Explain three benefits that humans gain from "hosting" the microbial community of the human gut

1. Normal flora in the human gut can help digestion of certain product. One of the examples would be stercobilin from bilirubin cycle.
2. The microbial community can decrease infection chance because it will cause the pathogen that enters intestine to grow slower.
3. The microbes also can provide some nutrition like vitamins B and vitamin K.