One of the many chemicals that your gut bacteria produce is butyrate, a short chain fatty acid. Butyrate has many uses in your body, including feeding other gut bacteria, feeding the epithelial cells in your intestines, has anti inflammatory properties, used as a neurotransmitter, and encourages the production of growth hormones. Your gut bacteria also produce a number of other chemicals, including many vitamins.
There are at least 400 different species living in a healthy person's gut (it's difficult to define a species, since they transfer dna between themselves.) Many of these we haven't been able to successfully grow in a lab. Their primary food is resistant starch, which is starch that your small intestines can't split apart and absorb. There are a number of different types of resistant starch, which basically comes down to how the chains of glucose and fructose molecules are arranged. Different bacteria prefer different types of resistant starch, and thus you can majorly influence your biome just by changing your diet. There's a special diet called FODMAP which supposedly helps with IBS and related diseases. I also think that a number of fad diets main benefit is influencing your gut bacteria.
There are at least 400 different species living in a healthy person's gut (it's difficult to define a species, since they transfer dna between themselves.) Many of these we haven't been able to successfully grow in a lab. Their primary food is resistant starch, which is starch that your small intestines can't split apart and absorb. There are a number of different types of resistant starch, which basically comes down to how the chains of glucose and fructose molecules are arranged. Different bacteria prefer different types of resistant starch, and thus you can majorly influence your biome just by changing your diet. There's a special diet called FODMAP which supposedly helps with IBS and related diseases. I also think that a number of fad diets main benefit is influencing your gut bacteria.