Is aspartame bad for you? What doctors want you to know as the sweetener is declared a "possible carcinogen" by WHO

As the World Health Organization (WHO) declares aspartame a "possible carcinogen", we spoke to doctors to find out just how concerned we should be

Illustration of aspartame sitting on metal spoon
(Image credit: Getty Images)

Aspartame has dominated headlines over the past month with concerns that the sweetener could be directly linked to cancer. However, while it's important to keep an open mind when it comes to developing scientific research, doctors are urging people not to worry. Here, we explain exactly why. 

If you had never heard of the artificial sweetener aspartame until recently, you're not alone. Aspartame is commonly used as a sugar substitute in lots of the food and drink items you might find on a supermarket shelf, but unless you regularly read the ingredients list of every single canned drink and packaged food you consume, you may not be familiar with it until now. 

Aspartame was propelled into the headline a few weeks ago as many outlets reported that the World Health Organization (WHO) was considering declaring the artificial sweetener a "possible carcinogen", which means there's limited evidence, with more research required, to suggest continuous consumption of the ingredient could lead to cancer. This has since been confirmed by the health body - with the clause that aspartame remains safe to consume within the recommended limit. 

The announcement on July 13 and the news cycle leading up to it naturally caused concern since aspartame is used in many popular food and drink items, such as diet sodas, including Diet Coke, Diet Pepsi, and some Lucozade drinks, as well as chewing gum and other sweet products such as Müller Light yogurt and frozen desserts. 

While this all sounds very worrying, there is still no extensive evidence yet found to prove there is a surefire link between aspartame and cancer, with the FDA (the U.S. Food & Drug Administration) also confirming earlier in May this year that aspartame was "safe for the general population." 

So where have these fresh concerns around aspartame come from and how worried should we be? We spoke to several doctors, dieticians, and pharmaceutical experts to try and get to the bottom of what the latest WHO warning could mean for us and how it might change our eating and drinking habits. 

What is the current controversy with aspartame?

Following a report by The International Agency for Research on Cancer (IARC) - the cancer research arm of WHO - on the safety of the sweetener, aspartame is now classified as a possible carcinogen. However, officials have also confirmed it's safe to continue consuming within the recommended daily limit. 

This daily limit, which is set by another group within the organization - the Joint Expert Committee on Food Additives (JECFA) - has also not been changed and currently sits at 40 milligrams per kilogram of body weight every day. For an adult weighing 154 pounds (69kg), that's up to 14 cans of Diet Coke. 

The report that triggered the new classification was based on a review of three different human studies from the US and Europe that found a possible link between aspartame and a type of liver cancer called hepatocellular carcinoma. 

"While safety is not a major concern at the doses which are commonly used, potential effects have been described that need to be investigated," WHO's Dr Francesco Branca says. 

Concerns around aspartame are nothing new though. A quick internet search will bring up decades of reports (such as studies from the University of Washington and Georgetown University), linking it to headaches, dizziness, and cancer-causing properties. During Brexit negotiations, some food safety experts even tried to have the sweetener banned in the UK. However, aspartame remains one of the most well-researched food additives around and it has been approved for use by regulatory bodies around the world time and time again.

Aspartame has been put in Group 2B of the IARC's list of carcinogens. There are three groups in total: Group 1 ("carcinogenic to humans"), Group 2A ("probably carcinogenic to humans"), Group 2B ("possibly carcinogenic to humans"), and Group 3 ("not classifiable"). 

Group 2B is the organization's second-lowest risk classification, with substances on this list just meeting the minimum requirements to "possibly" be capable of causing cancer but without extensive evidence available, as noted. 

Also featured in the same category are engine fumes, diesel fuel, aloe vera, and pickled vegetables, and because of this, it's likely to cause controversy if the IARC does put aspartame in this group. The organization has been criticized before for causing panic after putting popular products and substances that are hard to avoid - like red meat and the electromagnetic fields emitted from mobile phones - on their lists.

Is aspartame banned in the UK or US?

No, aspartame is currently approved for use in the US, UK, and every country in the world. The FDA confirmed this year that they'd "reviewed more than 100 studies designed to identify possible toxic effects" of the product and deemed it "safe for the general population", while the NHS has confirmed that all sweeteners in the UK undergo "rigorous safety assessment before they can be used in food and drink". 

For this to change, physician Dr Crystal Wyllie explains, the report being released on July 14 will have to show that aspartame meets the criteria of being a possible carcinogen. I.e. It has to "cause or promote changes in the DNA of cells," she explains. "These changes can lead to uncontrolled growth and the creation of tumors", which can be cancerous. 

What products have aspartame in?

Aspartame is found in as many as 6,000 food and drink products around the world, but some of the most common include: 

  • Diet soda, including Diet Coke, Diet Pepsi, and Crystal Light
  • Chewing gum, like Trident, Extra, and Orbit
  • Gelatin, which is used in some pre-packaged desserts like jellies, marshmallows, and candy corn
  • Breakfast cereal 
  • Yogurts, including Müller Light and Dannon Light & Fit
  • Sugar-free cocoa mix 
  • Medications, such as cough drops and gummy vitamins 
  • Artificial table sweeteners 

While cakes and baked goods often get a bad name in the world of healthy eating, this is one place where you won't find aspartame since the sweetener contains amino acids that aren't stable enough to fully survive the baking process. 

Bowl of colorful cereal loops

Many low-sugar and low-calorie cereals include aspartame as a sweetener. 

(Image credit: Getty Images)

What are the other names for aspartame?

Many traditional tabletop sweeteners contain aspartame, with some of the most popular brand names including Nutrasweet, Equal, and Sugar Twin.

