WHO warning: Is diet coke really cancerous?

One of the world’s most common artificial sweeteners is set to be declared a “possible carcinogen” next month by the cancer research arm of the World Health Organisation (WHO).

Aspartame is one of the world’s most common artificial sweeteners and is used in a wide range of diet soft drinks, sugar-free chewing gum, sugar-free ice cream, sugar-free breakfast cereals, etc.

Aspartame is 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 the International Agency for Research on Cancer (IARC).

The IARC ruling, finalised earlier this month after a meeting of the group’s external experts, is intended to assess whether 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 Organization’s Expert Committee on Food Additives), alongside determinations from national regulators.

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

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

Since 1981, JECFA has said aspartame is safe to consume within accepted daily limits. For example, an adult weighing 60 kg (132 pounds) 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.

Aspartame has been extensively studied for years. Last year, an observational study in France among 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 who have reviewed all the available evidence, and 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 drinks giant Pepsico demonstrate the struggle the industry has when it comes to balancing taste preferences with health concerns. Pepsico removed aspartame from 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, which will help agencies, consumers and manufacturers draw firmer conclusions.

Last month, the WHO published guidelines advising consumers not to use non-sugar sweeteners for weight control. The guidelines caused a furore in the food industry, which argues they can be helpful for consumers wanting to reduce the amount of sugar in their diet.