WHO expected to declare artificial sweetener in Diet Coke could possibly cause cancer

LONDON – One of the world’s most common artificial sweeteners is set to be declared a possible carcinogen in July by the World Health Organisation (WHO), according to two sources with knowledge of the process, pitting it against the food industry and regulators.

Aspartame, used in products from Coca-Cola diet sodas to Mars’ Extra chewing gum and some Snapple drinks, will be listed in July as “possibly carcinogenic to humans” for the first time by WHO’s cancer research arm, the International Agency for Research on Cancer (IARC), the sources said.

The IARC classification, finalised earlier in June after a meeting of the group’s external experts, is intended to reflect if something is a potential hazard or not, based on all the published evidence.

It does not take into account how much of a product a person can safely consume. This advice for individuals comes from a separate WHO expert committee on food additives, known as JECFA (the Joint WHO and Food and Agriculture Organisation’s Expert Committee on Food Additives), alongside national regulators.

However, similar IARC classifications in the past for different substances have raised concerns among consumers about their use, led to lawsuits, and pressured manufacturers to change recipes and switch to alternatives. That has led to criticism that the IARC’s assessments can be confusing to the public.

JECFA is also reviewing aspartame use this year. Its meeting began at the end of June, and it is due to announce its findings on July 14, the same day that the IARC is expected to make public its decision.

Since 1981, JECFA has said aspartame is safe to consume within accepted daily limits. For example, an adult weighing 60kg would have to drink between 12 and 36 cans of diet soda – depending on the amount of aspartame in the beverage – every day to be at risk. Its view has been widely shared by national regulators, including in the United States and Europe.

An IARC spokesman said both the agency and JECFA’s findings were confidential until July, but added that they were “complementary”.


IARC said its conclusion represented “the first fundamental step to understand carcinogenicity”.

However, industry players and regulators had feared that making both announcements at around the same time could be confusing, according to letters from US and Japanese regulators seen by Reuters.

“We kindly ask both bodies to coordinate their efforts in reviewing aspartame to avoid any confusion or concerns among the public,” Mr Nozomi Tomita, an official from Japan’s Ministry of Health, Labour and Welfare, wrote in a letter dated March 27 to WHO’s deputy director-general Zsuzsanna Jakab.

The letter, reviewed by Reuters, also called for the conclusions of both bodies to be released on the same day, as is now happening. The Japanese mission in Geneva, where WHO is based, did not respond to a request for comment.

The IARC classification for aspartame can have a huge impact.

In 2015, its committee concluded that glyphosate, a herbicide, is “probably carcinogenic”. Years later, even as other bodies like the European Food Safety Authority (EFSA) contested this assessment, companies were still feeling the effects of the decision.

Germany’s Bayer in 2021 lost its third appeal against US court verdicts that awarded damages to customers blaming their cancers on use of its glyphosate-based weedkillers.

The IARC’s decisions have also faced criticism for sparking needless alarm over hard to avoid substances or situations. It had previously classified working overnight and consuming red meat as “probably cancer-causing”, and using mobile phones as “possibly cancer-causing”, similar to aspartame.

“IARC is not a food safety body and its review of aspartame is not scientifically comprehensive and is based heavily on widely discredited research,” said secretary-general of the International Sweeteners Association (ISA) Frances Hunt-Wood.

The association, whose members include food companies Mars Wrigley, a Coca-Cola unit, and Cargill, said it had “serious concerns with the IARC review, which may mislead consumers”.

Aspartame has been extensively studied for years. Last year, an observational study in France of 100,000 adults showed that people who consumed larger amounts of artificial sweeteners – including aspartame – had a slightly higher cancer risk.


It followed a study from the Ramazzini Institute in Italy in the early 2000s, which reported that some cancers in mice and rats were linked to aspartame.

However, the first study could not prove that aspartame caused the increased cancer risk, and questions have been raised about the methodology of the second study, including by EFSA, which assessed it.

Aspartame is authorised for use globally by regulators which have reviewed all the available evidence. Major food and beverage makers have for decades defended their use of the ingredient.

The IARC said it had assessed 1,300 studies in its June review.

Recent recipe tweaks by soft drink giant Pepsico demonstrate the struggle the industry has when it comes to balancing taste preferences with health concerns. Pepsico removed aspartame from its sodas in 2015, bringing it back a year later, only to remove it again in 2020.

Listing aspartame as a possible carcinogen is intended to motivate more research, said the sources close to the IARC. The move will help agencies, consumers and manufacturers draw firmer conclusions.

It will also likely ignite debate once again over the IARC’s role, as well as the safety of sweeteners in general.

In May, WHO published guidelines advising consumers not to use non-sugar sweeteners for weight control. The guidelines caused a furore in the food industry, which argued that such sweeteners can be helpful for consumers wanting to reduce the amount of sugar in their diet.


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