1. What is dietary fiber?

It can be simply understood as: dietary fiber is a kind of polysaccharide (also a kind of carbohydrate), which cannot be digested and absorbed by gastrointestinal tract, nor can it produce energy. It is juxtaposed with the traditional six kinds of nutrients: protein, fat, carbohydrate, vitamins, minerals and water. It has been supplemented and identified as the seventh category of nutrients by the nutritional science community. (Also known as resistant dextrin)

2. Classification: soluble and non-soluble dietary fiber

(1)  Soluble dietary fiber: it can be dissolved in water, swell when absorbing water, and can be hydrolyzed by microorganisms in large intestine. Soluble dietary fiber mainly includes pectin, vegetable gum and so on.

It is mostly found in vegetables, fruits, whole grains, beans, konjac, and other foods.

(2)  Insoluble dietary fiber: Insoluble dietary fiber, cellulose, hemicellulose and lignin. t mainly exists in the plant surface cortex and unprocessed gluten, whole wheat, grains, beans, rhizomes, peels and so on.

3. Functions of dietary fiber

(1) Improve intestinal function: non soluble dietary fiber will absorb too much intestinal colonies and fallen waste in the intestines and stomach, and then absorb water to expand, so as to increase stool volume, promote gastrointestinal peristalsis and accelerate defecation. At the same time, a small amount of cholesterol, fat and heavy metals in food will be excreted with stool.

(2) Prevention of colon cancer: faster excretion of stool also means that it stays in the intestinal tract for a shorter time, which can prevent carcinogens and easily infected intestinal mucosa growth time contact, thereby reducing the possibility of cancerization.

(Note: the above two items are adjusted according to one's own constitution: increasing dietary fiber intake does not necessarily contribute to total constipation, but if it is due to insufficient fiber, it should play a role.)

(3) Weight control: It cannot be absorbed by the stomach and intestines, and it has more satiety than ordinary grains.

(4) Stabilize blood sugar: It can delay the absorption and digestion of glucose, the rapid rise of blood sugar after a meal, as well as reduce blood sugar fluctuations.

(5) Lower cholesterol: soluble dietary fiber can reduce the stimulation of cholesterol synthesis in the liver, thereby reducing the synthesis of cholesterol, and the substances decomposed in the intestine can also inhibit the synthesis of cholesterol.

(Note: The above two are due to the effect of butyrate. Through the fermentation of dietary fiber, the intestinal flora will produce three main short-chain fatty acids in the intestinal lumen, namely acetate, propionate and butyrate.)

4. Foods which are rich in dietary fiber

(1) Fruit: avocado, guava and many other dietary fiber are hidden in the fruit skin, after peeling, the loss of dietary fiber can reach 24% - 46%

(2) Vegetables: lotus root, carrot, broccoli, celery, pumpkin, cauliflower, spinach, cauliflower, cabbage, eggplant and so on.

(3) Beans: soybeans, black beans, red beans, mung beans, and other beans.

(4) Coarse grains: potatoes, tubers, oats and so on.

(5) Bacteria and algae: tremella, agaric, Tricholoma, laver and so on.

(6) Nuts: almond, walnut, chestnut, almond, etc.

Note: the gluten in vegetables is not dietary fiber. If there are these tendons, it does not mean that the amount of fiber is high.

For example: Celery (the tendons in vegetables are the vascular bundles of plants. They are mostly found in stems and leaves. They mainly transport water, inorganic salts and organic nutrients to plants. In addition, they also support the plant body. These two are different substance.)

5. Intake recommendations

(1)  The World Health Organization recommends: supplement 25 grams of dietary fiber every day.

(2)  The US Department of Health recommends that adult men supplement 38 grams of dietary fiber daily, and adult women supplement 25 grams of dietary fiber daily.

(3)  China's 2013 version of the "Reference Intake of Dietary Nutrients for Chinese Residents" recommends that the recommended dietary fiber intake for adults is 25 to 30 grams. However, using any standard calculation, the average daily dietary fiber intake of 11 grams of Chinese people is far from the recommended value.

In fact, having said so much, we just want to express: There is no standard for how much dietary fiber you eat. Different countries and different institutions have different amounts. With the same fiber intake, some people feel very good after eating it, while others have frequent flatulence, excessive farts, diarrhea, and constipation after eating. The reason is that the so-called "standard" is not necessarily suitable for everyone.

6. Dietary fiber is not as much as possible

Dietary fiber is not absorbed by the human body. If you take too much dietary fiber, it is easy to cause iron, zinc, magnesium, calcium and other minerals difficult to be absorbed by the body, and may cause some people to have flatulence and abdominal distension.

In addition, some dietary fiber will absorb water, so you should add more water after eating. If you drink less water, it may cause constipation.

7. How to intake dietary fiber

(1) It is recommended to distribute the amount of dietary fiber evenly among the three meals a day.

(2) It is suggested that vegetables should be more than fruits every day. Most vegetables have higher fiber content than fruits, and fruits have fructose, so excessive intake may cause obesity.

(3) People with poor gastrointestinal function are not suitable for intake of most dietary fiber, such as the elderly, and those who have undergone gastrointestinal surgery, chemotherapy and other diseases.

8. Selection of dietary fiber products

You must first look at the ingredient list. Some businesses will add saccharin and other additives for the taste, so pay attention to the purchase, and it is best to choose products with less additives.

(1) Insoluble dietary fiber (take whole grain digestive biscuits as an example): The top raw materials are wheat flour, wheat bran, oats and so on. However, the calories and fat become very high because of the pursuit of taste. For the same amount of dietary fiber, you only need to eat 200 grams of vegetables to make up.

(2) At present, the health care type of dietary fiber on the market (soluble dietary fiber): it is extracted from Konjac (especially Amorphophallus konjac), corn (also known as resistant dextrin) and lettuce (also known as inulin), belonging to fructooligosaccharides and oligosaccharides.

It can be taken with warm water or added to hot soup, porridge, fruit juice and other foods. And they are all taken before or with meals.

Note: the effect of soluble dietary fiber on stabilizing blood glucose and lowering cholesterol should be considered together with the contents related to sugar, so as to make us more clear about its mechanism of action.