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Is aspartame safe?
The World Health Organization’s cancer research group on Thursday said that it was categorizing the common artificial sweetener found in Diet Coke and other sugar-free foods and drinks as a possible carcinogen, but the agency's food safety group said that the evidence wasn't convincing and that the compound could still be consumed safely in fairly high amounts.
The U.S. Food and Drug Administration said it did not agree that aspartame should be categorized 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.
Aspartame is sold under the names Equal, Nutrasweet and Sugar Twin. It’s found in many diet sodas, as well as some chewing gums and sugar-free, low-calorie desserts.
During a media briefing on Wednesday ahead of the announcement, WHO officials stressed that they were not advising companies to withdraw products or telling people to avoid aspartame altogether.
“We’re just advising for a bit of moderation,” said Dr. Francesco Branca, the director of the WHO’s Department of Nutrition and Food Safety.
The seemingly conflicting statements from the WHO — that aspartame may possibly cause cancer but is safe to consume — came from two separate groups within the organization.
One group, the International Agency for Research on Cancer (IARC), focuses on identifying cancer-causing agents. The other, the Joint FAO/WHO Expert Committee on Food Additives, looks at the safety of food additives and whether they pose a risk to consumers. The groups undertook the review after an advisory panel marked the compound a “high priority” for review in 2019.
The IARC said in a release Thursday that it was classifying aspartame as possibly carcinogenic, meaning there is some evidence that it may cause cancer in humans, but that the evidence is far from conclusive, according to Mary Schubauer-Berigan, the acting head of the IARC Monographs program. (Exposure to a carcinogen does not mean a person will get cancer.)
Given the limited evidence, the Expert Committee on Food Additives concluded that it is currently not making any changes to the recommended limit of aspartame that a person can safely consume.
That limit — known as the acceptable daily intake — is quite high: 40 milligrams per kilogram of body weight per day, or 40 milligrams per every 2.2 pounds a person weighs.
That means an adult who weighs 154 pounds, or 70 kilograms, would need to consume more than nine to 14 cans of diet soda per day to exceed the acceptable daily intake, assuming they aren’t getting aspartame from other foods or drinks. A 12-ounce can of diet soda typically contains 200 to 300 milligrams aspartame.
The FDA’s limit is even higher, at 50 milligrams per kilogram a day, or 50 milligrams per 2.2 pounds of body weight.
The Coca-Cola Company did not respond to a request for comment. In a statement, American Beverage, the industry trade group, said that the safety of its products is its highest priority and that the “IARC is not a food safety agency.”
American Beverage praised the Expert Committee on Food Additives’ decision to not make changes to the daily acceptable limits of aspartame.
“This strong conclusion reinforces the position of the FDA and food safety agencies from more than 90 countries,” American Beverage CEO Kevin Keane said in a statement.
The Calorie Control Council, which represents the low and reduced calorie food and beverage industry, similarly praised the Expert Committee on Food Additives while blasting the IARC ruling as “wrong” and “potentially damaging.”
The International Agency for Cancer Research looks at whether certain compounds, organisms or agents are carcinogenic.
It classifies its findings into four groups: Group 1 substances “cause cancer.” These include tobacco smoke and UV rays from the sun. Group 2a substances are “probable carcinogens,” and include things like red meat and steroids. Group 2b — which aspartame now falls into — are substances that are “possible carcinogens” and include pickled vegetables, engine exhaust fumes and aloe vera. Group 3 substances are “unclassifiable,” meaning there’s no credible evidence to date that they cause cancer. Group 3 includes coffee, for example.
The IACR’s decision on aspartame was based on three studies in humans that found a link between the consumption of artificially sweetened beverages and hepatocellular carcinoma, the most common type of liver cancer. There was also some evidence of an increased incidence of tumors in mice and rats who were given aspartame in their food, but the group noted that the studies had flaws. A summary of the evaluation was published Thursday in The Lancet, but the full report won’t be available for another six months, the WHO said.
Branca, who presented the conclusions of the Joint FAO/WHO Expert Committee on Food Additives, said that a panel of 13 experts across 15 countries didn’t find the evidence linking aspartame and cancer convincing.
“The panel felt that the studies that were getting positive results were limited in their design and in the quality of the interpretation of the data,” Branca said during the media briefing.
FDA scientists have previously reviewed the studies included by the IARC, and "identified significant shortcomings," the agency said.
The American Cancer Society said the science behind whether aspartame causes cancer is still evolving.
“We recommend people use today’s 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,” ACS chief scientific officer Dr. William Dahut said in a statement. One scientist from the organization participated in the IARC’s meeting last month to evaluate the health effects of aspartame.
It’s not clear how aspartame could potentially cause cancer.
Jotham Suez, a molecular microbiologist and immunologist at the Johns Hopkins Bloomberg School of Public Health in Baltimore, said that there are no definitive answers yet on possible mechanisms for how the sweetener is carcinogenic.
Suez, who was not involved with the WHO’s work, has published research that found artificial sweeteners can negatively affect the gut’s microbiome, which could potentially play a role in the risk for cancer, although more research is needed.
Despite the food additive committee’s conclusions that aspartame can be consumed safely at fairly high amounts, the WHO’s announcement may give some people pause, said Dr. James Farrell, a gastrointestinal oncologist at the Yale School of Medicine.
People may not know how to assess the risk for themselves, Farrell said.
Giving people clear information about their risk levels is important, given the popularity of aspartame and other artificial sweeteners.
But aspartame’s potential cancer risk as well as the guidance on daily intake “may not be relevant” to the majority of consumers, said George Kyriazis, an assistant professor of biological chemistry and pharmacology at the Ohio State University College of Medicine.
According to estimates from the WHO, people who are on the higher end of aspartame consumption generally get about 30 mg/kg a day — less than the acceptable daily limit of 40 mg/kg. The average person is getting 10 times less than the acceptable daily limit, the WHO said. 
“There’s a big difference between a person consuming 20 Diet Cokes a day or 15 Diet Cokes a day versus the average consumer that drinks a diet soda with a meal or has a couple of packages of Equal with coffee,” Kyriazis said of the possible risk.
Dr. Neil Iyengar, a medical oncologist at the Memorial Sloan Kettering Cancer Center, said that some people with a genetic risk for certain cancers want to do everything they can to lower their risk.
“This is information they would want,” he said.
Branca, of the WHO, said if people are unsure whether they’re consuming too much aspartame, there’s always an alternative.
“If consumers are faced with the decision of whether to take cola with sweeteners or one with sugar,” he said, “I think there should be a third option considered, which is to drink water instead.”
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