Mice given a good helping of a particular type of dietary fiber become less obese and are protected from developing metabolic syndrome when fed a high-fat diet, according to studies by researchers at Georgia State University. A team led by Andrew Gewirtz, Ph.D., a professor in the Institute for Biomedical Sciences, found that adding the fermentable fiber inulin to a high-fat diet restored gut microbiota levels in mice, boosted gut epithelial cell production and induced expression of interleukin-22 (IL-22), which blocked gut microbiota from invading the epithelial cells and causing inflammation and metabolic syndrome.  

“This study revealed the specific mechanism used to restore gut health and suppress obesity and metabolic syndrome is the induction of IL-22 expression,” Prof. Gewirtz states. “These results contribute to the understanding of the mechanisms that underlie diet-induced obesity and offer insight into how fermentable fibers might promote better health.” The University of Georgia researchers, working with scientists at Pennsylvania State University and the University of Kentucky, report their findings in Cell Host & Microbes, in a paper entitled “Fiber-Mediated Nourishment of Gut Microbiota Protects against Diet-Induced Obesity by Restoring IL-22-Mediated Colonic Health.”

Eating a high-fat diet is linked with obesity and the development of metabolic syndrome, a group of conditions that can include high blood pressure and high blood sugar levels, excess fat around the waist, and abnormal cholesterol levels. In combination, these effects can increase the risk of diseases that include diabetes, heart disease, and stroke. Modern diets, which include highly processed, fiber-lacking foods, and high amounts of fat, are believed to affect the composition of gut microbiota and increase the risk of chronic inflammatory diseases, including metabolic syndrome.  A high-fat diet also destroys the normal level and complement of intestinal bacteria and reduces the production of epithelial cells lining the intestine, which allows gut bacteria to invade intestinal epithelial cells.

To investigate any benefits of adding dietary fiber to a high-fat diet, the University of Georgia team fed mice on either a standard chow, a high-fat diet with a very low level of insoluble cellulose fiber, or a high-fat diet supplemented with either fermentable inulin or cellulose, for four weeks.

They found that animals fed on the inulin-supplemented high-fat diet demonstrated reduced weight gain, were noticeably less obese, and had smaller fat cells than animals fed a low-fiber, high-fat diet. Inulin-enrichment was also linked with lower cholesterol levels, and the supplement prevented the animals from developing abnormal blood sugar levels. In contrast, enriching a high-fat diet with insoluble cellulose didn't result in the same level of beneficial effects on obesity or blood sugar.

Animals fed inulin-supplemented high-fat diets also exhibited restoration of gut microbiota, although not to the same levels as control animal fed a healthy chow. The addition of cellulose to high-fat diet had no effects on microbiota levels. “HFD [high-fat diet] decimates gut microbiota, resulting in loss of enterocyte proliferation, leading to microbiota encroachment, low-grade inflammation (LGI), and metabolic syndrome,” the authors write. “Enriching HFD with inulin restored microbiota loads, interleukin-22 (IL-22) production, enterocyte proliferation, and antimicrobial gene expression in a microbiota-dependent manner.…Thus, fermentable fiber protects against metabolic syndrome by nourishing microbiota to restore IL-22-mediated enterocyte function.”



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