Aspartame

Aspartame (E951) is a dipeptide methyl ester sweetener — L-aspartyl-L-phenylalanine methyl ester — approximately 200 times sweeter than sucrose at low concentrations, with a clean, sugar-like taste profile that has made it the dominant high-intensity sweetener in tabletop applications and diet carbonated beverages since its commercial approval in the 1980s. It is metabolised completely by intestinal esterases to aspartic acid, phenylalanine, and methanol — compounds that are normal constituents of fruits, vegetables, and dietary proteins. As a peptide, aspartame provides 4 kcal/g, but because the usage concentration is 1/200th that of sucrose, its caloric contribution to food is negligible. It is heat-labile and loses sweetness during prolonged cooking, limiting its use to post-processing addition or heat-stable blends.

JECFA established an ADI of 40 mg/kg body weight per day for aspartame (evaluated 1980, 1983, 2023). The 2023 JECFA evaluation was prompted by new mechanistic data on carcinogenicity and represented the most comprehensive review to date. IARC simultaneously classified aspartame as Group 2B (possibly carcinogenic to humans), based primarily on limited epidemiological associations in three prospective cohort studies and mechanistic data from rodent studies; JECFA maintained the 40 mg/kg ADI, concluding the evidence was not sufficient to change the safety determination at this ADI level. This IARC/JECFA divergence — a joint announcement that created public confusion — reflects the organisations' different mandates: IARC assesses hazard (can it cause cancer at any dose?) while JECFA assesses risk (is it dangerous at food use levels?).

Aspartame is authorised under EU Regulation (EC) No 1333/2008 and FDA 21 CFR §172.804. Critically, all aspartame-containing foods must carry the mandatory declaration "contains a source of phenylalanine" to protect individuals with phenylketonuria (PKU), who cannot metabolise phenylalanine and for whom aspartame-derived phenylalanine represents a clinically significant dietary hazard. For the non-PKU population, aspartame's safety at food use levels has been consistently confirmed by regulatory bodies worldwide for over 40 years, notwithstanding the 2023 IARC Group 2B classification.