It is estimated that in human body, the weight of microorganisms accounts for more than half of the wet weight of intestinal contents, the number of microbial cells even exceeds 10 times of cell account of the human body,

Under normal circumstances, human gastrointestine contains about 1000 kinds of microorganisms, the number of which reaches 1011-1012 cfu/g.
Overall, the composition of microbiome is correlated with our nutrition, health and even psychology.

Some metabolic diseases, such as obesity, are closely linked to the imbalance of intestinal flora.
Bifidobacterium and Lactobacillus are the main probiotic species in the human body, covering more than 200 types of probiotics,

Many of these beneficial strains are widely used in fermented food, some are even used in cosmetics, medicines, etc.
In China, the probiotics permitted to be used in food is listed in the Notice of Ministry of Health Ministry: http://samr.cfda.gov.cn/WS01/CL1975/228275.html