ALSOFOUNDINAspartame (NutraSweet)
IARC Group 2BWHO calls it a 'possible carcinogen.' The FDA disagrees. Also listed on labels as E951, NutraSweet, Equal.
E-number: E951
What it is
An artificial sweetener about 200 times sweeter than sugar, built from two amino acids. It was discovered by accident in 1965 when a chemist licked his finger, became NutraSweet and Equal, and has been the backbone of the diet-soda industry since the 1980s.
Why it's in food
It delivers sugar-level sweetness for almost zero calories and tastes cleaner than older sweeteners like saccharin. One catch decides where it shows up: heat breaks it down, so it lives in sodas, yogurts, and gum — and almost never in anything baked.
US vs EU status
United States
FDA-approved since 1981 and, in the agency's words, one of the most-studied additives in the food supply, with a daily limit of 50 mg per kilogram of body weight. When the WHO's cancer agency flagged it in 2023, the FDA publicly disagreed and changed nothing. Every product containing it must carry a phenylalanine notice for people with PKU.
European Union
Permitted as E951 with a slightly stricter daily limit of 40 mg/kg, reaffirmed by Europe's food safety authority in 2013. The real drama came in July 2023, when the WHO split with itself: its cancer arm (IARC) classified aspartame as 'possibly carcinogenic to humans' the same week its additives committee reviewed the evidence and left the daily limit untouched.
Common products
- Most diet sodas, including Diet Coke and Coke Zero
- Sugar-free chewing gum
- Light and sugar-free yogurts
- Sugar-free gelatin and pudding cups
- Equal and NutraSweet tabletop packets
- Powdered drink mixes and children's chewable medicines
Cleaner swaps
- Stevia leaf extract
- Monk fruit extract
- Allulose
- Smaller amounts of real sugar or honey
Case note
One week in July 2023, one WHO agency called aspartame a possible carcinogen while another WHO committee said your daily limit hadn't changed. Same molecule, same studies, same organization — two answers. When the referees split the call, the can in your hand won't tell you. The file has to.
Read the full investigation: Is Aspartame Safe? What the Cancer Research Actually Says →
FAQ
Does aspartame cause cancer?
Contested. In July 2023 the WHO's cancer agency (IARC) put aspartame in Group 2B — 'possibly carcinogenic to humans' — a category based on limited evidence that also includes things like pickled vegetables and aloe vera extract. The same week, the WHO's own additives committee reviewed the data and kept the acceptable daily intake unchanged, and the FDA publicly disagreed with the classification. Possible is not proven — but it is the first crack in a 40-year 'fully safe' story.
How much aspartame is considered safe per day?
The WHO and EU set the limit at 40 mg per kilogram of body weight per day; the FDA allows 50. For a 150-pound adult, the stricter limit works out to roughly a dozen or more cans of diet soda every single day, for life. Typical consumers come nowhere near it — the debate is about whether the limit itself measures the right risks.
Why do labels warn about phenylalanine?
Aspartame breaks down into phenylalanine, an amino acid that people with the rare genetic condition PKU (phenylketonuria) cannot process. For them the warning is serious and mandatory in both the US and EU. For everyone else, that line on the can isn't the safety debate — the cancer question is.
Is aspartame banned anywhere?
No major market bans it — it's legal in the US, EU, UK, Canada, and beyond, all with similar daily limits. Unlike Red 40, there's no warning label fight here; the fight is between scientific bodies reading the same studies and reaching different levels of comfort.
How the FDA decides what reaches your table and your medicine cabinet — and how it learned to decide.
Related files
Sucralose Splenda
600× sweeter than sugar. Gut-microbiome questions still open.
Open file →Acesulfame K Acesulfame potassium
Almost always blended — so you never taste it working.
Open file →Saccharin Sweet'N Low
Once carried a US cancer warning. Quietly un-warned in 2000.
Open file →High-Fructose Corn Syrup HFCS
'Generally recognized as safe' since the '80s. The debate never ended.
Open file →