Is Aspartame Safe? The Evidence Behind the Possible Carcinogenic Sweetener

The World Health Organisation’s position on aspartame, and artificial sweeteners has been released – and in general, I was curious and open-minded to see the evidence behind their recommendations.

What is Aspartame?

Aspartame is a common artificial sweetener that is used as a table-top sweetener and in many food and beverage products, such as diet drinks, chewing gum, yoghurt, sweets, weight-control products, and medication like cough drops and chewable vitamins. It has been widely studied for its safety and health effects, but there is still some controversy and confusion about its potential risks and benefits.

Is Aspartame Safe for Human Consumption?

The safety of aspartame was reassessed by the International Agency for Research on Cancer (IARC) and the Joint Expert Committee on Food Additives (JECFA) – and concluded as follows:

• IARC classified aspartame as possibly carcinogenic to humans
• JECFA reaffirmed the acceptable daily intake (ADI) of 40 mg/kg body weight for aspartame, which means it is safe to consume daily within this limit

These two reports may seem contradictory, but they are actually complementary and reflect different aspects of the evaluation of aspartame.

The IARC’s assessment is based on the hazard identification of aspartame, which means identifying its specific properties and its potential to cause harm, like cancer.

JECFA’s assessment is based on the risk characterisation of aspartame, which means estimating the probability and severity of harm, at different levels of exposure.

Based on IARC’s assessment, aspartame will be added to the Group2B classification — possibly carcinogenic to humans. To be in this category “limited but not convincing, evidence for cancer in humans or convincing evidence for cancer in experimental animals, but not both” is required.

The IARC classified aspartame as possibly carcinogenic to humans based on limited evidence for cancer in humans and limited evidence evidence in experimental animals. 

You might be surprised by what else is in Group 2B — aloe vera leaf extract, kava extract, ginkgo biloba extract, and maybe less surprisingly gasoline, chloroform, and lead. The WHO does not quantify the risk or set limits of exposure, so we don’t know how risky aspartame is.

What is the Acceptable Daily Intake Level?

Currently in New Zealand the acceptable daily limit is 40 mg/kg of body weight— for a 60 kg women this is about 13 cans of diet coke per day.

Average exposures in NZ are estimated at 1.69 mg/kg of body weight, with the intakes of high consumers, 3.9 mg/kg of body weight.

Based on the new report, there appears to be no evidence to change the current ADI.

Are Non-Sugar Sweeteners Good for Weight Loss?

The WHO has also recently issued a new guideline in May 2023 stating that non-sugar sweeteners (NSS), which includes aspartame, should NOT be used used as a way of losing weight or reducing the risk of chronic diseases.

This guideline was based on a systematic review and meta-analysis of the available evidence which which suggests that use of NSS does not confer any long-term benefit in reducing body fat in adults or children.

The guideline also suggests that there may be potential undesirable effects from long-term use of NSS, such as an increased risk of obesity, type 2 diabetes, cardiovascular diseases, and mortality in adults.

The new guideline contradicts previous guidelines and recommendations from other reputable organisations, such as the European Food Safety Authority (EFSA), the US Food and Drug Administration (FDA) and the Academy of Nutrition and Dietetics (AND), which have affirmed the safety and usefulness of NSS as part of a balanced diet.

A Critical Eye on the New Guideline

As we navigate the vast and often confusing world of research, it becomes clear that we need to delve a little deeper with a critical eye. There are several issues to consider when interpreting data in this area, including the systematic review.

Firstly, the chicken and the egg scenario — or the causality problem.

Observational data shows that those consuming NSS are more likely to be living with overweight and obesity than non-consumers. But are these individuals using NSS because they are living with overweight and obesity or are NSS causing them to gain weight?

RCTs can be useful in answering these questions, and the WHO report highlights that such studies have shown significantly higher weight loss among those using NSS compared to non-NSS users. This is in contrast to observational prospective cohort studies found higher intakes of NSS were associated with increases in BMI and risk of incident obesity.

Secondly, the issue of confounding needs to be considered.

A cohort study published last year found higher rates of cancer among users compared to non-users. However, these cancers tended to be those associated with obesity. Could obesity be confounding these results?

Interestingly, there was no dose-response relationship in this cohort study. You would expect those who use the most NSS to be at most risk of cancer. That was not the case.

Also, NSS were common not only in soft drinks, but also in many processed foods. This raises the question whether NSS are actually a sign of an unhealthy, highly processed diet.

These are the kind of factors we need to think about carefully when interpreting research findings.

Moreover, it is important to note that the WHO’s new guideline on NSS is not a final or definitive statement on the topic, but rather a conditional recommendation that may require further discussion and adaptation in specific contexts. The WHO also acknowledges that more and better studies are needed to clarify the effects of NSS on human health, and that other factors, such as obesity, diabetes, cardiovascular diseases, and mortality, should also be considered.

Real-world application

The WHO has advised that reducing the sweetness of the diet is a better strategy for improving health, however, the guideline does not provide clear and practical guidance for consumers, health professionals and policymakers on how to do so.

Our takeaway -

• Aspartame is potentially carcinogenic but more and better studies are needed.
• Aspartame at doses commonly consumed is not a concern.
• Diet drinks that use sweeteners instead of sugar are a better option in moderation than sugary drinks.
• And as always, water is a great first choice over other drinks.