Some artificial sweeteners can raise your blood sugar

Two artificial sweeteners, saccharin and sucralose, have been found to increase blood sugar levels despite being thought not to. This may be related to changes the sweeteners induce in gut microbes.

These sweeteners are a sugar alternative for people with metabolic conditions such as diabetes or for those looking to lose weight, as they are more than 200 times sweeter than sugar and contain few to zero calories.

Jotham Suez at Johns Hopkins University in Maryland and his colleagues tested the effects of four sugar substitutes on blood sugar in 120 adults in Israel without underlying health conditions. The participants reported that they did not consume low-calorie sweeteners during the six months prior to the study.

They were then divided into six groups and supplied with 1-gram packets of sweeteners. For two weeks, participants in four of these groups consumed two packets three times a day of either aspartame, sucralose, saccharin or stevia dissolved in water. The sweetener packets all contained at least 96 per cent glucose, as the sweeteners are so potent that only a small amount is needed –glucose is used as a bulking agent so the sweeteners can be packaged. The total daily dose of each sweetener was below the accepted daily intake determined by the US Food and Drug Administration. A fifth group consumed equivalent amounts of glucose powder over the same period and the last group had no supplement.

All participants wore continuous blood sugar monitors throughout the study and for a week before and afterwards. At nine points in the study, the participants completed a glucose tolerance test, which measures how effectively the body controls blood sugar levels after consuming glucose.

On average, the researchers found that people who consumed saccharin and sucralose had significant spikes in blood sugar after the glucose tolerance tests. Blood sugar remained stable or even decreased slightly in all of the other groups, even those consuming daily glucose – suggesting it is not the glucose in the sweetener packets that is raising blood sugar levels, says Suez.

While an increase in blood sugar is expected after eating glucose, people with an impaired blood sugar response have a greater increase in glucose levels and these levels stay elevated for longer, he says.

Suez and his team also analysed daily stool and saliva samples from the participants and found that all four sweeteners significantly altered the abundance, activity and types of bacteria in the gut and mouth. They also collected weekly blood samples and found corresponding changes in metabolites, or molecules that are by-products of digestion.

A few of the blood metabolite changes seen in the saccharin and sucralose groups are also seen in people with diabetes or vascular diseases. Some were in pathways known to play a role in the breakdown of sugars.

The researchers also transplanted stool samples from people eating saccharine, sucralose, glucose and no supplement into the digestive tracts of mice, and found that transplants from the saccharine and sucralose groups resulted in an increase in the mouse’s blood sugar after a meal.

This suggests it was the microbial changes that led to this outcome, says Suez. “The sweeteners themselves do not raise blood glucose,” he says, but seem to impair the body’s ability to manage glucose levels after eating through mechanisms mediated by the microbiome.

However, the health effects of these microbial and metabolic changes are still unknown. Suez hopes future trials will help untangle these relationships.

Alice Lichtenstein at Tufts University in  Massachusetts says longer studies are needed to determine whether the observed elevation in blood sugar is enough to cause health problems.

“We are definitely not saying switch to [sugar-sweetened beverages], which have been beyond a doubt associated with metabolic disease,” Suez says. “I would say if people can switch to water, that’s always the best option.”

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