Beta-Glucan May Aid Weight Loss and Blood Sugar Control in Mice

Fibre and the gut microbiome

Research into the gut microbiome has sparked a ‘revolution’ in nutrition science. Over the past few years, dietary fibre has been treated as the “new protein”, with generous amounts added to foods to nourish the gut and support health.

Yet a recent mouse study indicates that fibre supplements do not all offer the same benefits.

Beta-glucan, a type of fibre commonly present in oats and barley, may help regulate blood sugar and support weight loss in mice eating a high-fat diet.

Scientists from the University of Arizona (UA) and the University of Vienna report that, among the fibre supplements they assessed, beta-glucan alone reduced both body weight and fat content in mice over 18 weeks.

The remaining fibres tested - wheat dextrin, pectin, resistant starch and cellulose - did not produce this result. This was despite substantial changes to the composition of the mouse microbiome compared with mice receiving no fibre supplements.

“We know that fiber is important and beneficial; the problem is that there are so many different types of fiber,” explained biomedical scientist Frank Duca from UA in July.

“We wanted to know what kind of fiber would be most beneficial for weight loss and improvements in glucose homeostasis so that we can inform the community, the consumer, and then also inform the agricultural industry.”

Why different dietary fibres matter

Dietary fibre provides the primary energy source for bacteria living in the gut. Nevertheless, fewer than 5 per cent of people in the United States consume the recommended 25–30 grams of fibre each day.

As a result, fibre supplements and foods fortified with ‘invisible fibre’ have become increasingly popular. However, given the vast diversity of fibres, it is not clear which option people should choose.

Certain fibres, including oat beta-glucans and wheat dextrin, dissolve in water and are therefore readily fermented by gut bacteria. Others, such as cellulose and resistant starch, are less soluble or insoluble, so they bind to other matter to form stool.

Until now, biomedical scientist Elizabeth Howard of UA and colleagues write, “there is no study that has investigated the role of various fibers in one cohort.”

To address this gap, the new research examined several fibre types within a single group of mice. Beta-glucan was the only one found to raise levels of Ileibacterium in the mouse gut. Previous mouse research has associated this bacterium with weight loss.

Beta-glucan, body weight and blood sugar

Well before the 10-week point, mice given beta-glucan had lower body weight and body-fat levels than those receiving the other fibre types.

The results are consistent with another recent study by Duca, in which rodents were given barley flour containing high levels of beta-glucan. Although the rats kept consuming the same quantity of their high-fat diet, they expended more energy and lost weight regardless.

Mice fed beta-glucan in the latest study showed a comparable response. They also had higher gut concentrations of butyrate, a metabolite produced when microbes break down fibre.

Butyrate prompts the release of glucagon-like peptide-1 (GLP-1), the natural protein imitated by synthetic medicines such as Ozempic 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 think that there are other beneficial things that butyrate could be doing that are not gut peptide related, such as improving gut barrier health and targeting peripheral organs like the liver.”

Considerably more research will be necessary before these findings can be applied to people. Still, the results indicate that certain fibres could be more suitable than others for weight loss and insulin regulation.

The study was published in the Journal of Nutrition.

An earlier version of this article was published in July 2024.