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PKU and Your Diet

When you have phenylketonuria (PKU), you need to follow a lifelong special diet. Having PKU means your body can’t break down an amino acid called phenylalanine (Phe). Amino acids are building blocks of protein. This amino acid can build up in your blood. And if the levels get too high, it could harm your brain. But this is preventable. The key to staying healthy with PKU is limiting how much Phe you consume.

What is the PKU diet?

Phe is found in protein. To manage PKU, you need to limit the protein you get from food. Yet getting enough protein is vital for keeping your body working as it should. So you also need to eat a special protein mixture that’s high in protein but contains little or no Phe. Talk with healthcare provider or a metabolic dietitian about a safe, healthy eating plan for you.

How can this diet help you?

To stay your healthiest with PKU, you need to be careful about what you eat and drink. Keeping blood levels of Phe within a healthy target range helps protect your brain. People with PKU who stay on a special diet for life have better mental and physical health than those with don’t.

Does this diet have any risks?

This diet strictly limits how much protein you eat. When you don’t eat protein foods, you may also fall short on the other nutrients they provide. These nutrients may be included in the special protein mixture you use. Or your provider may advise taking them in supplements. For example, you may be advised to take a fish oil supplement to replace heart-healthy fats that are missing from your PKU diet.

Which foods should you eat?

People with PKU vary in how much Phe they can safely eat. Ask your provider what’s right for you. To make sure you stay within your safe limits, you may need to carefully track your Phe and protein intake. Using an app or food list can help.

Many fruits and vegetables naturally contain very little Phe. You can eat them freely on a PKU diet. Fruits in this category include apples, bananas, berries, mango, peaches, and pineapple. Veggies in this category include cabbage, carrots, cucumber, lettuce, onions, and tomatoes.

Certain fruits and vegetables contain a bit more Phe. They may be part of your diet but pay attention to how much you eat. This includes some dried fruits, such as dried banana and mango. It also includes veggies such as asparagus, avocado, broccoli, kale, potatoes, and spinach.

Some dairy substitutes may have a place in your diet, depending on the type and brand you choose. Examples are vegan cheeses and almond, coconut, and rice milks.

Rice may fit into your diet in limited amounts. Starches that may be useful for cooking include cassava flour, arrowroot, sago, tapioca, and cornstarch.

There are also foods that are specially made for a low-protein diet. Examples include low-protein breads, flour mixes, pasta, and egg replacers. These foods can expand your menu options.

Which foods should you pass up?

Don’t have foods with a high Phe content. They include:

  • Animal-based protein foods such as meat, poultry, fish, and eggs

  • Plant-based protein foods such as beans, soy foods, nuts, and seeds

  • Dairy foods such as milk and cheese

  • Certain grains, including wheat, oats, rye, barley, and quinoa

Other items to skip include beer and gelatin. They contain a lot of Phe.

You should also steer clear of foods and drinks that contain aspartame. This is a common low-calorie sweetener that releases Phe when digested. It’s found in products such as diet sodas, flavored drink mixes, and energy drinks. These products are required to carry a warning on the label about the risk for people with PKU.

Tips for following this diet

Tempt your taste buds with herbs and spices. The amounts used in cooking are so small that they have no real effect on your Phe intake. But they can have a big impact on your enjoyment!

In place of traditional spaghetti, scoop out the strands from cooked spaghetti squash. Or use a spiralizer. This is a kitchen tool that can cut a variety of vegetables into long, noodle-like strands.

Suggestions for planning meals

  • For breakfast, have a bowl of puffed rice cereal moistened with nondairy creamer. Add a grapefruit half, banana, or small bowl of berries on the side.

  • For lunch, have a bowl of vegetable soup and low-protein bread.

  • For dinner, have a baked potato with green beans and carrots.

  • Every day, consume the special high-protein, Phe-free mixture recommended by your provider or dietitian.

  • For cooking resources, visit the National PKU Alliance website.

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