Unlock the Ultimate PKU Diet Food List: Your Complete Guide to Managing Phenylketonuria with Ease!

Phenylketonuria (PKU) is an autosomal, recessive, genetic disorder that requires a strict, lifelong low phenylalanine diet. This diet aims to reduce Phe intake while maintaining good overall nutrition. The following guide provides detailed information about the PKU diet, including which foods to eat, which to avoid, and tips for successful meal planning.

Understanding PKU and the Importance of Diet

Phenylketonuria (PKU) is a condition where a genetic mutation causes low levels or an absence of an enzyme called phenylalanine hydroxylase (PAH). It is caused by a deficiency of the enzyme phenylalanine hydroxylase which normally converts phenylalanine to tyrosine. PAH is normally involved in breaking down the amino acid phenylalanine (Phe).

In people with PKU, Phe accumulates in the body. Because Phe is toxic to brain tissue, children born with PKU can develop intellectual disability if PKU treatment isn’t started shortly after birth. The main treatment for PKU is a special diet. Following a low-phenylalanine diet can prevent intellectual disability and other complications in people with phenylketonuria.

The Core Principles of the PKU Diet

The PKU diet is a special diet that’s maintained throughout your lifetime. The goals of the PKU diet are:

Restricting natural intake of Phe: Amino acids are the building blocks of proteins, so Phe is found in protein sources. Due to this, people with PKU must follow a low protein diet.
Using a protein substitute: While the PKU diet aims to limit Phe intake, it’s still vital that people with PKU get other amino acids from their diet.

To ensure this, you may need to take vitamins and mineral supplements or add them to the protein substitute formula.

Read also: Foods for Pre-Diabetes

The PKU Diet "Target"

This target is an easy way to visualize the foods allowed on the diet for PKU. The phenylalanine-free formula, such as Phenyl-Free*, is the center of the target diet. As the foods get further away from the bull's-eye, they are higher in phenylalanine. The foods outside the target are not included in the low-phenylalanine meal plan.

Foods to Include in the PKU Diet

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. The types of foods that people with PKU can eat include:

Most Fruits and Vegetables: 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. Although all fruits and vegetables containing phenylalanine ≤75 mg/100 g contribute a small amount of daily phenylalanine, this is generally not enough to affect blood phenylalanine control.
Sugars: Honey, jams, and syrups.
Fats: Butter, margarine, and vegetable oil.
Low Protein Starches: Cornstarch, tapioca, and arrowroot.
Herbs and Spices: 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!
Drinks: Coffee, green or black tea, and fruit juice.
Certain Dairy Substitutes: 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. Any vegan cheese that contains protein ≤ 0.5 g/100 g (or ≤ 25 mg phenylalanine/100 g) can be given in the diet without calculating the phenylalanine/protein content.
Rice: Rice may fit into your diet in limited amounts.
Starches for Cooking: Starches that may be useful for cooking include cassava flour, arrowroot, sago, tapioca, and cornstarch.
Low-Protein Foods: There are also foods that are specially made for a low-protein diet. Examples include low-protein breads, flour mixes, pasta, and egg replacers. A selection of low protein breads, flour mixes, pizza bases, pasta, biscuits, and egg replacers, are available. These foods can expand your menu options. Low protein special products are allocated in the diet without restriction if all ingredients are exchange-free e.g. food starch and oil. Although there is a wide range of ‘starch based’ specially manufactured low protein foods such as bread, flour, pasta and biscuits available, patients have variable access to these across Europe. They are generally expensive if not government/insurance funded or supplied by the hospitals. They may provide up to 50% of energy intake.

Foods to Eat in Moderation

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. Potatoes are an exception (see Phenylalanine allocation in the diet section).

