A sweetener used in Diet Coke can cause cancer.
World Health Organisation (WHO) officials have declared that aspartame, a chemical that is also found in chewing gums and yoghurts, is "possibly carcinogenic to humans".
Dr. Mary Schubauer-Berigan, of the WHO's International Agency for Research on Cancer (IARC), explained that the sweetener could cause liver cancer even though there is only "limited evidence".
The organisation has now urged people to limit their consumption of sweetened products where possible.
Dr. Francesco Branca, of the WHO's Department of Nutrition and Food Safety, said: "If consumers are faced with a decision of whether to take cola with sweeteners or with sugar, I think there should be a third option considered, which is to drink water instead.
"There are alternatives that do not contain either free sugars or sweeteners and those should be the products that should be preferred by consumers."