Aspartame is an artificial sweetener that is added to food and drinks instead of natural sugars. Aspartate is a methyl ester of a dipeptide containing the two amino acids, aspartate and phenylalanine.
Aspartame is metabolized in the body into its three constituents: aspartate, phenylalanine, and methanol. Methanol can be further broken down into formaldehyde and formic acid. Phenylalanine is a naurally occuring amino acid, but can be dangerous to individuals with phenylketonuria, an inherited disorder that renders phenylalanine metabolism inefficient. Because of this, foods sold in the US must contain a warning to phenylketonurics that phenylalanine is present.
Phenylalanine (shown below) is a precursor for tyrosine, which is in turn a precursor for the catecholamines, which include dopamine, norepinephrine, and epinephrine. Phenylalanine can cross the blood-brain barrier, and when ingested in large amounts, can cause problems with serotonin production.
Aspartate is a starting point for the biosynthesis of many amino acids. These amino acids include methionine, lysine, isoleucine, and threonine. Aspartate is also a metabolite of the urea cycle and gluconeogenesis. It can be used as an excitatory neurotransmitter in the brain as it stimulates NMDA receptors, similar to glutamate.