Should you kick your Diet Coke habit? As a public health expert, I’m not too worried | Gideon Meyerowitz-Katz

We’ve been worried about artificial sweeteners and human health for decades. I remember when I was growing up a lot of parents would tell their kids to be careful about artificially sweetened things because they could cause all sorts of nasty conditions. In my teens a friend’s mother was convinced that her daughter’s Diet Coke habit was going to give her no end of issues later in life.

The latest news is no different. Aspartame, one of the most commonly used artificial sweeteners in the world, has made headlines as a cancer risk. This is because the International Agency for Research on Cancer, a World Health Organization body, reclassified aspartame as a class 2B carcinogen, which means that it officially – according to the IARC – is a “possible” cancer risk.

As a habitual Coke Zero drinker (both Diet Coke and Coke Zero contain some aspartame, although Diet Coke has more) this news could have been alarming. But as an epidemiologist who has looked into the question of the health impacts of aspartame, I don’t think there’s too much reason to worry.

The first thing to note is what a class 2B carcinogen actually is. The IARC estimates cancer risk to be one of four categories: 1 – causes cancer; 2A – probably causes cancer; 2B – possibly causes cancer and 3 – no evidence available on cancer risk.

That means that aspartame is now in the lowest possible risk category for cancer-causing substances that the IARC produces, because a class 3 carcinogen technically just means that it can’t be assessed due to lack of evidence. Class 2B means there is a vague and unproven risk that something might cause cancer, not that it does or is likely to.

Many people don’t realise how many everyday, normal things have some evidence that they could cause cancer. Other things that are on the class 2B list include caffeic acid, which is found in coffee, aloe vera, nickel, ginkgo biloba extract (a common supplement), and coconut oil products. None of these things get quite the same attention as aspartame, presumably because there’s nothing we love to hate quite as much as something artificial.

We don’t yet know why the IARC made the decision to reclassify aspartame as a possible cancer risk, because the decision is yet to be released, but it’s a bit of a surprising thing to do. While industry claims that aspartame is the most studied chemical in the world are a bit overblown, it does have a strong safety record. Numerous studies since the 1980s have failed to find any consistent link between aspartame and cancer. These include large epidemiological papers involving hundreds of thousands of people and, while there’s occasionally some indication of an increased risk, it’s rarely supported when you look at all of the studies together. One French study found an increased risk of certain cancers for people who consumed a lot of aspartame but these same risks have not been seen elsewhere in the literature.

It’s also important to remember that the IARC doesn’t take the magnitude of the risk into account – it just decides on a yes/no question about whether something causes or is likely to cause cancer. Red meat is considered to be a class 2A carcinogen – which means it’s more likely than aspartame to cause cancer, according to the IARC – but you have to eat a large amount of red meat to seriously increase your risk.

Similarly, the magnitude of aspartame risk is, to the individual, very small. Taking the results of the French study I noted above at face value, going from having absolutely no aspartame to drinking a can of Coke Zero a day for a decade would raise your risk of cancer from 3.1% to 3.3%. This is why most regulatory agencies across the world, including the Australian and European regulators, have deemed aspartame safe at levels of human intake.

At a population level, these risks aren’t meaningless. If 1 million Australians suddenly took up an aspartame habit, and it does indeed cause cancer at this sort of rate, that would be an additional 2,000 cancers across the country by 2033.

But for individuals, the risk from aspartame really isn’t something that is likely to impact your life. I know that I, for one, am going to keep drinking the occasional Coke Zero.

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