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Are artificial sweeteners worse than sugar?

What you hear: “Diet sweeteners like aspartame are worse for you than sugar and cause cancer.”

What the studies found

In 2023 the WHO cancer agency labelled aspartame 'possibly carcinogenic' (Group 2B) based on limited evidence, while the WHO/FAO food additive committee kept the safe daily limit at 40 mg per kg of body weight, which a 70 kg adult would only pass at more than 9 to 14 cans of diet soda a day. Separately, WHO advised against using sweeteners for weight control, because the evidence shows no long-term benefit for body fat, and observational studies hint at higher diabetes and heart risk that may be due to other factors. One 2023 study linked the highest blood erythritol levels with roughly 1.8 to 2.2 times the risk of heart attack, stroke or death in people already having heart checks, and found erythritol made platelets stickier in lab tests; this is an observed link, not proof. There is no good evidence that sweeteners are worse than the sugar they replace.

Take care: People with phenylketonuria must avoid aspartame. Given the erythritol findings, people with heart disease may prefer not to rely heavily on erythritol-sweetened products until more is known.

What you could do

Diet drinks are a reasonable step down from sugary ones, but water, unsweetened tea or coffee are the better long-term habit.

See it in the habit library, with what it means for your own longevity score.

Not medical advice. General information from published studies, not a diagnosis or a treatment plan. Talk with your doctor before starting a supplement or changing a medicine, especially if you are pregnant, take other medicines or have a health condition.

How we judged it

Partly true: Some truth, but oversold as usually said. We judge the claim as it is usually said online, not the habit itself. Trials assign people at random, so they can show cause; observed studies follow people and show a link, not proof. Last checked: October 2026.

The studies, in their own words

1. WHO, IARC and JECFA joint news release 2023

   Citing “limited evidence” for carcinogenicity in humans, IARC classified aspartame as possibly carcinogenic to humans (IARC Group 2B) and JECFA reaffirmed the acceptable daily intake of 40 mg/kg body weight.

2. WHO, IARC and JECFA joint news release 2023

   For example, with a can of diet soft drink containing 200 or 300 mg of aspartame, an adult weighing 70kg would need to consume more than 9–14 cans per day to exceed the acceptable daily intake, assuming no other

3. WHO news release on non-sugar sweetener guideline 2023

   The recommendation is based on the findings of a systematic review of the available evidence which suggests that use of NSS does not confer any long-term benefit in reducing body fat in adults or children.

4. WHO news release on non-sugar sweetener guideline 2023

   Because the link observed in the evidence between NSS and disease outcomes might be confounded by baseline characteristics of study participants and complicated patterns of NSS use, the recommendation has been assessed as conditional

5. Witkowski et al. Nat Med 2023

   confirmed this association (fourth versus first quartile adjusted hazard ratio (95% confidence interval), 1.80 (1.18-2.77) and 2.21 (1.20-4.07), respectively).

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