Aspartame - Metabolism and Phenylketonuria

Metabolism and Phenylketonuria

Upon ingestion, aspartame breaks down into residual components, including aspartic acid, phenylalanine, methanol, in ratio of 4:5:1 by mass and further breakdown products including formaldehyde and formic acid, accumulation of the latter being suspected as the major cause of injury in methanol poisoning. Human studies show that formic acid is excreted faster than it is formed after ingestion of aspartate. In some fruit juices, higher concentrations of methanol can be found than the amount produced from aspartame in beverages.

High levels of the naturally-occurring essential amino acid phenylalanine are a health hazard to those born with phenylketonuria (PKU), a rare inherited disease that prevents phenylalanine from being properly metabolized. Since individuals with PKU must consider aspartame as an additional source of phenylalanine, foods containing aspartame sold in the United States must state "Phenylketonurics: Contains Phenylalanine" on their product labels.

In the UK, foods that contain aspartame are legally required by the country's Food Standards Agency to list the substance among the product's ingredients and carry the warning "Contains a source of phenylalanine" – this is usually at the foot of the list of ingredients. Manufacturers are also required to print '"with sweetener(s)" on the label close to the main product name' on foods that contain "sweeteners such as aspartame" or "with sugar and sweetener(s)" on "foods that contain both sugar and sweetener".

In Canada, foods that contain aspartame are legally required by the country to list the substance among the product's ingredients and include a measure of the amount of aspartame per serving. As well, labels must state that the product contains phenylalanine – this is usually in the order of ingredients, contained in brackets.