IE 11 is not supported. For an optimal experience visit our site on another browser.

Aspartame is a possible carcinogen, WHO says. Should you stop drinking diet soda?

WHO has declared aspartame, a popular artificial sweetener, a possible carcinogen. Should you ditch diet soda?
/ Source: TODAY

The World Health Organization’s cancer research agency, the International Agency for Research on Cancer, has declared the artificial sweetener aspartame a possible carcinogen. The organization released a statement and summary of its findings regarding the decision on July 13.

“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," Dr. Francesco Branca, director of WHO's department of nutrition and food safety, said in a press release. 

The press release continued: "IARC’s hazard identifications are the first fundamental step to understand the carcinogenicity of an agent by identifying its specific properties and its potential to cause ... cancer."

The U.S. Food and Drug Administration, however, disagreed with WHO's categorization of aspartame as a possible carcinogen.

"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,” the FDA said in a statement to NBC News.

Despite the IARC's conclusion that aspartame may be a carcinogen, another agency within WHO, the Joint Expert Committee on Food Additives, said on July 13 it would not to make any changes to its guideline of how much aspartame a person can safely consume.

Numerous industry organizations told NBC News they supported the JECFA's decision and criticized the IARC'S.

In a statement to NBC News, American Beverage stated that “IARC is not a food safety agency" and stressed that its products' safety is of the utmost importance. “This strong conclusion reinforces the position of the FDA and food safety agencies from more than 90 countries,” American Beverage CEO Kevin Keane said of JECFA's decision not to change aspartame consumption guidelines.

The Calorie Control Council, representing low- and reduced-calorie food and beverage makers, also praised the JECFA while calling the IARC's conclusion “wrong” and “potentially damaging.” 

Multiple experts tell that IARC's classification of aspartame as a possible carcinogen isn’t as scary as it may seem and that, even though such information is important for consumers to have, there are several factors to consider before dumping diet sodas altogether.

What is a carcinogen?

A carcinogen refers to anything that's capable of causing cancer, such as a substance, organism or another agent, according to the National Institutes of Health. Carcinogens can be a natural part of the environment, like ultraviolet rays from the sun, which can cause skin cancer, or humans may create them, like cigarette smoke or car exhaust. Carcinogens usually cause cancer by mutating cells' DNA.

Is aspartame a carcinogen?

The IARC has classified aspartame as a "possible" carcinogen. It did so based on three human studies that found drinking artificially sweetened drinks may increase the risk of a common type of liver cancer. Studies in mice and rats who ate food with aspartame also found some increased rates of tumors, but these studies were flawed, according to the IARC.

The FDA also said its scientists had reviewed these studies and "identified significant shortcomings," according to NBC News.

The chief scientific officer of the American Cancer Society, Dr. William Dahut, told NBC News in a statement that the research into aspartame's possible cancer causing properties is evolving.

The move to classify aspartame as possibly carcinogenic means the agency is saying that, based on all the available evidence, the sweetener could cause cancer — though the agency didn't say how likely it is, and it noted that the evidence in humans is "limited."

"IARC classifications reflect the strength of scientific evidence as to whether an agent can cause cancer in humans, but they do not reflect the risk of developing cancer at a given exposure level," WHO's July 13 press release explained.

The agency has four categories for classifying the cancer risk of certain foods, chemicals and goods. Those are 1, 2a, 2b and 3. Class 1 means the item can cause cancer; class 2a means it probably does; class 2b means it possibly does; and class 3 means it carries no cancer risk. The agency has declared aspartame a class 2b carcinogen, which places it alongside aloe vera, dry cleaning and pickled vegetables, per the IARC website

It’s also worth noting that the IARC categories do not address the magnitude of risk — for example, alcoholic beverages and plutonium, a radioactive metal, are both considered class 1 carcinogens. What’s more, “while developing cancer is certainly scary, not all carcinogens are necessarily dangerous in reasonable amounts — think sunlight, for example,” Tara Schmidt, lead registered dietitian for the Mayo Clinic Diet, tells

The FDA and numerous industry trade groups have said that aspartame is safe to consume (within certain limitations) since the IARC’s ruling came out.

What is aspartame made of?

Aspartame, an artificial sweetener approved by the U.S. Food and Drug Administration in 1981, is made of two amino acids, aspartic acid and phenylalanine, according to the FDA. Its full name is L-aspartyl-L-phenylalanine methyl ester.

It's designed to “provide sweetness not usually found naturally in foods,” Dr. Donald Hensrud, professor of nutrition and preventive medicine at Mayo Clinic College of Medicine, tells 

What products contain aspartame?

Aspartame is a critical ingredient in diet sodas like Diet Coke and Diet Pepsi, and other diet drinks like Crystal Light. Aspartame is also found in sugar-free chewing gums and food products, like sugar-free Jell-O. It’s also popular in packet form and is commonly used to sweeten coffee and tea. Aspartame is sold under the brand names Nutrasweet, Equal and Sugar Twin, according to the FDA.

Other types of products that may contain aspartame, per the IARC, include: ice cream; dairy products, such as yogurt; breakfast cereal, toothpaste; and medications, such as cough drops and chewable vitamins.

Aspartame products tend to be lower in calories than their sugar-based counterparts.

