10 Foods to Avoid with Phenylketonuria

Phenylketonuria, also known as PKU, is a genetic condition whereby the body is unable to break down the amino acid phenylalanine. This amino acid then builds up in the blood and tissues and can lead to brain damage, neurological problems, hyperactivity, seizures, and developmental disabilities. For this reason, all infants are screened for PKU before leaving the hospital. Babies who are found to have PKU are placed on a special diet consisting of high protein, low phenylalanine formula. Once these children transition to solids, they are placed on a low-protein diet that avoids foods such as milk, poultry, and red meat. Adherence to a low protein diet from birth allows the majority of patients to develop normally and avoid the developmental delays associated with the condition.

Individuals with PKU have a very limited repertoire of foods that can be consumed. This makes it difficult to ensure that the individual receives appropriate calories, nutrients, vitamins, and minerals that are important for childhood growth and development. Adults with PKU also need to maintain appropriate levels of these for overall health. A registered nutritionist can be helpful in creating low-protein meal plans that meet other nutritional requirements. Healthcare professionals can also recommend protein supplements that provide vitamins, minerals, trace elements, and amino acids while avoiding phenylalanine.

The bulk of a phenylketonuria diet is comprised of fruits and vegetables, low-protein foods, small amounts of cereal-based foods, fat, and sugar. The amount of protein in one’s blood varies, so frequent blood tests are necessary to measure protein levels and adjust diets accordingly. Still, there are certain protein-rich foods that must always be avoided.

1. Milk

Avoiding milk begins at or shortly after birth. Regular infant formulas contain more phenylalanine than infants with phenylketonuria can tolerate and must be avoided. Breast milk does contain phenylalanine, but limited amounts can be offered under the close supervision of a registered dietician with experience in phenylketonuria management. Special formulas are available for older children and adults. Although these formulas should be consumed throughout the day rather than at one setting, they should be part of a well-rounded PKU diet.

Beyond infancy, all dairy products should be avoided throughout life on a phenylketonuria diet. This includes milk, yogurt, ice cream, butter, and pudding as well as foods made with milk, such as mashed potatoes or cream-based soups. Milk can be difficult to avoid as it is often a hidden ingredient in many foods, such as cakes, biscuits, and candies. Foods that are labeled non-dairy may still contain milk proteins that can be problematic for those on a PKU diet. Ingredients like casin, caseinates, hydrolysates, lactose, and lactoglobulin indicate the presence of milk proteins within a food. Foods that are labeled pareve or parve mean that the food contains no milk or milk products but does not necessarily mean the food is low in protein. Specialized milk substitutes are available that can be obtained through a dietician.