Dietary fiber is a food nutrient that is generally difficult to digest. It mainly comes from the cell walls of plants and includes cellulose, hemicellulose, resin, pectin, and lignin. Dietary fiber is indispensable for a healthy diet. Fiber plays an important role in maintaining a healthy digestive system. It is divided into soluble and insoluble dietary fibers. At the same time, getting enough fiber can also prevent cardiovascular disease, cancer, diabetes, and other diseases. Fiber can clean the digestive wall and enhance digestion. Fiber can also dilute and accelerate the removal of carcinogens and toxic substances from food, protect the fragile digestive tract and prevent colon cancer. Fiber can slow down digestion and excrete cholesterol most quickly, so blood sugar and cholesterol in the blood can be controlled at the optimal level.

Cellulose, hemicellulose, and lignin are three common types of water-insoluble fibers, which are found in plant cell walls; while pectin and gum are water-soluble fibers, which are found in non-fibrous substances in nature. Common foods such as barley, beans, carrots, citrus, flax, oats and oat bran are rich in water-soluble fiber. Water-soluble fiber can slow down the speed of digestion and excrete cholesterol most quickly, and help regulate immune system function, To promote the excretion of toxic heavy metals in the body. Therefore, the blood sugar and cholesterol can be controlled above the ideal level, and it can also help diabetic patients to improve insulin levels and triglycerides.

Dietary fiber can be divided into soluble dietary fiber and non-soluble dietary fiber.

Ⅰ. The main characteristics of dietary fiber:

1. Water absorption

Dietary fiber has a strong ability to absorb water or combine with water. This effect can increase the volume of feces in the intestine, speed up its transportation, and reduce the time for harmful substances to connect to the intestinal wall.

2. Viscosity

Some dietary fibers have strong viscosity and can form mucous solutions, including pectin, gum, and trehalose.

3. Combining the role of organic compounds

It has the effect of combining bile acid and cholesterol.

4. Cation exchange

It can combine inorganic salts, such as potassium, sodium, and iron ions in the gastrointestinal tract, to form a dietary fiber complex and affect its absorption.

5. Bacterial fermentation

Dietary fiber is easily digested by bacteria in the intestinal tract, and soluble dietary fiber can be completely digested by bacteria, while insoluble dietary fiber is not easy to be digested. The short-chain fatty acids produced after fermentation can be used as an energy source for intestinal cells and bacteria.

Ⅱ. The physiological functions of dietary fiber

1. Conducive to the digestion process of food

Dietary fiber can increase the time for food to chew in the mouth, promote the secretion of intestinal digestive enzymes, and accelerate the excretion of intestinal contents, all of which are conducive to the digestion and absorption of food.

2. Lower serum cholesterol and prevent coronary heart disease

Dietary fiber can be combined with cholic acid to lower blood lipids.

3. Prevent gallstone formation

Most gallstones are caused by over-saturation of cholesterol in the bile. When bile acids and cholesterol are out of balance, small cholesterol crystals will be precipitated to form gallstones. Soluble fiber for cholesterol can reduce the concentration of bile and cholesterol, reduce the saturation of cholesterol, and reduce the occurrence of cholelithiasis.

4. Promote colon function and prevent colon cancer

The proliferation of intestinal anaerobic bacteria can degrade neutral or acidic fecal sterols, especially bile acid, cholesterol and their metabolites, and the metabolites produced may cause cancer. Dietary fiber can inhibit anaerobic bacteria, promote the growth of aerobic bacteria, and reduce carcinogenic metabolites. At the same time, dietary fiber can also use its water absorption to expand the volume of feces, shorten the time of feces in the intestine, and prevent carcinogens and easy The long-term contact between the intestinal mucosa can reduce the possibility of cancer.

5. Prevent excess energy and obesity

Dietary fiber has a strong water absorption capacity, which can increase the volume of stomach contents and increase the feeling of fullness, thereby reducing the food and energy intake, which is beneficial to weight control and preventing obesity.

6. Maintain normal blood sugar balance and prevent diabetes

Soluble dietary fiber can reduce the increased sugar content of blood sugar after a meal, reduce insulin levels or improve the body's insulin sensitivity.

7. Prevent habitual total constipation, prevent esophageal hemorrhoids, etc.

Adults should consume 30 grams of dietary fiber daily.

Excessive intake is not beneficial to the body and can also affect the absorption and utilization of nutrients. This is because dietary fiber can be combined with calcium, iron, zinc, etc., thereby affecting the absorption and utilization of these elements.

Daily intake standard:

The daily intake of dietary fiber recommended by relevant international organizations is: The American Cancer Prevention Association recommends a standard of 30-40 grams per person per day, and the European Community Food Science Committee recommends a standard of 30 grams per person per day.

The World Food and Agriculture Organization recommends that the intake of normal people should be 27 grams per day. The Chinese Nutrition Society proposed in 2000 that the appropriate intake for adults is 30 grams per day. At present, the dietary fiber intake of Chinese people from daily food can only be Reach 8-12 g/day. In addition, 10-15 grams per day should be added to patients with "riches disease". For children and adolescents aged 2-20, the recommended intake is age plus 5-10 grams per day.

Ⅲ. The structure and characteristics of the main components of dietary fiber:

1. Cellulose

Cellulose cannot be digested by human intestinal enzymes. Cellulose is hydrophilic and acts to absorb water in the intestinal tract.

2. Hemicellulose

In the human large intestine, hemicellulose is easier to decompose by bacteria than cellulose. It has the effect of binding ions. Certain components in hemicellulose are soluble. Hemicellulose is mostly insoluble, and it also plays a certain physiological role.

3. Pectin 

Pectin is an amorphous substance that exists in the soft tissues of fruits and vegetables. It can be dissolved in hot solutions and forms a colloidal state when heated in acidic solutions. Pectin also has the ability to combine with interest.

4. Gum

The chemical structure of gum varies from source to source. The main ingredients are polysaccharides formed by uronic acid, half lactic acid, arabinose and mannose. It can be dispersed in water, has a giant viscosity, and can act as a thickening agent.

5. Lignin

Lignin is not a polysaccharide substance, but a polymer of phenyl propane, which has a complex three-dimensional structure. Because lignin is difficult to separate from cellulose in the cell wall, lignin is included in the composition of dietary fiber. Neither humans nor animals can digest it.

6. Resistant starch

Resistant starches include modified starches and starches that have been heated and then cooled. They are not absorbed in the small intestine.