Research into the gut microbiome has sparked a “revolution” in nutritional science, and in recent years dietary fiber has become the “new protein” that is added in large quantities to foods to nourish the gut and promote health.
However, a recent study in mice suggests that not all fiber supplements are equally beneficial.
A substance called beta-glucan, found in abundance in oats and barley, can control blood sugar levels and help mice lose weight on a high-fat diet.
Researchers from the University of Arizona (UA) and the University of Vienna say this was the only fiber supplement they tested that reduced fat content and body weight in mice within 18 weeks.
Other fibres tested, including wheat dextrin, pectin, resistant starch and cellulose, had no such effect, despite significantly altering the composition of the mice’s microbiota compared to mice that did not receive fibre supplements.
“We know that fiber is important and beneficial. The problem is, there are so many different types of fiber,” explains Frank Duca, a biomedical scientist at the University of Arizona.
“We wanted to know which types of fiber are most effective for weight loss and improving glucose homeostasis so we could inform local communities, consumers and the agricultural industry.”
Fiber is the main source of energy for the bacteria that live in the intestine, but fewer 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 foods with invisible fiber are becoming increasingly popular. But with so many different types of fiber, how do you choose?
Some fibres, such as oat beta-glucan and wheat dextrin, are soluble in water and can be readily fermented by gut bacteria, while others, such as cellulose and resistant starch, are poorly soluble or insoluble and therefore attach to other substances to form stool.
Elizabeth Howard, a biomedical scientist at the University of Arizona, and her colleagues write that to date, “no studies have examined the role of different fibers in a single cohort.”
To address this, the current study tested several types of fiber in one cohort of mice. They found that only beta-glucan increased the number of Infectious Bacteria found in the mice’s gut. Other studies in mice have shown that this bacteria is associated with weight loss.
As expected, well before the 10-week mark, the mice fed beta-glucan lost weight and body fat content compared to mice fed other forms of fiber.
The findings are consistent with another recent study by Dr Duca, who fed beta-glucan-rich barley flour to rodents, which increased their energy expenditure and lost weight, even though they continued to eat the same amount of high-fat food as before.
The new study found similar results in mice fed beta-glucan: These animals also had increased levels of butyrate, a metabolite produced when microbes break down fiber, in their gut.
Butyrate triggers the release of glucagon-like peptide-1 (GLP-1), a natural protein that synthetic drugs such as Ozempic mimic to stimulate insulin release.
“Part of the benefit of consuming fiber is due to the release of GLP-1 and other gut peptides that regulate appetite and weight,” Duca explains.
“But we don’t think that’s the whole story. We believe that butyrate may also have other beneficial effects that are unrelated to gut peptides, such as improving intestinal barrier health and targeting peripheral organs such as the liver.”
Although more research is needed before these results can be applied to humans, the findings suggest that some fibers may be better for weight loss and insulin control than others.
The study was published in the Journal of Nutrition.