Dietary fiber is a polysaccharide that is neither digestible nor absorbable by the body, nor can it produce energy. Dietary fiber is divided into two main categories: soluble dietary fiber and insoluble dietary fiber. Soluble dietary fiber mainly refers to pectin, gum and so on. Insoluble dietary fiber mainly comes from cereals, whole wheat flour and brown rice, oats, beans, vegetables and fruits, etc. The best source is whole grain. One of the main components of soluble dietary fiber is glucan, a soluble dietary fiber with high water absorption. Soluble dietary fiber can intertwine with carbohydrates in the gastrointestinal tract, thus delaying the absorption of carbohydrates. And insoluble fiber can promote gastrointestinal peristalsis, so that food passes through the gastrointestinal tract quickly, reducing absorption, and absorbing water in the colon to soften stools, which is very helpful for constipation patients.