Foods to Avoid on the PKU Diet

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

Animal-Based Protein Foods: Meat, poultry, fish, and eggs.
Plant-Based Protein Foods: Beans, soy foods, nuts, and seeds.
Dairy Foods: Milk and cheese.
Certain Grains: Wheat, oats, rye, barley, and quinoa.
Other Items: Beer and gelatin. They contain a lot of Phe.
Aspartame: 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. Aspartame (E951) is an artificial sweetener and 56% is converted to free phenylalanine and so should be excluded in a low phenylalanine diet. It is added to soft drinks, chewing gums, sweets, desserts, jelly and tabletop sweeteners. Although aspartame should always be included on food labels, the amount of phenylalanine it provides remains undisclosed.

The Role of Phenylalanine-Free Formula

The phenylalanine-free formula is the most important part of the diet for PKU. Research has shown that this diet should be followed for life. Keeping blood phe levels in the safe range helps to prevent problems with thinking and problem solving. A special phenylalanine-free formula, such as Phenyl-Free*, contains protein, vitamins, minerals and energy (calories) with no phenylalanine. With formula, a person with PKU gets plenty of protein, without the side effects of the high phe content of most foods.

Read also: Shopping for Raw Foods

Types of Protein Substitutes

Powdered weaning (thickened) amino acids without phenylalanine.
Powdered amino acid supplements (with or without the addition of vitamins, minerals, long chain fatty acids, carbohydrate and fat), reconstituted with water and made into semi-solid (spoonable) consistency or drink.
Ready to use liquid protein substitutes (usually with the addition of vitamins, minerals, long chain fatty acids, carbohydrate and fat).
Tablets or capsules containing amino acids without phenylalanine ±vitamins and minerals.
Snack bars containing amino acids without phenylalanine. They are usually given in combination with other protein substitutes to make up requirements and aid variety.

Protein substitutes based on amino acids have a high osmolality. Osmolality is the concentration of a solution expressed as the total number of solute particles per kilogram. Products with a high osmolality may lead to delayed gastric emptying and cause diarrhoea. When water is added to a powdered protein substitute, the tyrosine is hydrophobic and forms an insoluble layer at the top of the solution making the product less acceptable. Ideally, all protein substitutes should be prepared immediately prior to use. It is essential that protein substitute supplies are carefully rotated within the home and stored according to manufacturer’s instructions.

Calculating Phenylalanine Intake

All individuals with PKU should be allocated a daily allowance of phenylalanine according to their individual tolerance. This enables individuals to maintain a consistent phenylalanine/protein intake. There are different ways of calculating phenylalanine/protein intake and there is little evidence to show that any method is better than another. Phenylalanine/protein intake may be calculated by daily grams of protein or milligrams of phenylalanine. Throughout Europe, health professionals may use one of five systems to calculate the amount of phenylalanine eaten each day and all systems achieve acceptable blood phenylalanine control. In all systems, fruits and vegetables except those containing phenylalanine ≥75 mg/100 g can be given without estimating their individual phenylalanine content. This means they are not calculated as part of the daily phenylalanine analysis.

Phenylalanine Exchange System

For regular manufactured foods e.g. sauces, breakfast cereals, their protein food labelling is used to determine if they are suitable for a low phenylalanine diet. This can be challenging as sometimes protein labelling is confusing.

In dry foods, protein content may be listed only after a food has been ‘theoretically’ reconstituted.
Manufacturers may assume that some food items are reconstituted with cow’s milk e.g. desserts or custards and this is the protein value that may be stated on the label.

Tips for Following the PKU Diet

Monitor Phe Levels Regularly: If you have PKU, your doctor will regularly monitor the levels of Phe in your blood. This involves collecting a small sample of blood from your finger and placing it on a special card. The card is then sent to a lab to be analyzed.
Work with a Dietitian: A dietitian will work with you to develop a PKU diet plan that meets your specific needs. They may adjust this plan periodically. For example, the Phe levels in your blood and your nutritional needs may change during growth spurts.
Track Phe and Protein Intake: 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.
Read Food Labels Carefully: Always check food labels for phenylalanine content and hidden sources of protein or aspartame.
Plan Meals in Advance: Plan your meals and snacks ahead of time to ensure you have access to appropriate foods.
Get Creative with Cooking: Use low-protein ingredients and herbs and spices to create flavorful and satisfying meals.
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.

