Aspartame
Aspartame is the most argued-over sweetener: in 2023 the World Health Organization's (WHO's) cancer agency called it "possibly carcinogenic" on the same day another WHO committee confirmed its safe daily limit. Both were right about different things — the label describes a possible hazard, not a measured risk — and the more useful worry is the population data linking it to diabetes, which still can't show cause and effect.
At normal intake, the "possibly carcinogenic" label is a hazard rating, not a measured risk, and the population signal for cancer is unproven. The better reason to cut back is the same as for every diet sweetener: use diet drinks to get off sugar, then move towards water, coffee and tea.
What it is
Aspartame is an intense, calorie-free sweetener used in diet soft drinks and, less obviously, in chewing gum, yogurt, breakfast cereal, toothpaste and cough drops. It is one of the four sweeteners — with acesulfame-K, sucralose and saccharin — that were licensed on the assumption that anything calorie-free couldn't matter metabolically.
"Possibly carcinogenic", explained
In July 2023 two WHO bodies issued what looked like opposite verdicts on the same day. The International Agency for Research on Cancer (IARC) classed aspartame as "possibly carcinogenic to humans" (Group 2B) on limited evidence for liver cancer. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) kept the acceptable daily intake at 40 mg per kilogram of body weight, calling the evidence of a cancer link in humans "not convincing".[1]
The two don't conflict. IARC's groups say how confident the agency is that something can cause cancer, not how much cancer it causes at the doses people meet. Group 2B also holds pickled vegetables and whole-leaf aloe vera extract. IARC published the full assessment in 2024, unchanged.
By JECFA's own example, a 70-kg adult would need more than 9–14 cans of diet soda a day to exceed the limit — assuming no aspartame from anything else, which is unrealistic given how many products contain it.
What the population studies show
The biggest numbers come from a large French study that recorded everything people ate, brand by brand (NutriNet-Santé).
- Cancer: higher aspartame consumers had about 15% more cancer than non-consumers, and about 22% more breast cancer.[2]
- Type 2 diabetes: aspartame carried about 1.6 times the risk and acesulfame-K about 1.7 times, more than sucralose did.[3]
- Heart and stroke: across all artificial sweeteners, about 9% more cardiovascular disease, driven mainly by strokes.[4]
Read these as the top of the range. The cohort is mostly women and unusually health-conscious, and people developing metabolic disease may switch to diet products because of it. Pooled analyses across millions of people put the diabetes link for sweeteners as a group nearer 14–26%, and WHO's own review found no link with cancer overall. The details, and why the stroke signal holds up better than most, are on Sugar substitutes.
What it does inside you
In a two-week trial of 120 healthy adults, in which some took one of four sweeteners below the official limits, aspartame changed the bacteria in the gut and mouth and the chemicals circulating in the blood. It was not one of the two — saccharin and sucralose — that worsened blood-sugar responses within those two weeks.[5]
In mice and monkeys, aspartame set off an insulin release through the vagus nerve that inflamed artery walls and sped up plaque.[6] That is a reason to keep looking, not a finding about people.
The official limits
| Body | Acceptable daily intake (per kg body weight) |
|---|---|
| JECFA and the European Food Safety Authority (EFSA) | 40 mg |
| US Food and Drug Administration (FDA) | 50 mg |
EFSA reconfirmed 40 mg in 2026 while re-evaluating the aspartame-acesulfame salt used in some products, finding no new studies that would move the limit and no age group exceeding it.[7] These limits are ceilings, not targets.
What to do
- Don't panic about a diet soda on cancer grounds. The label is a hazard classification, and intake surveys sit below the limit.
- Swap sugary drinks for diet ones if that's the step you can make — it beats sugar.
- Then aim for water, coffee or tea as the default, because the long-term population data, though unproven, all lean the same way.
- If you want a sweetener you add yourself, stevia has the more reassuring record.
Further reading
- WHO / IARC / JECFA. Aspartame hazard and risk assessment results released. 2023.[8]
- Debras C et al. Artificial sweeteners and cancer risk: results from the NutriNet-Santé population-based cohort study. PLOS Medicine 2022.[9]
- Debras C et al. Artificial sweeteners and risk of type 2 diabetes in the prospective NutriNet-Santé cohort. Diabetes Care 2023.[10]
- Suez J et al. Personalized microbiome-driven effects of non-nutritive sweeteners on human glucose tolerance. Cell 2022.[11]