Explained | What does aspartame being ‘possibly carcinogenic’ mean?

The World Health Organization (WHO) recently declared aspartame, an artificial sweetener used in the food industry, as a possible carcinogen. Substances that potentially cause cancer are called carcinogens.

Aspartame is present in a wide range of food products – sugar-free diet soda, ice tea, ice cream, low fat yoghurt, cereals, and medicines such as chewable vitamins. In fact, it is quite difficult to avoid consuming at least some amount of aspartame in our diet.

The expert committee

The announcement from WHO has created a lot of buzz, and with it, some anxiety. Are we unwittingly exposed to a carcinogen?

There is more to this than meets the eye. The devil, as always, is in the details.

The report in which aspartame was evaluated – and several such declarations that christen a substance as being carcinogenic – are authored by a committee of experts under the authority of the International Agency for Research on Cancer (IARC).

The agency, headquartered in Lyon, France, was established under the WHO in 1965 with a mandate to study the causes of cancer. To date, the IARC has assessed more than a thousand substances or putative risk factors for their roles in carcinogenesis.

The expert committee

In order to create a common reference point for the recommendations that arise from the deliberations of the expert working committees, the IARC uses a grading system.

Grade 1 substances are factors known to cause cancer in humans, with sufficient evidence supporting their carcinogenicity. This category includes smoking, asbestos, and processed meats, all of which have been linked to a higher cancer hazard.

Grade 2 substances, or exposures, are classified as being probably or possibly carcinogenic to humans. Within Grade 2, there are two subcategories. ‘2A’ includes agents that are probably carcinogenic in humans, supported by ample evidence of carcinogenicity in experimental animals but limited data regarding humans. Red meats, DDT pesticide, and night-shift work fall into the 2A category.

On the other hand, ‘2B’ includes agents that are possibly carcinogenic in humans but for which there is insufficient evidence of carcinogenicity in animals and limited or inadequate evidence in humans. For example, cell phone radiation and occupational exposure as a hairdresser falls under 2B.

A Grade 3 recommendation is assigned to agents that can’t be classified as carcinogenic due to limited or inadequate data, even in experiments. Coffee, mercury, and paracetamol are examples of agents in this category.

Risk v. hazard

While the IARC grading system assesses the hazards with a substance for carcinogenicity, it does not measure the risk of cancer itself. A hazard is a source of harm – whereas a risk is the chance that you will be harmed by that hazard.

IARC only categorises substances or exposures based on the strength of the available data about its properties and behaviour for carcinogenicity. It does not incorporate details regarding the level of 
harm each substance or exposure may pose to individuals.

For example, both smoking and the consumption of processed meat are graded as carcinogens. But it is quite easy to comprehend that consuming small quantities of processed meat will not have the same level of harm as any amount of tobacco exposure.

So it is not advisable to compare the IARC grades of two agents. A Grade 1 classification for both smoking and processed meat simply indicates that both agents can potentially cause cancer in certain situations. It does not provide any insight into the chance of a person developing cancer when exposed to such agents.

In other words, exposure or substances within the same category of IARC grade does not carry the same risk – but it bears the same hazard.

Another expert committee

In this context, another report that was (strategically and effectively) published at the same time as the IARC’s report on aspartame becomes very relevant. The U.N. Food and Agriculture Organization and the WHO Joint Expert Committee on Food Additives (JECFA) separately evaluated the risk or odds of developing cancer with the use of aspartame. Contrast this with the goal of the IARC programme, which is to identify the potential for dietary or non-dietary exposure of an agent to cause cancer. The complementary publication of these two committee reports was deliberate and well-considered.

In particular, the JECFA on aspartame reaffirmed prior deliberations by the same group, that aspartame is safe for human consumption up to a limit of 40 mg/kg of body weight. For reference, a can of an aerated beverage (‘diet’ variety) contains 200-300 mg of aspartame. The JECFA committee noted that the concentration of aspartame metabolites in plasma was not found to increase after the substance is hydrolysed in the gut. Its review of the available evidence also suggested no consistent association with aspartame 
use and cancer incidence.

Both the IARC and JECFA evaluations were rigorously examined by independent experts, who reviewed the scientific data gathered from various reputable sources, including peer-reviewed papers, government reports, and studies carried out for regulatory purposes.

Processed foods

Although the IARC’s report on the hazard of aspartame for cancer suggested limited evidence from human and animal studies, and qualified the carcinogenicity to be grade 2B (‘possible carcinogenic’), the JECFA report asserts that the risk threshold for the food additive remains within the acceptable limits for the average person consuming processed foods.

In sum, while aspartame has been classified as a ‘possible carcinogen’, it is still safe to be used as a food additive in various products in reasonable quantities. But taking all the available evidence together, ultra-processed and processed foods – which are food products that have undergone some degree of processing from their natural states – are not good for health and well-being. The IARC and JECFA reports highlight that less is more when it comes to any food additives or taste enhancers, including sugar and artificial sweeteners.