The sweetener aspartame is a "possible carcinogen" but it remains safe to consume at already-agreed levels, the World Health Organization (WHO) declared on Friday, July 14.
Aspartame is one of the world's most popular sweeteners, used in products from Coca-Cola diet sodas to Mars' Extra chewing gum.
In a press conference ahead of the announcement on Friday, the WHO's head of nutrition, Francesco Branca, suggested consumers weighing beverage choices consider neither aspartame nor sweetener.
"If consumers are faced with the decision of whether to take cola with sweeteners or one with sugar, I think there should be a third option considered - which is to drink water instead," Branca said.
In its first declaration on the sweetener, announced early on Friday, the International Agency for Research on Cancer (IARC), based in Lyon, France, said aspartame was a "possible carcinogen".
A carcinogen refers to something that can cause cancer.
The announcement does not take into account how much a person would need to consume to be at risk, which is considered by a separate panel, the WHO and Food and Agriculture Organization (FAO) Joint Committee on Food Additives (JECFA), based in Geneva.
After undertaking its own comprehensive review, JECFA said on Friday that it did not have convincing evidence of harm caused by aspartame, and continued to recommend that people keep their consumption levels of aspartame below 40mg/kg a day.
The WHO said the existing consumption levels meant, for example, that a person weighing 60-70kg would have to drink more than 9-14 cans of soda daily to breach the limit, based on the average aspartame content in the beverages - around 10 times what most people consume.
"Our results do not indicate that occasional consumption could pose a risk to most consumers," said Branca.
Several scientists not associated with the reviews said the evidence linking aspartame to cancer is weak. Food and beverage industry associations said the decisions showed aspartame was safe and a good option for people wanting to reduce sugar in their diets.
The IARC panel said on Friday it had made its ruling based on three studies in humans in the United States and Europe that indicated a link between hepatocellular carcinoma, a form of liver cancer, and sweetener consumption, the first of which was published in 2016.
Some doctors expressed concern that the new classification of "possible carcinogen" might make drinkers of diet soda to switch to caloric sugar beverages.
Therese Bevers, medical director of the Cancer Prevention Center at the University of Texas MD Anderson Cancer Center, in Houston, said "the possibility of weight gain and obesity is a much bigger problem and bigger risk factor than aspartame could ever be."