WHO says aspartame might cause cancer — but that most adult consumers don’t need to worry

By Nicholas Florko July 13, 2023

MATT ROURKE/AP

WASHINGTON — Aspartame, the popular artificial sweetener in diet sodas and chewing gums, may possibly cause cancer — but the risk appears to be very low for occasional consumers of these products, according to two reports released Thursday evening by the World Health Organization.

The first report, penned by the WHO’s International Agency for Research on Cancer (IARC), found “limited evidence” that aspartame may cause liver cancer. The second, from the Joint FAO/WHO Expert Committee on Food Additives (JECFA), reconfirmed the WHO’s previous recommendations that the sweetener is generally safe up until very large doses.

The seemingly contradictory findings stem from the two groups’ differing remits. The IARC, which found that aspartame was possibly linked to cancer, studies whether a substance has the potential to cause harm. The second group, JECFA, aims to estimate the actual risk that cancer or other potential harms will actually occur.

WHO officials emphasized during a press conference Wednesday that most casual consumers of beverages like Diet Coke and Diet Pepsi do not need to be concerned about their cancer risk from aspartame.

“Somebody who drinks a soda every once in a while … shouldn’t have a concern [about cancer],” said Francesco Branca, director of the Department of Nutrition and Food Safety at the World Health Organization. “We’re not advising companies to withdraw products nor are we advising consumers to stop consuming altogether, we’re just advising for a bit of moderation.”

However, WHO officials cautioned that the report’s findings could raise concerns for children who will more easily reach the daily recommended limit of aspartame, which is based on body weight.

“You’re right in saying that children may be at a higher risk,” said Branca. A 44-pound child would need to drink roughly four cans of Diet Coke per day to reach the maximum limit, according to the WHO’s recommendations.

Branca also recommended that heavy consumers of aspartame cut down on their consumption — though it’s unclear how many people in the U.S. currently come close to the recommended maximum daily dose, which is 40 milligrams of aspartame per 1 kilogram of body weight. For a 200-pound person, that would mean they would need to drink more than 18 Diet Coke cans per day to hit the daily limit.

“There’s only a very obvious recommendation to give … bring down the consumption,” Branca said, regarding frequent consumers of the sweetener.

The reports likely will not prompt immediate action from public health officials or beverage companies because of the low risk to typical consumers, but they’re likely to cause a massive public relations headache nonetheless.

In a letter dated Aug. 12, 2022, a top official at the U.S. Department of Health and Human Services urged the WHO not to conduct the two reviews simultaneously, given the groups’ different methodologies and likely differing conclusions.

“We are extremely concerned that conflicting determinations presented by IARC and JECFA would seriously undermine the confidence of the scientific process for both bodies and could further inflame the current climate of public skepticism about the validity of science and the scientific process,” the official wrote.

IARC’s determination of a possible cancer risk came primarily from its analysis of three large observational studies examining the correlation between liver cancer and consumption of artificially sweetened beverages, like diet colas. However, these large studies do not show causation, and both WHO groups noted they have significant flaws.

“The Working Group concluded that chance, bias, or confounding could not be ruled out with reasonable confidence in this set of studies. Thus, the evidence for cancer in humans was deemed ‘limited’ for [liver cancer],” the IARC group wrote in a summary paper published Thursday evening in the Lancet. The full evaluation from IARC is expected to be published “in the coming months,” according to Mary Schubauer-Berigan, the acting head of the IARC monographs programme at WHO.

WHO officials said Wednesday that they hope the reports will prompt more research into the potential risks of the sweetener.

“This is really more a call to the research community to try to better clarify and understand the carcinogenic hazard that may or may not be posed by aspartame consumption,” said Schubauer-Berigan.

The new analyses follow a May report from the WHO, which found that there’s little evidence to suggest artificial sweeteners, including aspartame, help reduce body fat and that they may increase risk for type 2 diabetes and cardiovascular problems.