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Aspartame — when is sweet enough?

In this article, we examine the prevalence of and risks of aspartame and consider whether such worry is well founded and should manufacturers act?

The recent addition by the World Health Organisation (WHO) of aspartame to a list of substances believed to be potentially carcinogenic has sparked consternation amongst consumers, manufacturers and product liability insurers. We examine the prevalence of and risks of aspartame and consider whether such worry is well-founded.

What is aspartame? 

In brief, aspartame is an artificial sweetener which contains a combination of two amino acids, phenylalanine and aspartic, joined by a peptide bond. It is approximately 200 times sweeter than sugar, meaning that only a small amount is needed to match the sweetness of sugar.

Its use is widespread by food manufacturers and it is found in diet or sugar free versions of over 6,000 products – commonly food and drinks. This includes well-known brands such as “Diet Coke” and “Pepsi Max”, but aspartame is also added to some “full sugar” products. The health risk from aspartame is believed to arise from the way in which it is processed by the body - some of which is broken down into methanol – a substance considered to be toxic in large quantities.

The WHO recommendation  

The body recommending the addition of aspartame is the International Agency for Research on Cancer (IARC) which is a semi-autonomous arm of WHO. It divides the risk of causing cancer into 4 categories; firstly, those which definitively do cause cancer – for example, tobacco, alcohol and radiation. Secondly, those substances which “probably do cause cancer” – for example vinyl fluoride, ‘red meat’ or creosotes. Thirdly, those which potentially cause cancer which now includes aspartame alongside diesel exhaust fumes and coffee. The fourth category applies to substances where there is no “current” evidence that it causes cancer.

The recommendation to include aspartame follows the publication of three animal studies showing a possible connection to liver cancer and concerns over the chemical properties of aspartame possibly linked to cancer. However, the studies according to two experts have been unconvincing.

Dr Mary Schubauer-Berigan from the International Agency for Research on Cancer (IARC) itself, (BBC news online) stated that:

“The evidence is not of sufficiently high quality or convincing enough”.

Paul Pharoah, Professor of Cancer Epidemiology at Cedars-Sinai Medicine Centre Los Angeles (The Times, 14 July 2023), stated that:

“The evidence that aspartame causes primary liver cancer or any other cancer in humans is weak”.

Should we be worried? 

Initial concern amongst consumers was perhaps understandable given the proliferation of aspartame in diet and sugar free food and beverage products. It would have been helpful however if the IARC’s recommendation had been placed in the context afforded by the commentary provided several days later by a separate arm of the World Health Organisation – the Joint Food and Agriculture Organisation/WHO Expert Committee on Food Additives. This branch of WHO considers the evidence of harm and the level of risk – in short, how much a person would need to consume for aspartame to be a risk to health, not whether it is potentially carcinogenic per se.

Their guidance remains unchanged despite the IARC’s recommendation, namely that 40 mg of aspartame per kilogram of body weight remains “safe”.

Each can of diet or sugar free drink contains broadly 200 mg of aspartame. A person weighing 70 kg could therefore safely consume 14 cans each day, whilst for a heavier person weighing 85 kg, the safe limit would be 17 cans each day. For a lighter person (for example a child), weighing 30 kg, the safe limit would be six cans a day.

The overall risk to consumers of aspartame is best summarised by Dr Francesco Branca, Director of Nutrition and Food Safety (WHO) as reported by “News online”, “the problem is for high consumers”.

Should manufacturers act?

Previous product liability litigation has shown the importance the courts place upon manufacturers providing end consumers with nutritional and relevant safety information to enable them to make informed decisions.  

The current consensus of medical opinion is, firstly, that the evidence base to show a definitive causal link to liver cancer has not been established and secondly, that any potential risk “kicks in” only by consuming very high quantities of diet or sugar free products containing aspartame.

In this context, manufacturers are likely to take the view that placing warnings on products currently manufactured is both premature and unnecessary. We suspect that the courts in the UK would take a similar view. In the event that a claim is pursued against a product manufacturer, a claimant would also have grave difficulty in establishing both medical and legal causation given the current epidemiological limitations.


With the current concentration on the risks associated with processed and ultra processed food, it is unsurprising that the WHO’s recent announcement has provoked much in the way of media coverage. 

Context is, however, vital – the evidence suggests that unless you are consuming industrial quantities of diet or sugar free drinks on a daily basis, there is very little to spark concern.

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