Artificial sweeteners may contribute to soaring levels of diabetes, according to a controversial study that suggests the additives could exacerbate the problem they are meant to tackle.
Researchers found that artificial sweeteners used in diet drinks and other foods can disrupt healthy microbes that live in the gut, leading to higher blood sugar levels - an early sign of diabetes.
Sweeteners such as saccharin, aspartame and sucralose are widespread in western diets and are often used to cut calories or prevent tooth decay. The additives are so common that scientists behind the latest study called for a reassessment of the “massive usage” of the chemicals.
“Our findings suggest that non-caloric artificial sweeteners may have directly contributed to enhancing the exact epidemic that they themselves were intended to fight,” the authors write in the journal Nature.
Eran Elinav, a senior author on the study at the Weizmann Institute of Science in Rehovot, said that while the evidence against the sweeteners was too weak to change health policies, he had decided to give them up.
But the study has left many experts unconvinced. The findings draw largely on tests of just one sweetener in mice, raising doubts about their relevance to people and other sweeteners. Large studies in humans have found that sugar substitutes can help people maintain a healthy weight and protect against diabetes.
“This new report must be viewed very cautiously,” said Stephen O’Rahilly, director of the Metabolic Diseases Unit at Cambridge University, “as it mostly reports findings in mice, accompanied by human studies so small as to be difficult to interpret.” Brian Ratcliffe, professor of nutrition at Robert Gordon University in Aberdeen, Scotland, said: “Most of the effects that they report relate to saccharin with little or no effect of aspartame. Their paper ought to be limited to ‘saccharin’ in the title rather than attributing the effects to all artificial sweeteners.” The UK is poised to fall in line with World Health Organisation (WHO) recommendations to halve sugar intake to 5% of daily calories, a move expected to drive sales of diet drinks and low-calorie foods.
In the first of a series of experiments, the scientists found that mice fed on three artificial sweeteners - saccharin, aspartame and sucralose - developed high blood sugar levels. But when the mice were given antibiotics to kill off their gut microbes, the ill effects disappeared.
The scientists then focused on saccharin. They transferred gut microbes from mice fed on the sweetener to different mice that had no gut bacteria of their own. Soon after, the recipient mice developed high blood sugar levels themselves. Genetic analyses of the gut microbes from mice fed on saccharin found that as a group they behaved differently, breaking down more carbohydrate in the diet than normal.
The scientists ran tests on 400 people and found that those who consumed the most artificial sweeteners had different gut microbes than others, and on average were heavier and more glucose intolerant.
In their final set of experiments, the scientists gave seven people the maximum allowed daily dose of saccharin for a week. Each dose was enough to sweeten around 40 cans of diet cola. At the end of the week, four in seven had high blood sugar levels and their gut microbes mirrored the changes seen in mice fed on the additives.
To round off the study, the researchers transferred bugs from the people who developed high blood sugar after massive doses of artificial sweeteners into mice that had no gut bugs of their own. These mice went on to develop high blood sugar too.
According to Elinav, the study shows that artificial sweeteners may contribute to higher blood sugar in mice and some people. One possible explanation is that artificial sweeteners let some microbes thrive at the expense of others, leaving a population that extracts more energy from the diet than normal.
