Returning to the PKU diet

Maintaining blood Phe levels in the range of  120–360 μmol/L (2–6 mg/dL) at all ages is essential for all people with PKU.

In my teens and early 20s, I got into the habit of overeating things that were “sometimes-” or “in-small-amounts-” foods, like potatoes, chips, rice, real pasta, and bread. In my 20s, I got insurance [and] wanted to be ready to have children when the time came. So I buckled down and started doing the diet I did as a kid. I stopped eating regular bread or pasta, even if I could “have a little.” It's much easier to just eliminate them and supplement with low-pro foods. Figure out what you need to do to in your life to achieve the proper Phe levels and health. It takes time to figure this out...but don't give up.

Jen, 38 years old

Recognizing the importance of maintaining your blood Phe levels to be within the recommended range throughout your life is the first step towards regaining control of your diet.

Did you know that adults with PKU are at a greater risk for executive function, attention, social, and emotional difficulties even if treated continuously with a low-Phe diet from infancy? See the Adult PKU and the Brain section if you are impacted by these difficulties.

For more ideas, check out our tips for returning to your low-Phe diet.


People with PKU report a variety of reasons for relaxing their diets, from “wanting to be normal” to “the cost of low-protein food and formula.” Previous treatment guidelines allowed for the relaxation of the low-Phe diet once a person with PKU reached their teen years. Since 2000, however, it is recommended that all individuals with PKU remain on dietary treatment for life.

If you have relaxed your diet, you may feel the effects of having high Phe levels. People with PKU who have high Phe levels report feeling anxious and mentally "fuzzy.” Medical studies have shown related increases in executive function deficits (such as difficulties with concentration, memory, and planning) and psychiatric symptoms (such as depression, anxiety, and phobias). Unfortunately, these very symptoms can make the return to and management of the low-Phe diet more difficult.

Visiting a PKU clinic near you for advice on how to resume a low-Phe diet. Clinics have a variety of resources available and can help you establish a plan to slowly get back on a diet that works for you. Find a PKU clinic for teens and adults near you.

Exploring the new products available that may make resuming the diet easier. These include tastier formula and more low-protein foods, as well as medicine that may work in conjunction with your diet to keep your Phe levels in control.

You will feel better on diet!

Make peace with your formula. Love vegetables. I drink my formula every day religiously.

31-year-old woman with PKU

Drink your formula! Or [consume your] bar or whatever Phe-free protein replacement supplement you take. It makes everything else better/easier.

Jen, 38 years old

Before the year 2000 when the National Institutes of Health (NIH) recommended that all people with PKU maintain their low-Phe diet for life, people discontinued their diets once their doctor felt their brain was fully developed.

Learn to recognize the impact high Phe levels may be having on your life. Do you:

  • Have difficulties paying attention or planning?
  • Have tremors?
  • Experience depression, anxiety or phobias?

Call your local PKU clinic. They can help get you back on track with your low-Phe diet with a plan that suits you and your lifestyle.

Many people don’t fully recognize how high Phe levels were impacting them until they resumed their diet.

I felt like I was in a fog.

Adult with PKU reflecting on when she was off her low-Phe diet.