Dietary fiber, or roughage, occurs in two separate forms: soluble and insoluble. Insoluble fiber cannot be digested by the body, but still plays a critical role in absorbing water from the digestive system and providing bulk to keep the intestinal muscles healthy and toned.
Soluble fiber, also known as prebiotic, viscous or fermentable fiber, cannot be digested either. Unlike insoluble fiber, however, soluble fiber is fermented by intestinal microbes into short-chain fatty acids and gases (including propionate and butyrate) which the body can digest.
Research has shown that diets high in fiber significantly reduce the risk of diabetes and obesity in humans and other animals. According to a research review published in the International Journal of Food Safety, Nutrition and Public Health in 2011, the widespread adoption of the Western diet has led to a reduction in fiber intake worldwide and a concurrent increase in health conditions such as obesity, diabetes and cardiovascular disease.
Physiologically, fiber has been shown to lower cholesterol levels, increase calcium availability, boost immune function, maintain gastrointestinal health and help regulate blood sugar levels.
Fiber causes glucose production, hunger suppression
Because soluble fiber is processed in the intestines, the French and Swedish researchers decided to investigate whether fiber's health-promoting properties might be related to the intestine's ability to produce glucose.
Like the liver and certain other organs, the intestine is capable of breaking down stored energy into glucose, in order to make energy available to the body between meals or at night. When the intestine produces glucose, the sugar is detected by the nerves in the walls of the portal vein, which collects blood flowing immediately out of the intestine. These nerves then signal the brain, which sends signals to the body designed to reduce the risk of obesity and diabetes: reduced hunger, increased rest-energy expenditure and reduced glucose production by the liver.
In order to examine the relationship between soluble fiber and intestinal glucose, the researchers fed rats and mice diets high in soluble fiber, propionate or butyrate. The researchers found that, in these rodents, genes and enzymes responsible for intestinal glucose synthesis became significantly more active. They also found that propionate was used directly by the intestine as part of the glucose production process.
In addition, rodents given a high-fiber, high-sugar and high-fat diet became less obese and developed less insulin resistance than rodents fed a high-sugar, high-fat low-fiber diet.
The researchers then performed the experiment again, this time with mice genetically modified to be unable to produce glucose in their intestines. In the genetically modified mice, a high-fiber diet offered no protection against obesity or diabetes; mice on the high-fiber diet became just as fat as mice on the low-fiber diet.
These findings not only help increase scientific understanding of the importance of dietary fiber but also highlight the important role played by healthy, naturally occurring intestinal flora. They also demonstrate the key role that the intestine plays in regulating the body's glucose levels.
Increasing your fiber intake is one of the easiest ways to combat the negative effects of a Western diet. In order to avoid unpleasant digestive side effects, fiber intake is best increased gradually and should be spread across all meals and snacks eaten during the course of the day.