Today, scientists know what foods have phenylalanine in them, and they have created a special diet for people with PKU. Since they cannot use it, people with PKU cannot eat foods that have a lot of phenylalanine, like eggs, meat and milk. An artificial sweetener called aspartame is also a source of phenylalanine. People with PKU take a lot of vitamins to make up for the foods they cannot eat, especially vitamins B6 and B12.