The World Health Organization's cancer agency has deemed the sweetener aspartame — found in diet soda and countless other foods — as a "possible" cause of cancer, while a separate expert group looking at the same evidence said it still considers the sugar substitute safe in limited quantities.
The differing results of the coordinated reviews were released early Friday. One came from the International Agency for Research on Cancer, a special branch of the WHO. The other report was from an expert panel selected by WHO and another U.N. group, the Food and Agriculture Organization.
The Lyon, France-based cancer agency periodically reviews potential cancer hazards, but doesn't determine how likely they are to cause cancer in their evaluations which range from "possibly" carcinogenic to "probably" to cancer-causing.
Aspartame joins a category with more than 300 other possible cancer-causing agents, including things like aloe vera extract, Asian-style pickled vegetables and carpentry work.
The guidance on use of the sweetener, though, isn't changing.
"We're not advising consumers to stop consuming (aspartame) altogether," said WHO's nutrition director Dr. Francesco Branca. "We're just advising a bit of moderation."
Here's a look at the announcement:
What is aspartame?
Aspartame is a low-calorie artificial sweetener that is about 200 times sweeter than sugar. It is a white, odorless powder and the world's most widely used artificial sweetener.
Aspartame is authorized as a food additive in Europe and the U.S. and is used in numerous foods, drinks such as Diet Coke, desserts, chewing gum, medications including cough drops and foods intended to help with weight loss. It's in tabletop sweeteners sold as Equal, Sugar Twin and NutraSweet.
Aspartame was approved in 1974 by the U.S. Food and Drug Administration with an acceptable daily intake of 50 milligrams per kilogram of body weight. According to the FDA, a person weighing 132 pounds (60 kilograms) would need to consume about 75 aspartame packets to reach that level.
U.N. experts evaluated the safety of aspartame in 1981 and set the safe daily limit slightly lower, at 40 milligrams of aspartame per kilogram.
David Spiegelhalter, an emeritus statistics professor at Cambridge University, said the guidance means that "average people are safe to drink up to 14 cans of diet drink a day … and even this 'acceptable daily limit' has a large built-in safety factor."
What did the two groups say?
WHO's cancer agency, IARC, convened its expert group in June to assess the potential of aspartame to cause cancer. It based its conclusion that aspartame is "possibly carcinogenic" on studies in humans and animals that found "limited" evidence that the compound may be linked to liver cancer.
In a separate evaluation, experts assembled by WHO and the food agency updated their risk assessment, including reviewing the acceptable daily intake. They concluded there was "no convincing evidence" at the currently consumed levels that aspartame is dangerous; their guidelines regarding acceptable levels of consumption were unchanged.
The move comes weeks after the WHO said that non-sugar sweeteners don't help with weight loss and could lead to increased risk of diabetes, heart disease and early death in adults.
Should I be concerned about getting too much?
Not as long as you don't exceed the guidelines. The FDA said scientific evidence continues to support the agency's conclusion that aspartame is "safe for the general population," when used within limits.
Almost any substance can be dangerous in excessive amounts, said David Klurfeld, a nutrition expert at the Indiana University School of Public Health-Bloomington.
"The dose makes the poison," said Klurfeld, who previously served on an IARC panel. "Even essential nutrients like vitamin A, iron and water will kill you within hours if too much is consumed."
So what should consumers do?
WHO's Branca said it was acceptable for people to consume a "pretty large" amount of aspartame without suffering any ill effects. "High consumers" might want to cut back, he said.
Dr. Peter Lurie, executive director of the Center for Science in the Public Interest, which previously nominated aspartame for IARC review, said there's an easy choice for consumers.
"At least when it comes to beverages, our message is your best choice is to drink water or an unsweetened beverage," he said.
Most people, though, probably don't pay much attention to IARC evaluations. The agency has previously classified processed meat like hot dogs and bacon as cancer-causing, noting in particular its link to colon cancer. That move surprised even others in the scientific community — the U.K.'s biggest cancer charity reassured Britons that eating a bacon sandwich every so often wouldn't do them much harm.
What does this mean for the food and beverage industry?
Food and beverage producers say there's no reason to avoid products with aspartame.
"There is a broad consensus in the scientific and regulatory community that aspartame is safe," the American Beverage Association said in a statement.
WHO's Branca said the agency advises food manufacturers in general to "use ingredients that do not require the addition of too much sugar." After the latest assessments of aspartame, Branca said that using sweeteners "is probably not the way forward."