E951 — Aspartame
E951 (Aspartame), a sweetener, is rated "avoid": worth avoiding. A low-calorie sweetener in diet sodas and sugar-free products. In 2023 the WHO's cancer agency (IARC) classified it as possibly carcinogenic to humans, while the WHO's own additives committee reviewed the same evidence and kept its daily limit unchanged. Two arms of the same body disagree.
What is Aspartame?
A lab-made sweetener roughly 200 times sweeter than sugar, built from two amino acids. Common in diet sodas, sugar-free gum, light yogurts, tabletop sweeteners, and protein bars.
What does it do to the body?
In your gut it breaks down into aspartic acid, phenylalanine, and a small amount of methanol. The cancer signal IARC acted on is limited human evidence for liver cancer from a handful of studies it judged too flawed to be conclusive — a flag for more research, not a demonstrated risk. Reaching the daily limit takes roughly 9 to 14 cans of diet drink a day for a 70 kg adult, so heavy daily users are the group with any real exposure question. People with the rare genetic condition phenylketonuria must avoid it entirely.
What regulators say
This is a genuine split. In July 2023 IARC classified aspartame as Group 2B, 'possibly carcinogenic to humans' — a hazard label meaning the evidence is limited, sitting alongside things like aloe vera extract. The same week, JECFA (the WHO/FAO additives committee) reviewed the evidence, called the cancer association unconvincing, and reaffirmed the acceptable daily intake of 40 mg per kg of body weight per day. EFSA holds the same 40 mg limit and the FDA allows 50 mg. Separately, WHO's 2023 guideline advises against using sweeteners for weight control.
Risk rating: Avoid
Known or suspected to cause harm: a substance EFSA or another regulator has flagged, or one restricted in some jurisdictions. Best kept out of a regular diet.
Source: WHO / IARC / JECFA — aspartame hazard and risk assessment (July 2023) ↗