The World Health Organization (WHO) has classified aspartame, an artificial sweetener commonly used in soft drinks, as "possibly" causing cancer, but it has not changed its recommanded limits on daily intake.
Aspartame is one of the world's most popular sweeteners, used in diet and sugar-free versions of foods.
Famous brands containing the sweetener include Diet Coke, Pepsi Max and Mars' Extra chewing gum.
Two panels of experts at the WHO have been reviewing whether there is any evidence that the substance is a potential hazard, and how much of a real-life risk that substance actually poses.
On Friday the International Agency for Research on Cancer (IARC), based in the southern French city of Lyon, said aspartame was a "possible carcinogen".
That classification, in fact, means there is not enough evidence to show a substance can cause cancer.
The category includes substances such as aloe vera and lead.
Another panel, the Geneva-based WHO and Food and Agriculture Organization Joint Expert Committee on Food Additives (JECFA), has the job of working out what the safe doses would be.
Having analysed the risk, JECFA said on Friday that it had found no convincing evidence of harm caused by aspartame and was keeping to the levels it had set in 1981.
This means the safe limits should remain at below 40mg per kilogram of body weight per 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.
"Our results do not indicate that occasional consumption could pose a risk to most consumers," said WHO's head of nutrition, Francesco Branca.
Obesity a greater risk
Some doctors have expressed concern that the new classification of "possible carcinogen" might sway drinkers of diet soda to switch to caloric sugar beverages.
Therese Bevers, medical director of the Cancer Prevention Center at the University of Texas said "the possibility of weight gain and obesity is a much bigger problem and bigger risk factor than aspartame could ever be".
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.
"Aspartame, like all low/no calorie sweeteners, when used as part of a balanced diet, provides consumers with choice to reduce sugar intake, a critical public health objective," said Frances Hunt-Wood, secretary general of the Brussels-based International Sweeteners Association.
In a press conference ahead of Friday's announcement, 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," he said.
(with newswires)
