Skip to content
NeBu

2026-05-27 · 7 min read

Is aspartame bad for you — does it cause cancer?

Aspartame (E951), found in Diet Coke and sugar-free products, was classified as a "possible carcinogen" by IARC in 2023 — yet WHO/JECFA left the safe daily limit unchanged the very same day. What does that contradiction actually mean? A transparent breakdown of hazard vs. risk, using EFSA, JECFA, and IARC sources.

  • aspartame
  • sweetener
  • e951
  • cancer
  • efsa
  • iarc

When you spot "E951" or "aspartame" on the back of a Diet Coke, a sugar-free chewing gum, or a "zero-calorie" dessert, a quiet question tends to surface: "Is this stuff going to give me cancer?" The headlines that broke in the summer of 2023 did nothing to ease that worry — a body linked to the World Health Organization declared aspartame a "possible carcinogen." But on the very same day, a different WHO-linked committee said: "We are not changing the safe daily limit."

That confusing contradiction cannot be resolved without grasping the single most important concept in modern food safety: hazard and risk are not the same thing. In this article we explain what aspartame is, why the two 2023 rulings look contradictory but are not, what they mean for everyday consumption, and who genuinely needs to pay attention.

What is aspartame?

Aspartame is an artificial sweetener that is roughly 200 times sweeter than sugar. Because so little of it is needed, it is virtually calorie-free. It is made up of two amino acids — aspartic acid and phenylalanine — and breaks down into those components during digestion.

You will most often encounter it in:

  • Diet and zero-sugar fizzy drinks (the most common source — think Diet Coke, Pepsi Max, Coke Zero)
  • Chewing gum and sugar-free sweets
  • "Light" or "zero sugar" yoghurts and desserts
  • Tabletop sweetener tablets and sachets
  • Some medicines and syrups

On labels it appears as E951 or by its full name, aspartame.

The two 2023 rulings — why they look contradictory

In July 2023, two separate assessments of aspartame were published on the same day, and at first glance they appear to contradict each other:

  1. IARC (International Agency for Research on Cancer) classified aspartame as Group 2B — "possibly carcinogenic to humans". The basis: limited evidence of an association with hepatocellular (liver) cancer.
  2. JECFA (the FAO/WHO Joint Expert Committee on Food Additives) left the Acceptable Daily Intake (ADI: 40 mg/kg body weight) unchanged, concluding that "there is no safety concern at current levels of consumption."

How can two conclusions from within the same organisational umbrella both be correct? The answer is that they are answering different questions.

The key concept: hazard is not risk

This distinction sits at the heart of the NeBu methodology, so it is worth spelling out:

  • IARC produces a "hazard" classification. Its question is: "Can this substance cause cancer under any circumstances, and how strong is the evidence?" IARC's groups (1, 2A, 2B, 3) measure the strength of the evidence — not how much exposure is needed to cause harm.
  • EFSA and JECFA assess "risk." Their question is: "At the doses people actually consume, does this substance cause harm, and what is the safe limit?"

This is why a substance can be IARC Group 2B ("possible hazard") while carrying no meaningful risk when consumed within the safe daily limit. Consider sunlight (UV radiation): it sits in IARC Group 1 — "definitely carcinogenic" — yet that does not mean you should never go outside. The dose and the level of exposure are what matter.

For perspective: processed meat and sunlight are both IARC Group 1 (definite carcinogen). Aspartame sits one rung lower at Group 2B. The classification reflects the strength of evidence, not the magnitude of risk.

How much is actually "a lot"?

Let's look at the numbers. EFSA's safe daily limit is 40 mg per kilogram of body weight. For a 70 kg adult, that works out to roughly 2,800 mg of aspartame per day.

A typical can of diet soda contains around 200–300 mg of aspartame. To reach the ADI, a 70 kg adult would need to drink 9 to 14 cans of diet soda every single day, consistently. Real-world consumption sits far below that for the vast majority of people.

What this means in practice: aspartame is not a substance to panic about, but if diet sodas are essentially your water supply — several litres a day — it is a fair question to ask yourself. Transparency means exactly this: neither unnecessary fear nor the breezy reassurance of "completely harmless, drink as much as you like."

Who genuinely needs to be careful: phenylketonuria

The one health warning around aspartame that is unambiguous and beyond dispute has nothing to do with cancer. It concerns a hereditary metabolic disorder: phenylketonuria (PKU).

Aspartame breaks down in the body to produce phenylalanine. People with PKU cannot metabolise phenylalanine; its build-up causes serious neurological harm. This is why, under EU Regulation 1333/2008 (and, in Türkiye, the Turkish Food Codex aligns with EU rules), any product containing aspartame must carry the warning "Contains a source of phenylalanine." For everyone who does not have PKU, this label is not a danger signal — it is information for a very specific group.

Aspartame instead of sugar — is that healthier?

"Should I switch from regular Coke to Diet Coke for my health?" is a question we hear a lot. The nuance here matters:

  • The link between high sugar intake and obesity, type-2 diabetes, and tooth decay is well established and well evidenced. In that sense, a sweetener can offer a real calorie advantage.
  • However, in 2023 WHO stated that it does not recommend long-term use of non-sugar sweeteners for weight control — the long-term benefit evidence is weak.
  • Additionally, the updated Nutri-Score 2023 algorithm applies an extra negative score to sweetener-containing (diet) drinks. "Sugar-free" alone does not make a drink green or healthy.

The healthiest drink is still water — that is the starting point for both Nutri-Score and NeBu.

How NeBu evaluates aspartame

When NeBu scores a product containing aspartame, it applies the hazard-is-not-risk discipline rigorously. Our goal is not to stamp "additive present = bad" — the way some scanning apps do — but to put the ingredient in its proper context:

  • We evaluate the product as a whole, not just whether a single ingredient is present.
  • We handle sweetener-containing drinks according to the Nutri-Score 2023 scientific framework, which addresses them specifically within their nutritional category.
  • Every health claim we make is backed by a verifiable source (EFSA, JECFA, IARC) — not rumour or algorithm-generated fear.

When you see aspartame on a product card in NeBu, it is designed not to frighten you but to show you context: how much, in what product, and for whom it actually matters.

Summary

  • Aspartame (E951) is an artificial sweetener roughly 200 times sweeter than sugar; it is most commonly found in diet drinks such as Diet Coke and Pepsi Max.
  • In 2023 IARC classified it as "possibly carcinogenic (Group 2B)", but JECFA left the safe limit (40 mg/kg body weight per day) unchanged — because one measures hazard, the other measures risk.
  • To exceed the EFSA ADI, a 70 kg adult would need to drink 9–14 cans of diet soda every day; ordinary consumption is far below that threshold.
  • The one clear, unambiguous warning is for people with phenylketonuria ("contains a source of phenylalanine").
  • Being sugar-free does not automatically make a drink healthy; water remains the best choice.

Sources

For the full detail of the NeBu methodology, take a look at our /methodology page.