June 18, 2021
Keio University Faculty of Pharmacy
A research group at Keio University has revealed that gut bacteria suppress diarrhea caused by the consumption of artificial sweeteners. This research is the result of a study by a group led by Professor Yungi Kim, including Koya Hattori (then a student in the master's program at the Graduate School of Pharmaceutical Sciences, Keio University) and Masahiro Akiyama, Project Lecturer at the same Faculty of Pharmacy.
Sugar alcohols such as sorbitol and mannitol are widely used as low-calorie artificial sweeteners in products like candies, gums, and beverages. However, excessive consumption of sugar alcohols is known to cause loose stools and, in some individuals, severe diarrhea accompanied by weight loss. While there are individual differences in susceptibility to sugar alcohol-induced loose stools and diarrhea, the underlying cause has remained unknown.
In this study, by using germ-free mice (which have no gut bacteria) and mice whose gut microbiota were disrupted with antibiotics, we found that gut bacteria are a key factor in preventing sugar alcohol-induced diarrhea. We also found that mice that did not develop sugar alcohol-induced diarrhea had a higher abundance of bacterial groups from the order Enterobacteriales or Clostridiales in their gut, and that administration of sugar alcohols increased the population of the Enterobacteriales group in the gut. Therefore, we searched for gut bacteria within the Enterobacteriales group that could suppress sugar alcohol-induced diarrhea and discovered that Escherichia coli (E. coli), which can utilize sugar alcohols as a nutrient source, has the effect of suppressing this condition. In fact, E. coli that were genetically modified to be unable to utilize sugar alcohols as a nutrient source could not suppress sugar alcohol-induced diarrhea.
These findings make it clear that the onset of sugar alcohol-induced diarrhea can be prevented by gut bacteria such as E. coli that have the ability to consume sugar alcohols.
Currently, processed foods containing artificial sweeteners are prevalent in the market. Since many artificial sweeteners are not easily digested and absorbed in the gastrointestinal tract, they tend to reach the large intestine, and it has been pointed out that they may consequently have a negative impact on the gut environment. This study newly revealed that commensal E. coli in the gut play a protective role against the adverse effects on the intestine induced by artificial sweeteners. Although E. coli often has an image of being a so-called "bad bacterium" because some strains can cause infectious diseases or are associated with inflammatory diseases, many E. coli are non-pathogenic. It is also known that they play a role in aiding food digestion and protecting the host from harmful microorganisms, and some E. coli strains are even used as probiotics. In the future, the practical application of new probiotics, such as E. coli that can suppress the adverse effects (like diarrhea) of artificial sweeteners, is expected.
The results of this research were published in the online edition of the international academic journal "Nutrients" on June 12, 2021.
For the full press release, please see below.