On the strength of that data, substances are put into one of four categories: carcinogenic; probably carcinogenic; possibly carcinogenic; or not classifiable. Reuters reported recently that aspartame would be labelled “possibly carcinogenic”. That would put the sweetener, marketed under brand names such as Equal and Canderel, in the same category as gasoline and aloe vera extract. A formal announcement is tabled for 14 July, along with a paper in Lancet Oncology.
But the IARC pronouncement isn’t the critical one. Whether a hazard becomes a health risk depends on factors such as exposure, dose and preventive measures (sunshine is a largely unavoidable carcinogen, with sunscreen a mitigation). That is where the second WHO-linked committee, on food additives, comes in. Its statements — on acceptable daily intake and dietary exposure — will be the ones to watch out for.
The committee previously assessed aspartame, also known as E951, in 1981, setting an acceptable consumption limit at 40mg per kg of body weight per day — or 12 cans of Diet Coke a day for a 60kg person. That has reassured food safety agencies, including in the US, UK and EU. But doubts have accumulated since, partly because of observational studies that hint at slightly higher rates of cancer in consumers. A 2022 analysis of nearly 103,000 people reported that those who consumed higher levels of artificial sweeteners, including aspartame, were 1.15 times more likely overall to develop cancer than those who consumed none.
Observational studies, though, can point only to association, not cause and effect; other factors could be at play. Plus, “reverse causality” cannot be ruled out: people who are obese, and therefore already face a higher cancer risk, might be more likely to choose artificial sweeteners. The sheer variety of non-sugar sweeteners — including sucralose, saccharin and the plant-derived stevia — and their varying permutations in studies, also makes the science hard to read.
Animal studies can partly fill the evidence gap: Italy’s non-profit Ramazzini Institute reported more than a decade ago that aspartame-fed rats developed dose-related tumours. But rats are not humans. Both the charity Cancer Research UK and the UK’s Food Standards Agency maintain that aspartame is safe.
Nonetheless, IARC undertook its latest re-evaluation as a high priority because of “emerging cancer evidence in humans and in laboratory animals”. The International Sweeteners Association complained that “IARC is not a food safety body...aspartame is one of the most thoroughly researched ingredients in history”.
Those complaints artfully dodge an inconvenient truth, which is that evidence can change and that non-sugar sweeteners, including aspartame, are not the healthy option that many consumers believe. In May, the WHO recommended that non-diabetics steer clear of NSS because evidence suggests they do not reduce body fat and may be linked to an increased risk of type 2 diabetes, cardiovascular disease and death. The best approach, it says, is to eat a less sweet diet overall.
More widely, the additives are commonly found in ultra-processed foods, which have been linked to obesity and ill-health by, among others, campaigning doctor and author Chris van Tulleken. There is little to be lost, and potentially much to be gained, by going sour on sweeteners.
The writer is a science commentator
Written by: Anjana Ahuja
© Financial Times
