NEW YORK, Feb 3: Research on the gut microbiome has sparked a "revolution" in nutritional science, with dietary fiber gaining significant attention in recent years. Once considered a secondary nutrient, fiber has now become the "new protein," frequently added to foods to support gut health and overall well-being.

However, a recent study on mice suggests that not all fiber supplements offer the same benefits. Beta-glucan, a type of fiber found in oats and barley, has been shown to help control blood sugar levels and aid in weight loss in mice on a high-fat diet. Researchers from the University of Arizona (UA) and the University of Vienna found that beta-glucan was the only fiber supplement tested that reduced both fat content and body weight in mice over 18 weeks.

Other fibers, such as wheat dextrin, pectin, resistant starch, and cellulose, did not have the same effect, despite significantly altering the composition of the mouse microbiome when compared to mice not given fiber supplements.

"We know fiber is important and beneficial; the challenge is that there are so many different types of fiber," explained biomedical scientist Frank Duca from UA in July. "We wanted to determine which types of fiber are most beneficial for weight loss and improving glucose control, to inform the community, consumers, and the agricultural industry."

Dietary fibers are the primary energy source for the bacteria that live in our gut. Yet, less than 5% of people in the U.S. meet the recommended intake of 25–30 grams of fiber per day. To fill the gap, fiber supplements and "invisible fiber"-infused foods have become more popular. But given the diversity of fibers, which one should we choose?

Some fibers, like oat beta-glucans and wheat dextrin, are water-soluble and easily fermented by gut bacteria. Others, such as cellulose and resistant starch, are less soluble or insoluble, helping form stool. Until now, no study had examined the role of various fibers in the same group of subjects.

In this study, the researchers tested several types of fiber on a single group of mice. Only beta-glucan was found to increase the number of Ileibacterium bacteria in the mouse intestine. Other studies have linked this bacterium to weight loss. By the 10-week mark, mice fed beta-glucan showed a noticeable reduction in body weight and fat compared to those fed other fiber types.

These findings align with a previous study by Duca, which involved feeding barley flour, rich in beta-glucan, to rats. Despite maintaining their high-fat diet, the rats increased their energy expenditure and lost weight. A similar effect was observed in the mice in the current study. These mice also showed higher concentrations of butyrate in their guts, a metabolite produced when microbes break down fiber.

Butyrate is known to stimulate the release of glucagon-like peptide-1 (GLP-1), a natural protein that synthetic drugs like Ozempic mimic to encourage insulin release. "Part of the benefits of consuming dietary fiber is through the release of GLP-1 and other gut peptides that regulate appetite and body weight," said Duca. "However, we don't think that's all of the effect. We believe that butyrate might also be improving gut barrier health and targeting other organs like the liver."

Although more research is needed before these findings can be applied to humans, the results suggest that certain fibers may be more effective for weight loss and controlling insulin than others.

The study was published in the Journal of Nutrition.