However, they also added that the assessment was done based on 'limited evidence', and that aspartame remains safe for use in the previously recommended daily intake levels.
New Update: The WHO, on Friday, 14 July, released a joint statement by the International Agency for Research on Cancer (IARC), and the Food and Agriculture Organization (FAO) Joint Expert Committee on Food Additives (JECFA) classifying aspartame as a "possibly carcinogenic to humans".
After reviewing existing literature, the health bodies said they found limited evidence of cancer, specifically, hepatocellular carcinoma (a type of liver cancer) in humans.
Yes, but: The WHO's Joint Expert Committee on Food Additives (JECFA) concluded that "the data evaluated indicated no sufficient reason to change the previously established acceptable daily intake (ADI) of 0 - 40 mg/kg body weight for aspartame.".
Reality check: For clarity, one can of diet soft drink generally contains 200 or 300 mg of aspartame. So an adult that weighs around 70 kg would have to consume more than 9–14 cans per day to exceed the acceptable daily intake - assuming they aren't consuming other products with aspartame.
This is also why diet drinks with artificial sweeteners are not recommended for children.
Between the lines: You might not always be aware of how much aspartame you're really consuming. Artificial sweeteners like Aspartame are widely used in commonly used products, more than you would think.
Apart from diet soft drinks, they are also used in,
Ice cream (particularly, sugar-free ice cream)
Sugar-free chewing gum
Packaged Milk-based drinks
Cough drops, and chewable supplements
What they're saying: According to the folks at WHO, this review is an indication that more studies and investigations will be needed going forth to get a clearer picture.
“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," said Dr Francesco Branca, Director of the Department of Nutrition and Food Safety, WHO in the statement.