What is dietary fiber?
Fiber is a large group of nutrient compounds. Dietary fiber is not usually digested or absorbed in the stomach or small intestine. It is present in almost all plant based foods. Whole foods contain more fiber than processed foods.
Dietary fiber includes oligosacharides, non-starch polysaccharides, lignin and similar polysaccharides. Solubles fiber consists of pectins, gums and polysaccharides. Insolubles fiber is cellulose, hemicellulose and lignin. Soluble and insoluble fiber act in different ways in the body. Both have positive health effects.
What can fiber do?
Fiber can prevent diabetes or lessen the negative health effects of already existing diabetes. Dietary fiber has the same positive impact on cardiovascular disease and colon cancer.
More fiber can reduce the risk of high blood lipid levels, high cholesterol levels and high blood sugar. Fiber helps to prevent infections. It reduces systemic inflammation. Pregnant women eating more fiber have reduced risk of preeclampsia. And dietary fiber can improve memory and mood.
High fiber diets make softer and bulkier stools which normalize bowel movements. This also reduces risk of hemorrhoids and diverticular disease. Body weight tends to normalize because fiber is filling and stays in the digestive tract longer than low fiber foods.
How does dietary fiber work?
In the upper digestive tract, fiber makes everything more viscous. It also bonds with many nutrients. Both of these actions slow absorption into the bloodstream. This is how fiber reduces and moderates amounts of glucose in the blood. Insulin response is then also reduced, eliminating the huge swings that can eventually lead to diabetes.
Fiber acts as food for beneficial bacteria in the digestive tract. Those bacteria then have a direct impact on our immune system and on activating/deactivating certain genes that regulate hunger, cholesterol production, inflammation response and other bodily functions. It seems to be through our bacteria that more fiber lowers cholesterol and prevents cardiovascular disease.
By speeding the stool through the colon and making it easier to pass, fiber reduces contact time between any toxins and/or carcinogens in the waste with the intestinal wall. This is the probable mechanism for reducing colon cancer rates. Softer stool(because of the extra water held by fiber) causes less damage to the lining of the colon and anus and reduces straining during elimination, a major cause of hemorrhoids.
The extra bulk provided by a high fiber diet, combined with the extra time spent in the stomach and small intestine, increase and extend feelings of fullness. Lower and more constant blood glucose levels(and associated insulin spikes) reduce hunger cravings. Along with hunger regulating genes that work correctly, more fiber makes maintaining a healthy body weight much easier.
How to get more fiber
The best way to get more fiber is to eat a healthy whole food diet. Whole foods such as vegetables, fruits, nuts, beans and whole grains, are full of fiber. These foods naturally contain a wide variety of fiber types, both soluble and insoluble, which is better for health than the single kind of fiber provided by most fiber supplements. Whole foods also provide high levels of usable nutrients along with all that fiber.
Processed foods like white wheat flour, pearled barley and white rice have been stripped of almost all fiber and other nutrients. Most canned and frozen fruits and vegetables are also lower in fiber than the fresh versions. Peeling makes them prettier and more tender but removes much of the fiber and nutrition.
Following are links to more in-depth articles about dietary fiber and its connection to our health.