Don’t overreact to the cancer risk of sugar-free sweeteners

a large 2022 study followed more than 100,000 people in France and found a possible small increased cancer risk in heavy users of artificial sweeteners.
a large 2022 study followed more than 100,000 people in France and found a possible small increased cancer risk in heavy users of artificial sweeteners.


  • These are ‘possibly carcinogenic’ just as our use of mobile phones is

There was good reason to avoid products with the artificial sweetener aspartame even before the World Health Organization classified it as a “possible carcinogen." Now diet soda drinkers might want to quit their cans. But first, some perspective: “Possible carcinogen" is the weakest of three bins into which WHO classifies anything that’s even remotely tied to cancer in any kind of study. It labels substances with more serious links to cancer as “probable carcinogens" and if the evidence is really strong, “carcinogenic to humans." That middle category includes things that many of us consume routinely, including alcoholic beverages and very hot drinks (linked to oesophageal cancer). The evidence behind possible carcinogens is more tenuous. The low-frequency radiation emitted by cell phones is in that category because studies have suggested weak associations with cancer in animals.

In the case of aspartame, some studies show rats fed high doses of aspartame are more likely to get brain cancer and several other malignancies. Adding to the concern, a large 2022 study followed more than 100,000 people in France and found a possible small increased cancer risk in heavy users of artificial sweeteners. But studies like this can’t prove that the sweeteners caused cancer. It’s possible that the group consuming more sweeteners also ate more processed food, or were more obese, or there was some other link.

A better way to get information would be to treat the humans more like the lab rats, feeding some people aspartame and comparing them to control groups. And now someone has done that, setting up a randomized controlled trial. The study wasn’t set up to find a cancer link, but it did connect artificial sweeteners with the same risks associated with sugar. Several other studies have linked aspartame to spiking blood sugar, and in the longer term, to higher blood sugar and expanded waistlines. Perhaps there’s just no risk-free soda.

The FDA approval of aspartame in 1981 was mired in controversy. Former US defense secretary Donald Rumsfeld ran the company that makes aspartame, G.D. Searle & Co, and was also part of Ronald Reagan’s transition team. As soon as he was elected, Reagan appointed a new FDA head who reportedly stacked a scientific panel to push through aspartame’s approval. Today aspartame is in diet drinks, gum, ice creams, puddings, cereals and other packaged foods marketed as sugar-free. Would it have been approved if not for Rumsfeld’s influence? Maybe.

Massive waves of death did not follow the use of aspartame, but there was no improvement in rising rates of obesity or Type 2 diabetes. Fake sugar hasn’t made America healthier. That randomized controlled trial helps explain why. The study, published in 2022 in the journal Cell, compared six groups, four consuming each of four different artificial sweeteners and two control groups. The sweeteners were Sucralose, Aspartame, Stevia and Saccharine. One control group got no sweetener and the other got a tiny amount of real sugar, the same amount added to artificial sweetener sachets to offset bitterness.

The study’s leader, Eran Elinav of the Weizmann Institute of Science in Israel, told me he wanted to explore whether artificial sweeteners were interfering with gut microbes—the microbiome. Two control groups showed no changes in their microbiome composition or their blood sugar control. The four that got artificial sweeteners showed changes in both after just two weeks of consuming an amount similar to what consumers might get drinking a couple of diet sodas a day. The point, Elinav said, is that these substances don’t just pass harmlessly through the body. His results, he said, were interesting because the subjects getting the sweeteners reacted very differently, some showing almost no change and others substantial changes in microbial communities and blood sugar.

Even a low probability of risk might be enough reason for some people to switch to water or unsweetened drinks, given the way recent studies cast doubt on any metabolic benefit. What should people with a sweet tooth do? Elinav said he absolutely does not want people to interpret his study to say they should switch back to drinks heavily sweetened with regular sugar or corn syrup. These are tied to all sorts of health problems, including cancer.

But it’s impossible to prove beyond doubt that anything, even cell phones, will never cause anyone to get cancer. So we have to weigh the risks and benefits. When I interviewed American Cancer Society head Otis Brawley about cell phones, he acknowledged the possibility of a link, but we were both talking on our cell phones at the time. When I talked to Erinav, he wasn’t drinking a diet soda—and he told me he opts for water. ©bloomberg

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