@Incal phenylalanine and aspartic acid are both naturally occurring amino acids in the body and would exist within the body with or without the intake of aspartame. And your breakdown sequence is backwards, it first breaks down into methanol and THEN into formaldehyde and formic acid. But those amines in natural proteins also break down when proteins are recycled. Additionally, you get some methanol fruits and vegetables. The body has natural pathways to detoxify formaldehyde, converting it to formic acid and eliminating it.