Aspartame, a low-calorie sweetener, has been labeled "possibly carcinogenic" by the WHO's cancer research division.

According to the Lyon, France-based International Agency for Research on Cancer (IARC), the decision was made on July 14 and was based on scant evidence for liver cancer found in human and rodent research.

The Joint FAO/WHO Expert Committee on Food Additives (JECFA) stated that the recommended daily limits for the sweetener, which is included in a vast array of food and beverage products, would not alter.

"There was no convincing evidence from experimental or human data that aspartame has adverse effects after ingestion, within the limits established by previous committee," said Francesco Branca, director of the WHO's Department of Nutrition and Food Safety, at a press conference on July 12 in Geneva, Switzerland.

According to Mary Schubauer-Berigan, acting leader of the IARC Monographs programme, the new classification "shouldn't really be taken as a direct statement that indicates that there is a known cancer hazard from consuming aspartame" at the press conference. This is more of a request to the research community to try to better define and comprehend the carcinogenic risk that aspartame use may or may not pose.

Aloe vera extracts, traditional Asian pickled vegetables, some automotive fuels, and several chemicals used in dry cleaning, carpentry, and printing are among the other compounds categorized as "possibly carcinogenic." Additionally, processed beef and red meat have been designated as "carcinogenic" by the IARC.

enticing science
Aspartame is used in more than 6,000 items globally, including diet drinks, gum, toothpaste, and chewable vitamins. It is 200 times sweeter than sugar. It was given the go-ahead to be used as a sweetener by the US Food and Drug Administration (FDA) in 1974, and the JECFA established an acceptable daily intake (ADI) of 40 milligrams per kilogram of body weight in 1981. This equates to around 2,800 milligrams per day for the average adult, or 9–14 cans of diet soda.

Over the past forty years, there have been a number of debates about the artificial sweetener, which have linked it to a higher risk of cancer and other health problems. However, the FDA and the European Food Safety Authority's reassessments found insufficient proof to lower the ADI.

A high-priority assessment of a number of chemicals, including aspartame, was suggested by an advisory panel to the IARC in 2019 based on newly available scientific data. Three studies that looked at the intake of artificially sweetened beverages provide the IARC with evidence of a connection between aspartame and liver cancer.

One of these studies, which was published online in 2014, followed 477,206 participants over the course of more than 11 years in 10 different European nations and discovered a link between consumption of sweetened soft drinks, including those containing aspartame, and an increased risk of hepatocellular carcinoma1. Drinking artificially sweetened beverages was linked to liver cancer in diabetics, according to a 2022 US study2. In the third study, which involved 934,777 US citizens between 1982 and 2016, researchers discovered that both men and women who consume artificially sweetened beverages have an increased risk of pancreatic cancer3.

The consumption of beverages with artificial sweeteners served as a stand-in for aspartame exposure in these research. According to Mathilde Touvier, an epidemiologist at the French National Institute of Health and Medical Research in Paris, such proxies are quite trustworthy but may not always provide a perfect assessment of intake.

Touvier co-authored a second study that was evaluated by the IARC and took into account aspartame consumption from other food sources, such as soft drinks, dairy products, and tabletop sweeteners. According to the research, among 102,865 persons in France, those who drank more aspartame (but less than the ADI) had an elevated risk of breast cancer and malignancies linked to obesity4.

According to Touvier, the study demonstrates "a statistically significant increased risk, robust across many sensitivity analyses." However, "for the time being, it hasn't had enough statistical power to investigate liver cancer."

Not always trustworthy
The JECFA also examined research linking aspartame to blood, liver, and breast cancers, but concluded that the results were inconsistent. The studies' design flaws prevented them from excluding confounding variables and they relied on participants' self-reports of their daily dietary aspartame intake.

The most dependable diet records are not always available. Aspartame isn't the only substance we consume. According to William Dahut, chief scientific officer of the American Cancer Society with a base in Bethesda, Maryland, it is a component of a mixture of chemicals and other things.

The sweetener degrades in the body into phenylalanine, aspartic acid, and methanol as its three byproducts. According to Branca, "These three molecules are also found when other food or drink products are consumed." As a result, aspartame cannot be found by blood testing. That is a restriction on our ability to comprehend its implications.

Because it is converted into formic acid, which has the ability to harm DNA, methanol has the potential to cause cancer. Paul Pharoah, a cancer epidemiologist at Cedars-Sinai Medical Center in Los Angeles, California, claims that methanol can harm your liver and increase your risk of developing liver cancer if you consume enough of it. However, he continues, the quantity of methanol produced by the breakdown of aspartame is negligible.

The IARC notes that more research is required to examine aspartame's effects on metabolic systems and its connections to other disorders. Touvier continues, "This research will also add additional pieces of data to the overall picture.

Cite this article as: 10.1038/d41586-023-02306-0