Sugar once made the world go round. As early as the reign of George I, the UK derived 1% of its annual GDP from this simple carbohydrate, a figure that had risen to 4% by the Age of Revolutions. Fortunes were made by it, with handsome cities like Bristol and Liverpool basically built on sugar money – and, of course, the backs of thousands of plantation slaves. Over recent decades, however, our century-old obsession for sugar has perhaps begun to relent. In the UK, for instance, a BMC Medicine article reported that the average sale of sugars in soft drinks dropped by 30% between 2015 and 2018, equivalent to a daily personal reduction of 4.6g. In Norway, meanwhile, the typical citizen consumed 24kg of sugar in 2018, down from 43kg at the turn of the century.

There are several ways to understand this phenomenon. One is the rising awareness of healthy eating, with a McKinsey poll finding that 50% of American consumers now prioritising healthy eating. Another is probably the stern hand of government: the UK is just one of several European countries instituting so-called sugar taxes, even as manufacturers are being pushed to tweak ingredients list. But if the avoidance of natural sugars is obviously a social good, we should hardly imagine that humanity’s love for sweetness has vanished altogether. On the contrary, as global average sugar consumption has now fallen to 21.4kg, reports the International Sugar Organization, substitutes have soared. Nowhere, is this clearer than the skyrocketing popularity of aspartame. First created in 1965 from two naturally occurring amino acids, this artificial sweetener is 200 times sweeter than traditional sucrose, reports EFSA. And that figure is amply matched by the sector’s growth: already a $9bn industry, Market Data Forecast suggests global aspartame could be worth $12bn by 2028.

“Most cancers have a long latency period: from exposure to [the] appearance of cancer. Research studies in humans [require] a longer time to evolve to the point where we have enough to evaluate the literature.”
Marjorie McCullough

But if aspartame is making fortunes as vast as the sugar boom of old, it arguably comes with baggage all its own. Even while it was being approved by the FDA, aspartame was dogged by worries about its health consequences, with some suspecting it could promote brain cancer. Similar concerns have persisted ever since, spanning everything from liver cancer to leukaemia. Earlier this year, the International Agency for Research on Cancer (IARC) made its own judgement. Linked to the UN and WHO, the IARC suggested that aspartame was “possibly carcinogenic” for humans, an announcement that spurred a storm of media attention. But amid the headlines, and as the long battle over aspartame suggests, the truth behind the IARC’s announcement is rather less straightforward, leaving aspartame’s ultimate impact decidedly fuzzy.

Something’s rotten

Aspartame has been a culinary staple for decades. “Aspartame has been widely used since the 1980s,” is how Harriet Burt of the World Action on Salt, Sugar and Health campaign group puts it. It is used “extensively” in soft drinks as varied as Diet Coke and Ribena Light and shadowed by other products too. If you’ve ever had ice cream, breakfast cereal or even a low-fat yogurt, chances are you’ve consumed aspartame. Quite aside from its sheer potency, this isn’t hard to understand. Boasting far fewer calories than natural sugar, it allows consumers to enjoy a treat without feeling too guilty.

Yet alongside this popularity, and as the IARC’s intervention in July 2023 vividly implies, aspartame has long been stalked by controversy. Even in 1974 when aspartame was first approved by the FDA, some critics argued that the research into its safety was flawed, suggesting it could be linked to brain cancer. Similar questions have persisted ever since. Through the 1980s, the US Centers for Disease Control and Prevention (CDC) investigated the potential for aspartame to cause various unpleasant side effects, including insomnia, nausea and diarrhoea. Though the organisation ultimately rejected such associations – arguing that the symptoms involved were common enough to have plausibly been caused elsewhere – the concerns have persisted. In 2006, for instance, scientists in Italy suggested that aspartame could cause leukaemia and lymphoma in rats. While later evaluations have severely criticised the study’s design, the controversy has continued to rumble into the following decade.

