by Research into the gut microbiome has sparked a “revolution” in nutritional science, and in recent years dietary fiber has become the “new protein” – added in abundance to foods to nourish our gut and improve our health.
A recent study in mice, however, suggests that not all fiber supplements are equally beneficial.
A form commonly found in oats and barley, called beta-glucan, can control blood sugar and aid weight loss in mice fed a high-fat diet.
Researchers from the University of Arizona (UA) and the University of Vienna say it’s the only type of fiber supplement they’ve tested that reduced fat content and body weight in mice in 18 weeks.
Other fibers considered, including wheat dextrin, pectin, resistant starch, and cellulose, had no such effect, despite a significant change in the composition of the mouse microbiome compared to mice fed no fiber supplements.
“We know that fiber is important and beneficial; the problem is there are many different types of fiber,” says UA biomedical scientist Frank Duca.
“We wanted to know what type of fiber would be most beneficial for weight loss and improving glucose homeostasis so that we could inform the community, the consumer, and then also the agricultural industry.”
Dietary fiber is the primary source of energy for the bacteria living in our gut, yet less than 5% of people in the United States consume the recommended 25 to 30 grams (0.9 to 1 ounce) of fiber per day.
To compensate for this, fiber supplements and invisible fiber-rich foods are gaining popularity. But fibers are extremely diverse, so which ones should you choose?
Some fibers, such as oat beta-glucans and wheat dextrin, are water-soluble, meaning they are easily fermented by gut bacteria. Others, such as cellulose and resistant starch, are less soluble or insoluble, meaning they stick to other materials to form stool.
So far, write UA biomedical scientist Elizabeth Howard and colleagues, “there are no studies that have examined the role of various fibers in a cohort.”
To compensate for this, the current study tested several forms of fiber in a cohort of mice. Only beta-glucan was found to increase the number of Ileibacterium This bacteria was discovered in the intestines of mice. Other studies in mice have linked this bacteria to weight loss.
Indeed, well before the 10-week marker, mice fed beta-glucan showed reduced body weight and body fat content compared to mice fed other forms of fiber.
These results are consistent with those of another recent study by Duca, which fed barley flour, which is rich in beta-glucan, to rodents. Even though the rats continued to eat the same amount of their high-fat diet as before, their energy expenditure increased and they still lost weight.
Similar results were seen in mice fed beta-glucan in the new study. These animals also showed increased concentrations of butyrate in their gut, a metabolite produced when microbes break down fiber.
Butyrate induces the release of glucagon-like peptide-1 (GLP-1), the natural protein that synthetic drugs like Ozempic mimic to stimulate insulin release.
“Part of the benefits of dietary fiber consumption is the release of GLP-1 and other gut peptides that regulate appetite and body weight,” Duca says.
“However, we don’t think this is the only effect. We think butyrate may have other beneficial effects that are not related to gut peptides, such as improving the health of the intestinal barrier and targeting peripheral organs such as the liver.”
More research is needed before these findings can be extended to humans, but the results suggest that some fibers may be better suited for weight loss and insulin control than others.
The study was published in the Journal of nutrition.
