Aspartame is a sweetener that is widely used in food production and processing. In GB 2760-2014 National Standard for Food Safety Standard for the Use of Food Additives, there is a special requirement for the labeling of aspartame, that is, it must be labeled as: aspartame (containing phenylalanine).

Why must aspartame be labeled as: aspartame (containing phenylalanine)?

Aspartame is broken down into phenylalanine, aspartic acid and methanol by enzymes in the gastrointestinal tract of the human body. Even if a large amount of aspartame is ingested (200 mg/kg body weight), aspartame cannot be detected in the blood.
The reason why foods with aspartame are required to be labeled as “contains phenylalanine” is that patients with a genetic disorder called phenylketonuria are born with a deficiency of an enzyme that results in an impaired metabolism of phenylalanine, which prevents phenylalanine from being converted to tyrosine.
If such patients consume food containing phenylalanine, it will bring greater health risks to such patients. Therefore, in order to remind patients with phenylketonuria, special requirements have been imposed on aspartame, that is, food products with aspartame added must be labeled as follows in the ingredient list: aspartame (containing phenylalanine).