How to explain all this confusion? For Marjorie McCullough, the question can fundamentally be understood in terms of how science is done – especially when possible carcinogens are involved. “Early studies were conducted with animal models,” explains McCullough, senior scientific director of epidemiology research at the American Cancer Society. “Most cancers have a long latency period: from exposure to [the] appearance of cancer. Research studies in humans [require] a longer time to evolve to the point where we have enough to evaluate the literature.” Indeed, and as McCullough points out, though the “evidence from epidemiological studies in humans is growing”, clarity around various types of cancer remains limited.

No can do

When the IARC published its announcement that aspartame was “possibly carcinogenic” for human consumption, the world’s media could hardly restrain itself. ‘WHO’s cancer research agency to say aspartame sweetener a possible carcinogen’ is how Reuters put its scoop on the story, while the Express claimed that the sweetener “may” cause cancer. To an extent, the use of simplistic language after such a long and divisive scientific debate is unsurprising. Describing aspartame as a “hot topic”, Burt adds it’s “something a lot of people have a strong opinion on”.

Looking beyond the journalistic hype, however, what did the IARC actually say? Perhaps the most pressing thing to understand is that the organisation didn’t conduct any new research itself. Supported by a bevy of external experts, it instead analysed all the evidence that’s already been published. McCullough, for her part, was one of these outside advisers and agrees with the IARC’s overall findings, stating that aspartame is “a possible” cause of liver cancer. Like the IARC, meanwhile, McCullough argues that more research is needed, not least given the “emerging” evidence linking it to cancer in both animals and humans. Fair enough: as recently as 2021, a pair of scientists at Boston College suggested that evidence linking prenatal aspartame exposure to cancer in rodents was “very worrisome”.

Not that the IARC’s findings are necessarily catastrophic. Importantly, McCullough and her colleagues made no judgement on how much aspartame someone would need to consume to elevate their risk of cancer. That, the IARC leaves to the Joint FAO/WHO Expert Committee on Food Additives (JECFA), another international agency jointly administered by the UN and the WHO. In point of fact, JECFA recently commented on the ‘acceptable daily intake’ (ADI) of aspartame as previously approved by the European Food Safety Authority, and restated that the 40mg/kg limit still stood. This is significant not just because it puts regulators and external experts on the same page. If a can of diet soft drink contains between 200–300mg of aspartame, a 60kg person would need to consume 2,400mg of aspartame each day to surpass the ADI, the equivalent of eight to 12 cans.

Holistic discussion

Given that those who weigh more can enjoy an even higher ADI – and that the typical American drinks 2.6 glasses of soft drinks a day found Gallup’s annual Consumption Habits poll – could we be forgiven for breathing a collective sigh of relief? The experts suggest not. For one thing, McCullough points out that aspartame is included in many other products, not just soft drinks, meaning “it’s not implausible to reach the ADI”. For another, Burt warns that it can be hard to monitor consumption, especially when some products don’t state how much aspartame they contain. As she puts it: “Even if you wanted to, you couldn’t keep track of how much aspartame you are consuming.” Nor is this simply a personal problem. Because it isn’t included in national dietary surveys, Burt notes that aspartame consumption at a national level is a mystery too.

With that in mind, it makes sense that Burt would argue for government action around aspartame – much like the anti-sugar drives of recent years. “In relation to sugar,” she says, “we need policies to ensure the food industry reduces levels of sugar and non-sugar sweeteners, like aspartame, in their everyday products and protects our health from avoidable illnesses and early deaths.” The IARC, for its part, doesn’t make policy interventions, but you get the feeling McCullough would prefer a more holistic discussion as well. As she admits, “many things” can be done to reduce someone’s cancer risk, from doing exercise and staying thin to eating whole grains and avoiding red meat. Abstaining from alcohol is a good idea too. To put it differently – and whatever the truth about the sweetener itself – anyone serious about cancer should probably see aspartame as just one area of focus.