential nutrients from food. Therefore, they must drink a special formula.
A newborn who is diagnosed with PKU should receive special infant formula. The formula may be mixed with a small amount of breast milk or regular infant formula to make sure the child gets enough phenylalanine for normal development but not enough to cause harm.
Older children and adults receive a different formula to meet their nutritional needs. This formula should be consumed every day throughout a person’s life.
In addition to the formula, health care professionals may recommend other supplements. For example, fish oil may be recommended to help with fine motor coordination and other aspects of development.1
Medication for PKU
The U.S. Food and Drug Administration (FDA) has approved the drug sapropterin dihydrochloride (Kuvan®) for the treatment of PKU. Kuvan® is a form of BH4, which is a substance in the body that helps break down phenylalanine. However, having too little BH4 is only one reason a person may not break down phenylalanine. Therefore, Kuvan® only helps some people reduce the phenylalanine in their blood. Even if the medication helps, it will not decrease the phenylalanine to the desired amount and must be used together with the PKU diet.
When the FDA approved Kuvan®, the agency suggested that research on the medication continue to determine its long-term safety and effectiveness.
Other Treatments for PKU
NICHD-supported researchers and other scientists are exploring additional treatments for PKU. These treatments include large neutral amino acid supplementation, which may help prevent phenylalanine from entering the brain, and enzyme replacement therapy, which uses a substance similar to the enzyme that usually breaks down phenylalanine. Researchers are also investigating the possibility of using gene therapy, which involves injecting new genes to break down phenylalanine. That would result in the breakdown of phenylalanine and decreased blood phenylalanine levels.