All other people are able to metabolise and eliminate excess phenylalanine without problem. The peak, or maximum, changes were higher in subjects who were heterozygous for PKU but, even for these people, the changes were similar to the normal rises seen after consuming a meal. Further reassurance comes from consideration of the amount of phenylalanine released by digestion of aspartame, compared with that available from other foods. Aspartame is only a minor source of dietary phenylalanine. The typical adult intake of phenylalanine from all sources is 3 to 5g per day.
Aspartic acid is another normal neurotransmitter within the brain.
As we have already seen, anything taken to excess can be toxic, and that is also true for aspartic acid. Methanol, or methyl alcohol, is naturally found in fruits and vegetables. It occurs both as the free alcohol and bound in the form of compounds called methyl esters. Pectin is an example of a food component which contains methyl ester groups and which is present in all fruits and vegetables. Methanol is released when such esters are digested.