Aspartame listed as 'possible carcinogen,' regulators still consider it safe in moderation

A World Health Organization expert group that evaluates the safety of food additives for consumption by consumers has reaffirmed that the artificial sweetener aspartame is safe when consumed below certain daily levels.

The Joint Expert Committee on Food Additives (JECFA) said in a report released Thursday that people can safely consume 40 milligrams of aspartame per kilogram of body weight per day, the same level established in prior guidance from the committee. That would be the equivalent of about nine to 14 12-ounce cans of diet soda a day for an average adult.

"Our results do not indicate that occasional consumption should pose a risk to most consumers," said Francesco Branca, director of the Department of Nutrition and Food Safety at the WHO, during a press briefing. "We're not advising companies to withdraw products nor are we advising consumers to stop consuming altogether. We're just advising a bit of moderation."

Aspartame, which is an ingredient in brand-name artificial sweeteners including Equal and Sugar Twin, has been used in food and beverages since the 1980s. The U.S. Food and Drug Administration has also consistently found that aspartame is safe and doesn't put people's health at risk.

The industry group American Beverage says the report reinforces the safety of aspartame. "People all around the world can be confident in consuming food and beverages with aspartame," Kevin Keane, interim president and CEO of American Beverage, said in a statement.

A second WHO group, which assesses whether substances might have the potential to cause cancer, also released a new report on aspartame. This group, the International Agency for Research on Cancer (IARC), says that it is a "possible carcinogen," but notes that the evidence is limited and more research is needed.

However, the IARC determination is a hazard assessment based on limited evidence linking aspartame to liver cancer. It doesn't look at how likely it is to cause cancer or how large the risk is. This is also the first time the IARC has evaluated aspartame.

"This shouldn't really be taken as a direct statement that indicates that there is a known cancer hazard from consuming aspartame," said Mary Schubauer-Berigan, acting head of the IARC Monographs program, during a WHO press briefing. "In our view, this is really more a call to the research community to try to better clarify and understand the carcinogenic hazard that may or may not be posed by aspartame consumption."

Experts say people should instead focus on the JECFA recommendations regarding safe consumption levels when they're making decisions about their diet.

"I will concentrate on looking at what JECFA for recommends, what they will consider as a safe level, and go with that," says toxicologist and risk assessment expert Samuel Cohen, a professor at the University of Nebraska Medical Center. "It's always the quantity that makes the poison."

The FDA said in a statement that it disagrees with the IARC decision that research supports classifying aspartame as a possible carcinogen. "FDA scientists do not have safety concerns when aspartame is used under the approved conditions," an FDA official said in a statement.

Both the IARC and JECFA reports were published in summary form Thursday, and the full reports will be available in about six months.

The American Cancer Society welcomes the call for more research into aspartame, Dr. William Dahut, chief scientific officer at the American Cancer Society, told ABC News. "As data evolves, I do think people should be aware that recommendations could change," he said.

For now, people should use the new reports as an opportunity to evaluate their dietary choices overall, Dr. Dahut added, for sweeteners generally and also for other foods that have stronger links to cancer, like processed meats and alcohol.

Even with Thursday's guidance, people who are consuming close to the recommended safe levels of aspartame might want to cut back, the WHO's Francesco Branca said. "If you're approaching the limit, why take that risk?" he said.

Additionally, just because aspartame is considered safe doesn't mean it's the healthiest choice. In May, the WHO said that people should not replace sugar with artificial sweeteners if they're trying to lose weight or improve other areas of their health. Instead, they should cut back on sweetened foods in general.

"If consumers are faced with the decision of whether to drink cola with sweeteners, or one with sugar, I think there should be a third option considered," Branca said. "Which is to drink water instead."