WHO’s aspartame and cancer link: a bombshell, or storm in a teacup?

This summer, World Health Organisation scientists dropped a bombshell on the multi-billion global market for zero sugar food and drinks – declaring the leading sweetener aspartame ‘possibly carcinogenic to humans’. But what is aspartame? Which foods and drinks is it used in? And what is the true level of risk to our health? Here, we answer all these questions – as well as assessing the changes food and drinks manufacturers may be forced to take in the wake of the announcement.

When Reuters reported that the World Health Organisation (WHO) was about to label aspartame as ‘possibly carcinogenic to humans’, it was breaking one of the biggest science stories of the year.

In a first public assessment of the widely-used sweetener, WHO’s International Agency for Research on Cancer (IARC) placed it in the third-highest tier – or Group 2B - of its Hazard Classification Rankings. This meant there was ‘limited evidence’ for aspartame causing cancer in humans, as well as ‘sufficient evidence’ of it leading to cancer in experimental animals.

Given that aspartame is a key ingredient in some of the world’s favourite foods and soft drinks, the announcement made global headlines. It also placed a serious question mark over the future use of the sweetener – particularly as IARC said the announcement was “really a call to the research community” for “further studies on the potential association between aspartame exposure and consumer health effects.”

Accidental birth of a bestseller

Aspartame is a methyl ester of a dipeptide consisting of two amino acids:  aspartic acid, and phenylalanine. Somewhere between 160-220 times sweeter than sugarbut with a calorific value of almost zero, it has been successfully marketed as a drinks sweetener under the brand names NutraSweet®, Equal®, and Canderel®. Known to food scientists as food additive E951, aspartame is additionally a key ingredient in around 6,000 food and beverage products around the world – most notably in fizzy drinks but also bestsellers like toothpaste, chewing gum, yogurt and cough medicines. The global value of aspartame as a single ingredient was around US$375 million in 2021, and is expected to grow to around $562 million by 2031 – pretty impressive for a substance discovered by accident.

The chemist James Schlatter chanced upon aspartame in 1965 when he was researching anti-ulcer therapeutics for the drugs firm G.D. Searle and Co. After preparing a mixture of aspartic acid and phenylalanine, Schlatter reportedly licked his finger to turn the page of a book and discovered a pleasantly sweet taste, which the company decided to research. First approved as a sweetener by the US Food and Drug Administration (FDA) in 1974, this permission was briefly put on hold between 1980 and 1981 whilethe FDA investigated and then rejected suggestions of a link between aspartame and brain tumours. During the 1980s, aspartame began to be produced on a large scale, having received approval for use on a wide range of foods, beverages and medicines – including drinks, mints and food toppings. 

So how safe is aspartame?

To many experts, the summer’s headline’s about aspartame are a storm in a teacup – with even IARC stating that there was only ‘limited’ evidence of a link between the chemical and cancer. As a BBC article pointed out, the ‘possibly carcinogenic’ label “frequently causes confusion as it gives no sense of whether the potential risk is big or miniscule”, while aloe vera, pickled Asian vegetables and even working as a hairdresser have the same WHO risk classification. The BBC also quoted WHO director of nutrition and food safety, Dr Francesco Branca, as saying the announcement had merely “raised the flag” that aspartame may not be good for consumers – adding that occasional users of diet drinks or other products containing aspartame “shouldn’t have a concern.” Cambridge University statistics expert Professor Sir David Spiegelhalter said IARC reports on carcinogens were “getting a bit farcical”, given the lack of evidence of substantial risk. “As they have said for 40 years, average people are safe to drink up to 14 cans of diet drink a day, which is about …. half a large bucketful,” he said. The FDA also strongly disagreed with IARC, saying: “Aspartame is one of the most studied food additives in the human food supply. FDA scientists do not have safety concerns when aspartame is used under the approved conditions”. It also noted that Health Canada and the European Food Safety Authority “had both evaluated the sweetener and consider it safe at current permitted levels.” However, on the other side of the argument, the World Cancer Research Fund International strongly supported IARC’s call for “well-conducted studies to better understand the relationship between aspartame and cancer risk and for more experimental studies to explore potential biological pathways.”

Aspartame alternatives

Given that aspartame underpins multi-billion dollar global industries such as zero sugar beverages, manufacturers will be reluctant to reformulate their winning formulas on the basis of the IARC announcement. Concerns about obesity and diabetes are fuelling fast growth in no-sugar beverages, with the sector expected to be worth around US$ 13 billion globally by 2033. In countries like the UK, around half of carbonated drinks on supermarket shelves already contain aspartame, with sugar now used in less than a third of such products.

According to foodmanufacture.co.uk, Coca-Cola and PepsiCo do not intend to alter the recipe of their aspartame-containing soft drinks, but industry analysts have argued that the situation may change if customers stop buying those products in significant numbers, or if researchers find new and worrying evidence of a link between aspartame and cancer.

“The headlines could have a negative impact on sales volumes of lower-calorie sodas, which is really a function of how much attention the story garners," Garrett Nelson, senior equity analyst at CFRA Research, told Reuters.

"We think this report is likely to cause beverage companies and trade groups both to challenge the findings and swap to substitute sweeteners in their recipes.”

Among the leading candidates to replace aspartame is stevia rebaudiana – a member of the sunflower family which is up to 300 times sweeter than sugar and already being used in many low-calorie food and drink products.

Another potential successor is swingle fruit extract or SGFE – comprised of intensely sweet extracts of the Monk Fruit known as mogrosides. Since Monk Fruit has been consumed in China for several hundred years and used as a herbal medicine for decades, SGFE’s safety profile is considered to be good – and like stevia, it has been approved by the FDA.

Another FDA-sanctioned sweetener that we may see more of in future is thaumatin – a low-calorie product extracted from the fruit of the West African plant Thaumatococcus daniellii, and described in James N. BeMiller’s Carbohydrate Chemistry for Food Scientists as “totally natural with an intense sweetness.”

“Thaumatin has a wide range of applications in food and drinks,” BeMiller adds, “and is particularly effective for its flavoring properties and because it adds mouth feel.”