Aspartame contains Phenylalanine. PKU is a genetic defect that causes Phenylalanine to build up in their system. people with pku need to be on a low protein diet with no aspartame because it'll cause build up in their bodies and can cause intellectual disabilities
It also can be due to depression. people ends up having a hard time and they just don't know what else to do. they end up taking the wrong path and try to hide this pain