In phenylketonuria, which dietary modification is essential?

• A. High phenylalanine diet
• B. No restriction
• C. High carbohydrate diet
• D. Low phenylalanine diet

Answer: (D)

Phenylketonuria is caused by a deficiency of the enzyme that converts phenylalanine to tyrosine, so phenylalanine accumulates and can damage brain development. The essential dietary modification is a diet very low in phenylalanine, using specialized formulas that supply all other amino acids while limiting phenylalanine intake. Tyrosine becomes essential and is often provided through the diet or formula. This approach prevents toxic buildup and supports normal neurodevelopment. It’s also important to avoid foods and additives high in phenylalanine, such as aspartame. In short, restricting phenylalanine intake is the key management strategy to prevent intellectual disability and other neurologic problems associated with PKU.