Beta-glucan fibre from oats and barley helped mice lose weight, 2024 study

Gut microbiome research and the new focus on dietary fibre

Work on the microbes that inhabit our digestive tract has been described as a nutritional science “revolution”.

Over recent years, dietary fibre has been treated as the “new protein”, with manufacturers adding it generously to products in the hope of nourishing the gut microbiome and improving health.

Yet a 2024 mouse study indicates that fibre supplements are not all equally helpful.

Comparing fibre supplements in one mouse cohort

Researchers from the University of Arizona (UA) and the University of Vienna investigated multiple fibre types in a single cohort of mice, addressing what biomedical scientist Elizabeth Howard (UA) and colleagues say has been missing so far: “there is no study that has investigated the role of various fibers in one cohort.”

In the experiment, mice were given different fibre supplements while consuming a high-fat diet. The team tested beta-glucan (a fibre commonly found in oats and barley) alongside wheat dextrin, pectin, resistant starch, and cellulose.

According to the researchers, beta-glucan was the only supplement they examined that reduced a mouse’s fat mass and overall body weight within 18 weeks.

By contrast, the other fibres-wheat dextrin, pectin, resistant starch, and cellulose-did not produce the same change in body fat or weight, even though they altered the composition of the mouse microbiome markedly compared with mice that received 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 (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.”

Fibre types, solubility, and why supplements are popular

Dietary fibres provide a primary energy source for bacteria in the gut, but fewer than 5 percent of people in the United States meet the suggested daily intake of 25–30 grams of fibre.

As a result, fibre supplements and products fortified with “invisible fibre” have become increasingly popular. Given how varied fibres are, however, it remains unclear which options are most worth choosing.

Some fibres-including oat beta-glucans and wheat dextrin-are water-soluble, which means gut bacteria can ferment them readily.

Other fibres, such as cellulose and resistant starch, are less soluble or insoluble and tend to bind with other materials, helping to form stool.

Why beta-glucan from oats and barley stood out: Ileibacterium, butyrate, and GLP-1

Among the fibres examined, only beta-glucan increased levels of Ileibacterium in the mouse intestine. Previous mouse research has associated this bacterium with weight loss.

Consistent with that link, well before the 10-week point the beta-glucan-fed mice showed lower body weight and reduced body fat compared with mice given other fibre types.

The results also match findings from another recent study led by Duca, in which rodents were fed barley flour rich in beta-glucan. Despite continuing to eat the same amount of their high-fat diet, those rats increased their energy expenditure and lost weight regardless.

In the newer work, mice receiving beta-glucan similarly showed higher concentrations of butyrate in the gut-a metabolite produced when microbes break down fibre.

Butyrate prompts the release of glucagon-like peptide-1 (GLP-1), the naturally occurring protein that synthetic medicines such as Ozempic imitate 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.”

What the findings mean-and what they do not

Considerably more research is required before extending these findings to humans. Even so, the study suggests that certain fibres may be better suited than others for supporting weight loss and blood sugar control.

The study was published in the Journal of Nutrition.

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