Normal intestinal flora is the patron saint of human health and is an essential microbiota. Their main contributions to human health are in the following four areas: 1, help digest food and absorb nutrients (including protein, sugar, fat, iron, calcium and vitamin D, synthesize vitamins B, C, K, niacin and folic acid, etc.), and maintain normal intestinal motility. 2, promote the immunity of the organism, by bifidobacteria, lactobacilli and other membrane flora composed of occupancy protection, production of bacteriocins, organic acids, hydrogen peroxide and other substances, block or inhibit pathogenic bacteria or conditional pathogenic bacteria invasion of the intestinal mucosa to produce non-specific immune effect, intestinal flora as antigens can stimulate and promote the development of the immune system and the maturation of its function, so that the body to gain resistance to many pathogenic bacteria and their toxins. Exert specific immune effect. 3.In the case of flora balance, inhibit the occurrence and development of tumor. Bifidobacterium and other beneficial bacteria can degrade amine nitrite into nitrite and amine, and play a role in cancer inhibition, while E. coli, Clostridium difficile, Enterococcus and Bacillus can promote the combination of nitrite and amine in food into amine nitrite which has strong carcinogenic effect. Therefore, whether the intestinal flora is cancer-promoting or cancer-suppressing depends on which flora are dominant. In a healthy state, the cancer-inhibiting flora is dominant, so it mainly plays the role of cancer inhibition. 4. In the case of balanced flora, intestinal flora can reduce the absorption of cholesterol, reduce the concentration of endotoxin in the blood, and have anti-aging effects.