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How a fiber-rich diet protects against obesity and diabetes

Jan 15th 2014 at 8:02 PM

Researchers have long known that a diet rich in fiber can help protect against diabetes and obesity, but they have been unclear as to how. Now, investigators from France and Sweden say they have unveiled this mechanism. This is according to a study recently published in the journal Cell.

The research team, led by Giles Mithieux of the French National Centre for Scientific research (Centre National de la Recherche Scientifique - CNRS), explains that many foods high in fermentable fiber, such as cabbage, beans and most sweet fruit and vegetables, are unable to be digested by the intestine directly.

Instead, intestinal bacteria ferments these fibers into short-chain fatty acids, including butyrate and propionate. These fatty acids can then be absorbed by the body.

The investigators say that it is a well-known fact that a high-fiber diet has a protective effect against diabetes and obesity, but what are the mechanisms behind this?

To find out, the researchers looked to the glucose-producing capabilities of the intestine.
Intestine 'triggers protective effects' from fiber

The intestine synthesizes glucose and releases it into the bloodstream at night and between meals.
Enzyme
This picture highlights the enzyme responsible for the final reaction in glucose production of the intestine in red.
Image credit: Inserm/MITHIEUX G. & BESNARD P

The researchers explain that glucose has certain elements that are detected by nerves located in the vein that collects blood from the intestine - known as the portal wall. A nerve signal is then transmitted to the brain.

The brain then activates a series of defenses against diabetes and obesity in response to the signal. The defenses include increased satiety, increased energy expenditure during periods of rest and less glucose production from the liver.

The investigators analyzed rats and mice who were fed diets supplemented with fermentable fibers, propionate or butyrate, alongside rodents fed a control diet, in order to establish a connection between glucose production by the intestine and fermentable fibers.

All animals demonstrated a high expression of genes and enzymes that are responsible for the glucose synthesis in the intestine. Furthermore, they found that the animals' intestines increased the production of glucose by using propionate as a precursor.
Fiber-enriched diet staved off diabetes and weight gain in mice

The study revealed that mice who had a diet enriched with fibers - but that was high in both fat and sugar - gained significantly less weight, compared with mice who were fed a diet without fiber supplementation.

Additionally, because of the increased sensitivity to insulin, mice who ate a high fiber diet were also protected against diabetes.

Using mice whose intestines had been genetically engineered to stop producing glucose, the investigators repeated the experiment. From this, the researchers found that the mice gained weight and developed diabetes.

These findings suggest that it is the glucose-producing activity of the intestines as a result of propionate and butyrate, and intestinal bacteria, that cause fermentable fibers to protect against obesity and diabetes.

The investigators conclude that their research may lead to the development of new treatments or preventions for diabetes and obesity.

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