On 29 June 2023, the soda industry was bracing for a fresh wave of controversy. A media leak had suggested that a research arm of the World Health Organization (WHO), which had been reviewing the artificial sweetener aspartame, was planning to classify the additive as possibly cancer-causing.
The sweetener – included in candy, soft drinks such as Diet Coke and Diet Pepsi, and common items such as toothpaste – has long been dogged by questions about potential health risks. And such a determination could disrupt consumers’ spending and billions in annual sales.
By the end of the day, the International Council of Beverage Associations – a global group representing soft drinks manufacturers and regional industry groups – issued a statement to pre-empt the coming report. In the press release, the group’s executive director, Kate Loatman, said: “Public health authorities should be deeply concerned that this leaked opinion contradicts decades of high-quality scientific evidence and could needlessly mislead consumers.”
A few weeks later, the WHO group, formally known as the International Agency for Research on Cancer (IARC), made its evaluation public: aspartame was “possibly carcinogenic to humans”, it said, calling for further research on the link between the additive and cancer. The announcement made waves in the press and drew support from public interest groups. But it wasn’t the radical industry-gutting statement that food and drink producers feared.
Now, about a year later, questions about artificial sweeteners’ health effects remain largely unsettled.
Most of the artificial sweeteners used today were first developed in the 19th and 20th centuries, driven by consumer demand and producer constraints like sugar costs and shortages.
The first widely commercialized sweetener, a chemical compound called saccharin, was accidentally discovered in 1879 by a chemist who had tasted the residue on his hand after studying coal tar. In 1965, aspartame would be discovered in a similar fashion by a chemist named James M Schlatter, who had been conducting research on anti-ulcer drugs. Schlatter brought his hand to his mouth after dipping them into a mixture of amino acids and took delight in the unexpected flavor. “I licked my finger, and it tasted good,” he said, according to a 1982 Washington Post story on his discovery.
These ingredients – among others like sucralose and cyclamate – were quickly adopted by food manufacturers as cheap sweeteners that could satiate sugar-craving consumers while being marketed as low-calorie or healthful.
“Cyclamates, saccharin, aspartame and sucralose may have stories of accidental origins, but their invention, marketing, consumption and even anti-consumption have been very intentional,” wrote cultural historian Carolyn Thomas in Empty Pleasures: The Story of Artificial Sweeteners from Saccharin to Splenda. “They have made and lost fortunes, forged new partnerships between businesses and destroyed others, transformed the landscape of women’s magazines, given birth to a food industry, made consumption without consequence a viable pursuit, and changed the meaning of the term ‘diet’ itself.”
Despite their long history, the debate around whether artificial sweeteners are “healthy” – or harmful – remains unresolved. That brings us back to last year’s IARC classification.
The agency first began probing aspartame at the recommendation of Center for Science in the Public Interest, a consumer health non-profit that has been advocating for greater scrutiny of aspartame for over a decade.
Among artificial sweeteners, aspartame “is the one that we have the most concern about,” said Thomas Galligan, the center’s principal scientist for food additives. “The evidence is strongest there … We feel it has been pretty credibly linked to cancer.”
The Food and Drug Administration (FDA), which regulates food additives, first approved aspartame as a tabletop sweetener in 1974, for use in soda in 1983, and for general use in 1996. Throughout this stretch, questions loomed over both the ingredient and the process by which FDA had approved it. In 1982, in response to controversy, a government watchdog agency was ordered to review the approval process, and it published a report finding that the FDA had adequately followed protocol.
However, since the 1990s, a steady drumbeat of new and often conflicting research has come out on the additive, most notably a series of studies by the Ramazzini Institute, a research organization in Italy. Whereas prior research looked at the effects of aspartame consumption on relatively small groups of rats for limited stretches of time, the institute’s research included significantly larger sample sizes and studied the lab animals over the course of their entire lifetimes until natural death, ultimately finding higher levels of malignant tumors in rats that had consumed the artificial sweetener.
The research stirred furor and questions about its rigor, merits and data interpretation. Still, in response to the research, consumer welfare groups began calling on regulatory and health bodies like the FDA and the WHO to re-evaluate aspartame.
But last year’s designation didn’t actually clear the air about aspartame. If anything, it simply articulates just how much we don’t yet know. IARC classifies foods in one of four groups based on the strength of existing research: carcinogenic, probably carcinogenic, possibly carcinogenic, and not classifiable as carcinogenic.
“What they’re essentially doing is evaluating the strength of evidence that links a certain agent to the ability to cause cancer in humans,” Galligan said.
Possibly carcinogenic means that evidence exists of a link, but it’s weak. “The door is still open that aspartame could be carcinogenic,” said Eva Schernhammer, an adjunct professor of epidemiology at Harvard’s TH Chan School of Public Health and a member of the IARC evaluation on aspartame. “That door could not be completely closed after the assessment.”
Easy answers about artificial sugar defy us, in part because it’s really challenging to study their long-term effects. Research conducted on animals like rats are imperfect analogs to how exposure might affect humans. Even large-scale research involving human consumption has limits.
The studies that look at the relationship between sweeteners and human bodies are hazy because they’re largely observational, not controlled. Many rely on self-reported sweetener consumption, meaning that numbers can be smudged by memory and human error. Even when there are links between higher rates of cancer and aspartame consumption, it’s impossible to say whether aspartame caused the condition or somehow factored into the illness.
In 2022, researchers in France published the results of a giant cohort study, composed of more than 100,000 participants, evaluating the link between cancer risk and artificial sweeteners. The study found that aspartame in particular was associated with a 15% increased risk of cancer. However, the study couldn’t determine actual causation. The links could be explained by factors like self-selection among participants, other variables or mere probability.
To conduct a truly rigorous study of artificial sweeteners and cancer risk would be nearly impossible, Schernhammer explained, requiring meticulous control and monitoring of sweetener intake among large groups of humans for a decade or longer. That would be logistically challenging to execute and potentially unethical.
After the IARC published its classification of aspartame, numerous groups criticized the move, arguing that it would sow confusion among consumers and went against existing consensus that the sweetener was safe up to certain consumption limits.
“Aspartame is one of the most studied food additives in the human food supply,” the FDA wrote after the announcement. “FDA scientists do not have safety concerns when aspartame is used under the approved conditions.” FDA sets its daily acceptable intake of aspartame at no more than 50mg per kilogram of body weight.
That’s confusingly different from the recommendation from the WHO’s expert committee on food additives, which is separate from its cancer research group. This agency holds that consumers should limit their daily aspartame intake to 40mg per kilogram of body weight. While there’s no consensus on what difference 10mg a day makes, any variation in impact is most likely to be felt among drinkers who weigh less, particularly young children and older people.
Schernhammer agrees with the sentiment that limited consumption of aspartame-sweetened products is probably fine – with the caveat that water is indisputably a healthier option compared to soda and diet soda sweetened with aspartame alike.
Still, demand for the latter isn’t going to change anytime soon. Between 2023 and 2028, according to one projection, global revenue for artificial sweeteners is forecasted to jump by 43% to $33.8bn.
