This is one type of sugar substitute. It is made up of the amino acids phenylalanine (Phe) and aspartic acid (Asp). It is sold under the brand names “Equal,” “Nutrasweet,” “Sweetmate” and “Canderal.” Aspartame is harmful for people with PKU because it causes Phe to build up in the blood. High levels of Phe can cause health problems and brain damage. It is important for people with PKU to avoid any foods or drinks that contain aspartame.