The PKU diet is always about a careful balance. You need to keep Phe low, while making sure your child gets enough nutrition and calories.

It may help to remember "the 3 Rs" – Restrict, Replace, and Record.

Restrict: Not too much Phe

Phe is important for growth and brain function.² Therefore, people with PKU must eat some Phe, but only as much as the doctor prescribes. The amount of Phe your child can eat is called his or her "Phe tolerance." It is different for each person with PKU. You need to restrict your child's Phe to this level.¹

Replace: The right amount of protein

Phe is found in most protein, so high-protein foods are not allowed. Instead, your child will have a formula that has everything else found in protein, except Phe. People with PKU have this formula every day with every meal. This will replace natural protein.¹

Record: Natural foods

Your child will also have some natural foods that are low in protein. Many of these are high in fat, sugar or starch. You will need to record what kinds of food and how much your child eats, in order to track his or her Phe intake. Share these notes with the dietitian. Get blood tests often, so you can make sure blood Phe stays low.

Next: Is PKU medication right for your child?