Dietary fructose and glucose, which are prevalent in the Western diet, silence a key protein that is necessary for gut colonization, but not for utilization of these sugars, by a beneficial bacterium called Bacteroides thetaiotaomicron, according to new research from Yale School of Medicine.

The gut microbiota is critical to human health, and its composition can be modified by diet.

Until recently, scientists believed that sugar was absorbed into the intestine and never reached the gut.

However, recent studies have shown sugar can travel to the colon, where the microbiota resides.

“Given the high consumption of sucrose and fructose in the Western diet, we wanted to know what effect it was having on the composition of the gut microbiome,” said Yale Professor Eduardo Groisman, senior author of the study.

Professor Groisman and co-authors studied the effects of a high sucrose/glucose diet in mice on Bacteroides thetaiotaomicron, a species of bacterium associated with the ability to process healthy foods such as vegetables.

The researchers found that both fructose and glucose, which together form sucrose, block the production of a key protein called Roc, which is required for colonization of this beneficial bacterium in the gut.

When they engineered a strain of this bacterium that did not silence Roc in response to fructose and glucose, the strain had a colonization advantage in the guts of mice on a high sucrose/glucose diet.

“The role of diet in the gut microbiota goes farther than just providing nutrients,” Professor Groisman said.

“It appears that carbohydrates like sugar can act as signaling molecules as well.”

The study was published in the Proceedings of the National Academy of Sciences.

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Guy E. Townsend II et al. Dietary sugar silences a colonization factor in a mammalian gut symbiont. PNAS, published online December 17, 2018; doi: 10.1073/pnas.1813780115