Sample Meal Plans

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.

Managing High Blood Phenylalanine Levels

No studies have been conducted to give an indication of how much dietary change is needed when blood phenylalanine levels have been consistently above target range for many years. The degree of change necessary may vary from individual to individual and will also be influenced by the presence of catabolism, growth and pregnancy. It may be that for some patients, strict adherence with the existing dietary prescription is enough to achieve the European PKU Guidelines target ranges.

Carefully document all intake of food, drink and protein substitute.
If a patient is eating an unrestricted diet (i.e. meat, fish and eggs), it may be enough to remove some or all high protein foods from the diet and supplement with a suitable protein substitute to bring blood phenylalanine to within target range.
If blood phenylalanine levels remain higher than the target ranges, the next stage is to gradually decrease the dietary phenylalanine by 50 mg/day (equivalent to 1 g protein) at each diet adjustment. If after 3 consecutive blood spots, phenylalanine levels are not within target range, repeat this step and reduce dietary intake by a further 50 mg/day (protein, 1 g/day), until blood phenylalanine levels are within target range. Dietary phenylalanine intake should not be reduced to less than a minimum of 150 mg/day in children under regular conditions [5].

During any dietary change it is important to monitor blood phenylalanine levels regularly. Giving adequate energy intake from very low protein sources is essential to meet energy requirements and to minimise h catabolism that can lead to poor blood phenylalanine control.

Addressing Low Blood Phenylalanine Levels

During illness poor appetite and low energy intake are common, and high blood phenylalanine concentrations occur due to catabolism (protein breakdown). There is little work defining the best management for illness in PKU, but the guidelines in Table 8 may be helpful. Protein substitute given when there is a high temperature may lead to vomiting. If on dietary treatment only, there is no need …

Repeat blood phenylalanine level, and if is still low, consider an increase of natural protein by approx.
Infants may take phenylalanine- reduce gap free infant protein substitute overnight, which may lower morning blood concentrations.
Consider increasing natural protein by approx.

Special Considerations

Pregnancy

The PKU diet is especially important during pregnancy. High Phe levels in the mother's blood can harm the developing fetus. Women with PKU who are planning to become pregnant should work closely with their doctor and dietitian to optimize their diet and Phe levels before conception.

Illness

During illness, poor appetite and low energy intake are common, leading to catabolism (protein breakdown) and high blood phenylalanine concentrations. Consult with your healthcare provider for guidance on managing the PKU diet during illness.

Dental Health

There are few studies that report the prevalence of dental caries in PKU with results of studies contradictory. There are certainly conflicting objectives in PKU care, i.e. Juices or sugary drinks should not be added to infant bottles; protein substitutes should not be added to infant bottles > 1 year of age. Sweet foods and juices are better confined to mealtimes only. Avoid using dummies/pacifiers from 12 months of age.

Check understanding/calculation of phenylalanine allowance/ exchanges, misinterpretation/misunderstandings of protein amounts in foods.
Check any intentional dietary non-adherence (e.g.
Check adherence (at home, nursery, school).
Increase energy intake/give extra carbohydrate.
If blood phenylalanine levels are consistently high, consider a reduction in natural protein/phenylalanine by approx.

The European PKU Guidelines

In 2017 the first European PKU Guidelines were published. These guidelines contained evidence based and/or expert opinion recommendations regarding diagnosis, treatment and care for patients with PKU of all ages. This diet manual describes the practical application of the European PKU guidelines [1].

The European PKU Guidelines recommend that the total protein intake should supply 40% more than the FAO/WHO/UNU safe levels of protein intake [1]. However, this amount is arbitrary and unconfirmed by research. As most of the available protein substitutes are derived completely from phenylalanine-free amino acid sources, it is recommended that a dose higher than the FAO/WHO/UNU is given. This extra amount compensates for the ineffective absorption of natural/intact protein (which is mainly plant based), poor utilisation of L-amino acids and sub-optimal energy intake [12, 13].

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