These low- and zero-calorie sweeteners use aspartame because it's about 200 times sweeter than sugar, which means you need a lot less to sweeten your drink. When it comes to calories, 1 gram of aspartame has 4 calories and to get the same level of sweetness, you'd need 8 grams of sugar at 32 calories. In terms of calories and sugar intake, it makes a big difference and explains why a standard 12oz can of Diet Coke only contains 7 calories and the same can of original Coca-Cola contains 132 calories. 

So how worried should we be about aspartame and what do doctors say?

Given the most recent news, it’s totally understandable to think that this is the final straw and we need to cut the sweetener out of our diets completely - but that's not the case. 

"While there are some very serious potential risks associated with aspartame, the sweetener has been approved as safe by the FDA and is also approved by the NHS in the UK, having undergone significant testing for a long period of time," confirms chief pharmacist Jana Abelovska. "Further research into the health implications of aspartame is still being carried out, but there is no need to immediately panic and stop using the sweetener altogether."

Importantly also, the IARC (who may list aspartame as "possibly" a carcinogen) doesn’t take into account how much of the substance you’d need to consume to have a damaging effect. This advice comes from the JECFA alongside external regulators and it has remained the same even now the report's findings have been announced. 

It’s concerning that so many popular items contain potentially-carcinogenic properties but per the daily limits, given by JECFA, you'd have to drink more than 14 individual cans of Diet Coke a day to actually face any serious risk from aspartame. 

"Group 2B, “possibly carcinogenic to humans”, is used where the evidence of potential carcinogenicity in humans is ‘limited’, and the evidence in experimental animals is ‘less than sufficient’, in the IARC’s words," says Professor Kevin McConway, emeritus professor of applied statistics at the Open University. "So there could remain considerable doubt that something in this group could ever, under any circumstances, cause cancer in humans. There is a group below that, group 3, “not classifiable as to its carcinogenicity in humans” where the evidence of a hazard is so weak that the IARC experts don’t regard it as at all adequate. The evidence for group 2B exposure is a bit stronger than that, but could still be really pretty weak."

Person pouring cola into class, sitting at restaurant table in the sun

(Image credit: Getty Images)

These groups are based on the strength of the evidence that a substance could cause cancer, rather than how dangerous something really is. There is a lot of evidence on aspartame as noted by the FDA and if there was immense convincing evidence that the sweeter was a seriously worrying cause of cancer, it would be in a higher group like Group 2A ("probably carcinogenic to humans") or Group 1 ("carcinogenic to humans"). 

Products we know have an actual link to cancer - such as excessive amounts of red meat, alcohol, smoking, and second-hand smoke, are just some of those that fit into groups classed as a higher risk by the IARC. Even certain kinds of professions, such as being a hairdresser (thanks to exposure to certain chemicals) and doing shift work (which often disrupts healthy sleep patterns) carry a higher risk of potentially causing cancer than aspartame, really highlighting just how low the direct threat of cancer here is.

Even then, "the dose makes the poison," says Professor Oliver Jones, professor of chemistry at RMIT University in Melbourne. "For example, 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 secondhand smoke." In the same way, it's very unlikely that having a Diet Coke occasionally isn't going to make any difference to your health. 

While many of the experts woman&home spoke to for this article are largely unconcerned by the news, they warn that this is still an unfolding story so we should keep an open mind. “I believe it’s critical for all of us - medical professionals, food scientists, and the public - to keep an open mind, stay informed, and be ready to adapt based on reliable scientific evidence,” says physician Dr Kelvin Fernandez.

Chief dietitian Dr Caitlin Hall agrees. "It's important for individuals to stay informed and make decisions based on comprehensive guidance from multiple sources," she says. "While awaiting further updates, it's advisable to opt for natural alternatives to artificial sweeteners whenever possible and prioritize a balanced diet that includes a variety of fresh and whole foods."

With the above in mind though, are there other health risks and worries linked to aspartame? While it’s “potentially carcinogenic” effect has been established and revealed by the experts to be not much to worry about, doctors do want to warn about other side effects to watch out for.  

  • Adverse gut health: "Studies have demonstrated that artificial sweeteners can cause changes in the composition and diversity of the gut microbiome," says Dr Hall, who is also the head of clinical research at myota. "These alterations can disrupt the delicate balance of beneficial bacteria, potentially leading to issues such as bloating and digestive discomfort."
  • Weight gain: “Some studies have found that artificial sweeteners, including aspartame, may actually lead to an increase in weight, rather than their intended purpose of helping to avoid weight gain," says Abelovska, who is also the chief superintendent pharmacist at Click Pharmacy.
  • General discomfort: "I've come across patients who've experienced discomfort with artificial sweeteners, including aspartame," says Dr Fernandez, who is also a healthcare educator at Ace Med Boards. "These cases, while not indicative of a broader trend, do highlight the importance of individual differences in how our bodies react to different substances."

Just as many ditched their cookware after questions about are non-stick pans safe arose last year, you may be looking to cut out or scale back on products with aspartame in your diet. If so, Dr Fernandez suggests doing it slowly. "It might be a smoother ride for your body if you do it step-by-step rather than going cold turkey," he suggests. "For instance, if you're sipping three diet sodas a day, trying scaling it back to two, then one, and so on."

Grace Walsh
Health Channel Editor

Grace Walsh is woman&home's Health Channel Editor, working across the areas of fitness, nutrition, sleep, mental health, relationships, and sex. She is also a qualified fitness instructor. In 2024, she will be taking on her second marathon in Rome, cycling from Manchester to London (350km) for charity, and qualifying as a certified personal trainer and nutrition coach. 

A digital journalist with over six years experience as a writer and editor for UK publications, Grace has covered (almost) everything in the world of health and wellbeing with bylines in Cosmopolitan, Red, The i Paper, GoodtoKnow, and more.