Dietary fiber is a kind of polysaccharide, which can neither be digested and absorbed by gastrointestinal tract nor produce energy. Therefore, it was once considered as a "non-nutritive substance" and has not been paid enough attention for a long time.
However, with the in-depth development of nutrition and related sciences, people gradually found that dietary fiber has very important physiological functions. So, today, dietary fiber has become a concern of academic circles and ordinary people, and it is recognized as the seventh kind of nutrient by the nutrition academic circles, which ranks with the traditional six nutrients-protein, fat, carbohydrates, vitamins, minerals and water.
About 10,000 years ago, after the establishment of the earliest agricultural society, people began to choose high-fat animal foods, while still eating a lot of high-fiber plant foods to satisfy their hunger. It was not until the invention of rough grain processing technology that Egyptians first ate "white bread". Later, the health-conscious ancient Greeks found that when they ate whole wheat brown bread, their stools increased. After a long period of time, people's interest in food repeatedly wandered between "coarse grains" and "flour rice".
Our people's diet is mainly cereal, supplemented by vegetables and fruits, and they are not afraid of the lack of dietary fiber. However, with the improvement of living standards, the degree of food refinement is getting higher and higher, and the proportion of animal food is greatly increased. The heat production ratio of dietary fat in some big cities has increased from 20% ~ 25% several decades ago to 40% ~ 45% at present, while the intake of dietary fiber has obviously decreased. The so-called "life is getting better and better, and there is less and less fiber".