Aspartame and Cancer: What IARC's Review Means

On July 14, 2023, two bodies published findings on aspartame at once. That timing is why the news coverage got confusing.

IARC is the World Health Organization's cancer research agency. It classified aspartame as possibly carcinogenic to humans, Group 2B.

JECFA is the Joint FAO/WHO Expert Committee on Food Additives. It kept the acceptable daily intake at 40 mg per kilogram of body weight.

Both read the same studies. They did not disagree. They were answering two different questions. That difference is the whole story here.

Aspartame is an artificial sweetener, in use since the 1980s. It is a dipeptide. That means it is built from two amino acids: phenylalanine and aspartic acid. Both turn up naturally in protein foods.

It is about 200 times sweeter than table sugar, so very little is needed. It is also not heat stable. It loses its sweetness when heated. That is why it is rarely used in baked goods.

WHO's list of products holding it is longer than most people expect. It covers diet drinks, chewing gum, gelatin, ice cream, yogurt and other dairy, breakfast cereal, toothpaste, and medicines such as cough drops and chewable vitamins.

IARC's label rested on three separate findings of limited evidence:

• Limited evidence in humans. The cancer was hepatocellular carcinoma, a type of liver cancer.
• Limited evidence in lab animals.
• Limited evidence on how cancer might be caused.

That was IARC's first ever review of aspartame. Mary Schubauer-Berigan of the IARC Monographs programme framed it as a call for research. Limited evidence in all three areas, she said, shows how much more work is needed.

Two points about Group 2B are worth keeping. It is the third of four levels, not the top. And it is used in one of two cases. Either human evidence is limited but not convincing, or animal evidence is convincing. Not both.

IARC is also blunt about what its labels do not do. They show how strong the evidence is that something can cause cancer. They say nothing about the risk at any real exposure level. Our explainer on hazard versus risk unpacks that split.

JECFA read the same data and asked a different question. How likely is harm at the amounts people really consume?

Its answer was short. The data gave no reason to change the existing acceptable daily intake of 0 to 40 mg per kilogram of body weight. This was JECFA's third review of aspartame. Moez Sanaa of WHO summed up the reading. The evidence of a link between aspartame and cancer in humans is not convincing.

Francesco Branca directs WHO's Department of Nutrition and Food Safety. He put both findings in one line. Safety is not a major concern at the doses commonly used. But possible effects have been described, and they need more and better studies.

This is the part that turns a label into something usable.

Start with JECFA's own example. A can of diet soft drink holds 200 or 300 mg of aspartame. Take an adult weighing 70 kg, about 154 pounds. That person would have to drink more than 9 to 14 cans in a day to pass the 40 mg limit. That assumes no aspartame from any other food.

The FDA runs its arithmetic on packets instead. Its limit is 50 mg per kilogram. A 60 kg person, about 132 pounds, would need 75 tabletop sweetener packets in one day to reach it.

The FDA's limits for other sweeteners are far lower. Acesulfame potassium and saccharin sit at 15 mg per kilogram. Sucralose sits at 5. Neotame sits at 0.3. Aspartame's higher figure reflects its safety data, not looser review.

The FDA's limit is 50 mg per kilogram per day, not 40. Both numbers are real. They come from different reviews.

The FDA has regulated aspartame as a food additive since 1974. The first approval covered tabletop use, chewing gum, cold cereals, and dry mixes for products such as drinks, gelatins, and puddings. It became a general-purpose sweetener in 1996. The agency says it has reviewed more than 100 studies. Those covered cancer, metabolism, and effects on the reproductive and nervous systems.

The FDA also disagreed in public with IARC's basis. It says it reviewed the material in IARC's 2021 review when it first appeared. It then identified significant shortcomings in the studies IARC relied on. The FDA states it has no safety concerns when aspartame is used under approved conditions.

This has nothing to do with cancer. People with phenylketonuria, or PKU, must avoid aspartame. PKU is a rare inherited disorder. It makes phenylalanine hard to process, and buildup can harm the brain.

Two practical facts follow. US labels must state that a product contains phenylalanine. And newborns are screened for PKU with a heel-prick blood test before they leave the hospital.

The researchers named the gaps themselves. That is more useful than a verdict. JECFA asked for better studies with longer follow-up. It asked for repeated diet questionnaires in cohorts that already exist. It also asked for randomized trials. Those should include the pathways tied to insulin control, metabolic syndrome, and diabetes.

Note what that is not. It is not a call to study diet soda on its own. It is a call to separate sweetener intake from the metabolic conditions that travel with it.

Aspartame carries a Group 2B label. That label rests on limited evidence in three separate areas. The cancer behind it is liver cancer. Every body that set an intake limit left that limit alone. Normal use sits far below both the 40 and the 50 mg per kilogram figures. For a sweetener with a similar history, see our page on saccharin.

• World Health Organization, IARC, and FAO/WHO JECFA, Aspartame hazard and risk assessment results released, July 14, 2023, accessed August 6, 2026
• U.S. Food and Drug Administration, Aspartame and Other Sweeteners in Food, accessed August 6, 2026