The dietary fiber is composed of edible parts of plants that our small intestine is unable to digest or absorb and reach the large intestine intact. Among them are non-starch polysaccharides (cellulose, hemicellulose, gums and pectins). The term dietary fiber also includes a type of starch known as resistant starch (found in legumes, seeds and partially milled grains and some breakfast cereals) because it exceeds the digestion in the small intestine and reaches the large intestine intact. The dietary fiber is found in fruits, vegetables, legumes and whole cereal grains (wheat bran, oatmeal, whole grain bread or multi-grain, etc.)
Often, dietary fiber is classified according to their solubility in soluble or insoluble fiber. Both types of fiber are found in varying proportions in foods that contain fiber. Oats, barley, fruits, vegetables and legumes are good sources of soluble fiber. Whole grains and wholemeal bread are rich sources of insoluble fiber.
Dietary fiber intake is on the large intestine, where it is partially or completely fermented by intestinal bacteria. During the fermentation process, several byproducts are formed, short-chain fatty acids and gases. The health benefits of dietary fiber are derived from the combined effects of fermentation and by-products.
The main physiological effects attributed to dietary fiber affect bowel function, levels of blood glucose and blood cholesterol. Let's look at each one.
a) Bowel function
The dietary fiber, especially insoluble fiber helps prevent constipation to increase the weight of stool and reduce the duration of intestinal transit. This effect is even greater if the fiber consumption is associated with an increased intake of water. The short-chain fatty acids, fiber produced when fermented by the action of intestinal bacteria are a major source of energy for cells of the colon and can inhibit the growth and proliferation of cancer cells in the intestine. To improve bowel function, dietary fiber may reduce the risk of diseases and disorders, such as diverticular disease (pockets or sacs that form in the lining of the colon) or hemorrhoids, and can have a protective effect against colon cancer.
b) The levels of glucose in the blood
Soluble fiber can slow digestion and absorption of carbohydrates and hence reduce the rise in blood glucose that occurs after eating. This may help people with diabetes have better glycemic control.
c) Blood cholesterol
The results of several epidemiological studies reveal another role of dietary fiber in the prevention of coronary heart disease. Tests confirm the clinical results of these studies. The consistency of viscous fiber, such as pectin, rice bran or oat reduced serum total cholesterol and LDL cholesterol level (low-density lipoprotein or bad cholesterol). The investigations continue to demonstrate as well that a diet high in dietary fiber of mixed origin also protects against coronary heart disease.
d) Other effects
Although the prevention of constipation, improvement of blood glucose and lipid profiles in the blood are the main benefits derived from a diet rich in dietary fiber, there are other positive consequences.
For example, since the fiber increases the volume of the diet without adding calories, it can have an satiating effect and thus help control weight.
To enjoy the full effects of the fiber, vary the sources of fiber in the diet. Diets with fruits, vegetables, lentils, chickpeas or beans, whole grains and nuts not only provide dietary fiber, but also provide other nutrients and food components essential for optimal health.
Source: EUFIC (European Food Information)