In PKU, why is tyrosine supplementation often included in the diet?

• A. To provide tyrosine that becomes essential due to phenylalanine restriction
• B. To supply essential fatty acids
• C. To increase phenylalanine levels
• D. To reduce tyrosine levels

Answer: (A)

In PKU, tyrosine supplementation is included because phenylalanine hydroxylase deficiency prevents the body from converting phenylalanine to tyrosine, making tyrosine an essential amino acid that must be supplied from the diet. With phenylalanine restricted to prevent buildup, there isn’t enough phenylalanine available to supply tyrosine endogenously, so adding tyrosine supports protein synthesis and the production of important downstream compounds. The other options don’t fit: supplementation isn’t for essential fatty acids, it’s not intended to raise phenylalanine levels, and it doesn’t aim to lower tyrosine.