There is ample evidence that artificial sweeteners are of no benefit for weight loss or for those with diabetes. At this stage, the evidence may not be strong enough as to whether most people would consume enough to provide a substantial increase in the risk of various cancers.

However, there is no doubt that artificial sweeteners maintain a 'sweet tooth'. And for that alone, we should certainly focus - as the WHO has done - on encouraging policy makers to focus on reducing the consumption of sugar and its substitutes in infants and young children still forming taste preferences.

The International Agency for Research on Cancer (IARC) is reported to be about to classify the sweetener aspartame as a class 2B carcinogen (Possibly carcinogenic to humans). This means that there is some weak evidence of carcinogenicity. To put this in perspective, hot beverages are in the IARC class 2A (probable carcinogens). So we have less evidence for aspartame being a carcinogen that for drinking hot beverages.

As well, the IARC is looking at ANY possibility of cancer, not risk. So while aspartame might possibly induce cancer under some circumstances, the vast majority of people may not be exposed to the risk. Indeed, the most recent systematic review of non-sugar sweeteners that came out in March found no consistent evidence of carcinogenicity from epidemiological studies and no evidence relevant to humans of carcinogenicity in animals. And many studies have shown no risk for non-Hodgkin’s leukaemia, myelomas, lymphomas, hematopoietic cancer and glioma.

In short, the evidence of any human risk is very weak indeed, and if you are not going to worry about your risk from a hot cuppa then the aspartame you put in it is even less of a worry.

The label “possible cancer risk” is not strong and does not suggest that we should all stop consuming aspartame-containing products altogether. However, it is probably a good idea to monitor your consumption of such things as artificially sweetened soft drinks for a number of other reasons such as the effects on your kidneys and bone density. 

So, from a toxicological perspective, this could serve as a heads-up for people who habitually drink several cans of soft drinks per day for them to drink more water.

Another point is that there was a scare about saccharin and cancer years ago but it turned out to be an effect only seen in rats due to the distinct biochemistry of their urine. However, this did not stop the popularity of saccharin from declining due to the news being announced.

The IARC and WHO's recent advice and concerns on the use of non-nutritive sweeteners are of general health concern, and not only a matter of risk for cancer.

There is now no acceptable public health justification for their promotion in weight management. Preference for sweetness itself, over and above sugar as a nutrient, is a consideration, given the extent of human biology for sweet receptors beyond the tongue, in other organs and the gut microbiome.

There are outstanding risk-benefits for sweeteners other than aspartame, such as sucralose, and consumers are challenged to discriminate one from another.

Perhaps more than any other consideration is that these sweeteners are found in processed foods which also add to the massive burden of plastic waste through the plastic bottles and wrappings in which they are found. These plastics themselves also often contain troubling endocrine disruptor effects. This is the area of science we need more research on right now.

We really need to wait and see the full IARC evaluation before we can make any firm conclusions.  Without that, we are really shooting in the dark.  We don’t know what the terms of the assessment were, or what criteria they used to rule evidence in or out.

What we can say is that IARC generally reviews the existing scientific literature on a particular substance or process, then weighs the evidence as to the likelihood said substance or process may be able to cause cancer under certain conditions or exposure.  In this case, the IARC are apparently going to list aspartame as a ‘possible carcinogen’ (the same as it previously classified eating red meat and using mobile phones), which means there is some evidence that it can cause cancer in humans but at present it is far from conclusive.  But we really can’t be sure of anything until a formal announcement is made.

It is also important to note that just because something may possibly cause cancer does not mean that it automatically does if you are exposed to it.  The dose makes the poison.

For example, we know UV light in sunlight causes cancer, that’s why we put on sunscreen at the beach – but we don’t put on sunscreen when we go outside in winter even though we are still exposed to sunlight, why?  Because the dose is lower in winter.

Similarly, we know that smoking causes cancer but that doesn’t mean that I will get cancer if one day I happen to breathe in some second hand smoke.

Like other food additives, Aspartame had to undergo robust safety evaluation before it was approved for use in food.  It is the world’s most widely used artificial sweetener and current evidence is that it is safe at current levels of consumption.”