Phenylketonuria may not necessarily require a special diet in adulthood. It is the first genetic metabolic disorder that can be treated through dietary control. Natural foods all contain a certain amount of phenylalanine, so once children with phenylketonuria are diagnosed, they should stop their natural diet and instead be given a low-phenylalanine diet. Low-phenylalanine formula treatment should continue at least until the age of 12. When the concentration of phenylalanine in the blood is controlled at an ideal level, a gradual addition of natural foods can be made. Larger infants and children can add foods such as milk, porridge, noodles, and eggs. However, these added foods should still primarily be low in protein and low in phenylalanine.