How much aspartame is in diet soda?

Worried that the IARC's announcement means you'll have to ditch your favorite diet soda? Diet Coke and other products don't actually contain that much aspartame, the experts explain.

Because aspartame is about 200 times sweeter than sugar, the amount of aspartame needed to sweeten one 12-ounce can of diet soda is very small — only about 192 milligrams, or 0.007 ounces.

How much aspartame is too much?

Since the IARC's ruling, neither the JECFA nor the the FDA have changed their guidelines on how much aspartame is safe to consume.

“The FDA has established an acceptable daily intake for aspartame at 50 milligrams per kilogram of body weight per day,” Jen Messer, lead registered dietitian at Jen Messer Nutrition, tells “This means that a person weighing 150 pounds would still fall within an acceptable daily intake by consuming about 17 12-ounce cans of diet soda per day.”

In a statement, the JECFA reaffirmed its guideline that it's safe to consume 0 to 40 milligrams of aspartame per kilogram of body weight per day. "With a can of diet soft drink containing 200 or 300 mg of aspartame, an adult weighing (154 pounds) would need to consume more than 9–14 cans per day to exceed the acceptable daily intake, assuming no other intake from other food sources," the press release explained. That's also about 75 packets of aspartame sweetener a day for some who weights 130 pounds.

How worried should you be?

Experts caution that WHO categorizing aspartame as a possible carcinogen is not cause to worry, as the guidelines for safe consumption have not actually changed.

"This is not meant to have people throw away their diet soda and their chewing gum," Dr. Tara Narula, a cardiologist with Northwell Health said on TODAY on July 14. "It's meant to raise awareness that we need research. It's meant to make people pause and be mindful about how they're consuming things."

"If you're using (aspartame) in a moderate way and not drinking 30 diet sodas a day, you're probably fine," she continued. "The point is about a healthy palette of eating throughout the day. And what we don't want to do is push people the other way to sugar. As a cardiologist, we talk about limiting added sugar."

Dahut echoed this idea in a statement to NBC News: “We recommend people use (the) report by IARC as a time to reflect on their use of aspartame, but also an opportunity to review their overall dietary intake, including processed meat and alcohol, known carcinogens associated with increased risk of cancer."

Even if you're on the higher end of aspartame consumption, you're still likely only getting about 30 milligrams per kilogram of body weight per day, according to WHO estimates, which is less than the JECFA's maximum of 40 milligrams. And the average person's aspartame consumption is 10 times less than the acceptable daily limit, according to WHO.

Of course, drinking several cans of diet soda isn't recommended, and Hensrud says “that even low-level consumption (of aspartame) over a long period of time may have adverse health effects, but ... the exact level of risk can be difficult to determine, and this uncertainty is where the confusion is.”

Dr. Neil Iyengar, a medical oncologist at the Memorial Sloan Kettering Cancer Center, also told NBC News that people with an increased risk of some cancers due to their genetics may benefit from this information if they want to do everything they can to lower their risk.

“This is information they would want,” he said. 

Is diet soda better than regular soda?

Given that diet soda often contains aspartame, which may increase a person's risk of cancer, is it better to drink regular soda if you're craving a sweet, bubbly beverage?

Unfortunately, there's no a simple answer, as both diet soda and regular soda are "associated with risks,” says Hensrud. 

Adds Schmidt: “It’s important to not draw the conclusion that regular soda is now superior to diet. It’s clear that regular and diet soda are both low in nutrient-density.”

And when weighing potential risks associated with either type, remember that regular, high-calorie soda can increase risk of obesity, which, in turn, increases cancer risk. “We’ve got plenty of research linking obesity and poor diet to cancer risk,” says Schmidt.

Can diabetics drink diet soda? 

Diet soda is frequently used as a substitute for regular soda by people with Type 2 diabetes because “choosing diet soda can help satisfy your craving for soda without causing a rise in your blood sugar levels,” explains Messer.

Even still, some research shows that “even individuals with Type 2 diabetes need to be cautious and mindful of the amount of diet soda and other diet foods they eat and drink,” says Dr. Uma Naidoo, director of nutritional and lifestyle psychiatry at Massachusetts General Hospital and author of “This Is Your Brain on Food.”

Is diet soda bad for you?

Because the IARC only put aspartame in the “possibly” causes cancer category, and because “there are currently no studies that show that aspartame causes cancer in humans,” says Messer, one’s risk of getting cancer by drinking diet soda remains very low, if it exists at all. Again, neither the JECFA and FDA have changed their guidelines for how much aspartame is safe to consume.

And there may be potential upsides of drinking diet soda to consider for some people. “Replacing sugary beverages with low- or no-calorie drinks can be beneficial for overall health,” says Messer. “They can also be a helpful way for individuals to transition from a high intake of sugar-sweetened sodas to more healthy alternatives.” 

Eventually, that could mean ditching both regular and diet soda altogether and drinking water alone — an ideal you could shoot for, Naidoo says.

“While an occasional diet soda is probably OK, relying on either diet soda or regular soda is likely not a good idea for your overall health,” she says. “It’s important that people don’t panic at this announcement but use this information to make an informed choice about any food or beverages they are consuming that contains aspartame.”