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Diet soda is a widely consumed product that contains the artificial sweetener aspartame. Krit of Studio OMG/Getty Images
  • World Health Organization (WHO) officials declared aspartame a potential carcinogen on July 14.
  • Aspartame is a common artificial sweetener ingredient in diet sodas, chewing gum, and other products.
  • Despite the health risks, the WHO noted there’s “limited evidence” that aspartame can cause cancer and listed the sweetener as a Class 2B carcinogen.

A common artificial sweetener in everything from diet sodas to chewing gum has been labeled a possible carcinogen by one of the world’s leading health agencies.

On July 14, the World Health Organization’s International Agency for Research on Cancer (IARC) declared aspartame “possibly carcinogenic to humans” for the first time.

However, agency officials said there was only “limited evidence” that aspartame can cause human cancer, so it was listing the sweetener as an IARC Group 2B carcinogen. Substances in that category are described as “possibly carcinogenic to humans.”

The WHO’s Joint Expert Committee on Food Additives (JECFA) reaffirmed the acceptable daily limit of aspartame at 40 milligrams for every kilogram of body weight.

Dr. Francesco Branca, director of the Department of Nutrition and Food Safety at WHO, said in a joint news release:

“Cancer is one of the leading causes of death globally. Every year, one in six people die from cancer. Science is continuously expanding to assess the possible initiating or facilitating factors of cancer, in the hope of reducing these numbers and the human toll. The assessments of aspartame have indicated that, while safety is not a major concern at the doses which are commonly used, potential effects have been described that need to be investigated by more and better studies.”

Aspartame is an artificial sweetener widely used in various food and beverage products since the 1980s. Products containing aspartame may include:

  • diet drinks
  • chewing gum
  • gelatin
  • ice cream
  • dairy products (i.e., yogurt)
  • breakfast cereal
  • toothpaste
  • over-the-counter medications (i.e., cough drops, chewable vitamins)

The Food and Drug Administration (FDA) took issue with the WHO’s new classification of aspartame.

“Aspartame being labeled by IARC as ‘possibly carcinogenic to humans’ does not mean that aspartame is actually linked to cancer,” FDA officials said in a statement.

“FDA scientists reviewed the scientific information included in IARC’s review in 2021 when it was first made available and identified significant shortcomings in the studies on which IARC relied,” FDA officials added. “We note that JECFA did not raise safety concerns for aspartame under the current levels of use and did not change the Acceptable Daily Intake (ADI).”

The WHO’s announcement also conflicts with major food manufacturers who widely use aspartame, mostly as a sugar substitute.

Similar past IARC rulings have raised consumer concerns, led to lawsuits, and pressured manufacturers into scrambling for alternative ingredients.

Since 1981, WHO regulators have said aspartame is safe within accepted daily limits. An adult weighing 60 kg (132 pounds) would have to drink 12 to 36 cans of diet soda — depending on the amount of aspartame in the beverage —daily to be at risk, according to Reuters.

Other regulatory bodies, including those in the United States and Europe, have shared that opinion.

Aspartame has been extensively studied for years.

In 2022, a study in France among 100,000 adults concluded that people consuming larger amounts of artificial sweeteners — including aspartame — had a slightly higher risk of cancer.

An early 2000s study by the Ramazzini Institute in Italy reported some cancers in mice and rats were linked to aspartame.

However, the first study could not prove that aspartame caused the increased cancer risk and questions have been raised about the methodology of the second study.

The IARC has four levels of classification. Each level is based on the strength of the evidence, not specifically on how dangerous a substance is:

  1. carcinogenic
  2. probably carcinogenic
  3. possibly carcinogenic
  4. not classifiable

Dr. Misagh Karimi, an oncologist in gastrointestinal cancers at City of Hope Orange County Lennar Foundation Cancer Center in California, told Medical News Today it’s important to understand when a product falls into one of the IARC’s four categories.

“While it can be confusing and distressing to hear of this news around aspartame, it is essential to understand that the IARC does not consider the scale of risk of these carcinogens and a Class 2B carcinogen does not equate to a definite or even possible cause of cancer,” Karimi said.

“To put it simply, a Class 2B classification, which aloe vera and nickel are included under as well, means there are a few suggestions and small evidence leading researchers to believe that aspartame could possibly cause cancer.”

– Dr. Misagh Karimi, oncologist

In the past, products from processed meat, to asbestos, to electromagnetic fields associated with cell phones have been, at one time or another, classified as possible carcinogens, depending on use.

Similarly, the health risks of aspartame may depend on how much is consumed and how often.

Melanie Murphy Richter, a registered dietician nutritionist and an instructor in the University of California Irvine’s Nursing Department, told MNT that aspartame is found in more than 6,000 food products and is “leaned on” by scores of people for diabetes and weight management.

“There is balance in everything when it comes to food and health,” Richter said.

“The [Food and Drug Administration] has approved the consumption of aspartame at 50mg per kg of body weight [per day], which is quite high. For example, if you are 130 pounds, you could, according to the FDA, consume upward of 3,200 mg of aspartame a day, which is equivalent to over 15 cans of diet soda,” Richter added.

Richter noted most people consume aspartame at much lower rates. Which still doesn’t address how much is too much.

“Based on the science, right now it’s unclear as to what a reasonable amount could safely be since the FDA’s approval is well above the average daily consumption,” she said.

Dr. Srini Hejeebu, an internal medicine specialist at the University of Toledo Medical Center in Ohio, told MNT it would be difficult for people to transition to other forms of supplements.

“Three-quarters of all diet sodas, sugar-free foods and sugar-free candies have some form of aspartame in them,” Hejeebu said.

“The biggest problem with these artificial sweeteners is that when people think what they’re eating or drinking is ‘diet,’ they consume more than they should. Although the studies are not conclusive, consumption of diet sodas has been linked to worsening diabetes and obesity. A lot of the time we do not even realize there is an artificial sweetener in the product we’re buying.”

– Dr. Srini Hejeebu, internal medicine specialist

Dr. Jessica Jones, an oncologist with UTHealth Houston and Memorial Hermann, told MNT that the connection between aspartame in diet soda and cancer remains unclear. Still, Dr. Jones offered some advice for those who want to ensure their beverage isn’t increasing their risk of getting cancer.

“Consider ditching soda entirely and moving to water or tea,” Dr. Jones said.

Matthew Landry, PhD, an assistant professor of population health and disease prevention at the University of California Irvine, noted that aspartame isn’t just in diet soda.

“We can also find it in chewing gum, frozen desserts, yogurt, dessert mixes. It’s sometimes even used in vitamins, supplements, and cough drops,” Landry told MNT.

That doesn’t mean you can’t find alternatives, he added.

“First is knowing what to look for in the grocery store. Aspartame is going to most likely appear in processed foods. If you see either the word ‘aspartame’ or ‘phenylalanine’ then the product contains aspartame,” Landry said.

Dr. Landry noted that anything labeled “diet” or “sugar-free” likely contains aspartame.

“When in doubt, choose foods that are unprocessed — whole fruits and vegetables have no artificial sweeteners or aspartame and have a host of other health benefits like fiber. When you do need to sweeten up a beverage or food, consider honey or maple syrup.”

– Matthew Landry, PhD, assistant professor of population health and disease prevention

Dr. Hejeebu noted other natural sweeteners that may offer an alternative to aspartame. These include:

“These [sweeteners] may be a little bit better, but we cannot say for sure because we will need to do future studies,” Dr. Hejeebu said.