Sugar substitutes may be linked to changes in gut microbiome - study

Sugar substitutes have had many unproven charges levelled against them — saccharine causes cancer, anyone? —  since they became popular in the late 19th century. A new study shows that non-nutritive sweeteners do in fact influence people’s microbiomes “in a way that can change their blood sugar levels”.

“The results were quite striking,” said immunologist professor Eran Elinav, of Israel’s Weizmann Institute of Science and the German National Cancer Centre. “The results seemed to suggest that gut microbes in the human body are rather responsive to each of the sweeteners [aspartame, saccharin, stevia and sucralose].”

University of Cape Town professor Joel Dave, head of endocrinology at Groote Schuur Hospital, said the gastrointestinal (gut) microbiome has been linked to the regulation of many important bodily processes that maintain a person’s health.

“There is now emerging data to show that alterations in the gut microbiome may be linked to the development of many diseases including obesity and diabetes,” he said, in response to the new research.

“The fact that non-nutritive sweeteners are being shown to affect the gut microbiome is concerning.  In the long term they could negatively affect body weight and blood glucose,” he said, calling for long-term studies on this.

Dietitian Jandri Barnard, spokesperson for the Association for Dietetics in SA, said: “Prolonged continuous exposure to artificial sweeteners could alter your sweet preferences, which could lead to enhanced intake of sugars throughout a person’s life.”

The intensely sweet taste of sweeteners could “interfere with the learning of basic sweet taste relations and the delivery of kilojoule intake”, and in turn negatively affect the regulation of metabolic processes in the body, she said.

The latest peer-reviewed research, published on Friday in the journal Cell, began in 2014 with mice. Once Elinav found that non-nutritive sweeteners changed the microbiomes of mice — with the potential to affect their insulin and glucose responses — he wanted to know if this was true for humans too.

For the human study, four groups of people were put on to non-nutritive sweeteners while two groups acted as controls, not on any sweeteners. The research team found that the sugar substitutes had similar effects on people’s guts to those on the mice.

“We found that two of the non-nutritive sweeteners, saccharin and sucralose, significantly affected glucose tolerance in healthy adults,” said Elinav. But the effects of sweeteners on individuals would differ because every person’s microbiome has a unique composition.”

The 120 participants were chosen out of more than 1,300 people who never used artificial sweeteners in their daily life. After they were exposed to the sweeteners, they had “very distinct changes in the composition and function of gut microbes”, said Elinav.

When the scientists transplanted microbial samples from individuals affected by the sweeteners into germ-free mice, without microbiomes of their own, the mice developed glycemic responses that “very significantly mirrored those of the donor individuals”.

Most scientific studies did not report a major effect of non-nutritive sweeteners on body weight and blood glucose, said Dave, but many of them were of short duration.

“There is conflicting data as to whether non-nutritive sweeteners can increase appetite and obesogenic hormones, thereby causing weight gain.”

He said studies suggested that non-nutritive sweeteners may raise the risk of developing metabolic syndrome — a cluster of conditions including high blood pressure that can increase the risk of diabetes, stroke and heart disease.

Sweeteners without calories are found in popular products such as diet sodas and sugar-free chewing gum, but these could be counterproductive for people pursuing weight loss and health, science suggests.

“We need to continue searching for solutions to our sweet tooth craving, while avoiding sugar, which is clearly most harmful to our metabolic health,” said Elinav. “In my personal view, drinking only water seems to be the best solution.” ​