Children with phenylketonuria should not eat meat and should try to eat as little as possible. Phenylketonuria is caused by a defect in the phenylalanine hydroxylase enzyme in the phenylalanine metabolic pathway, which results in a metabolic disorder of phenylalanine in the liver. Phenylketonuria is the first hereditary metabolic disease that can be treated by dietary control. All natural foods contain a certain amount of phenylalanine. Once diagnosed, children should stop consuming a natural diet and be given a low-phenylalanine diet for treatment. Meat is rich in protein and also contains a high amount of phenylalanine, thus the intake of meat must be restricted or minimized.