New microbial genes responsible for bile acid conversion is a major step forward for gut health As the owner of a human body, you're carrying trillions of microbes with you everywhere you go. These microscopic organisms aren't just hitching a ride; many of them perform essential chemical reactions that regulate everything from our digestion to our immune system to our moods. One important set of reactions relates to fat absorption via bile acids. Our livers make these acids to help digest fats and fat-soluble vitamins as they travel through the small intestine. Near the end of the small intestine, microbes convert the acids into new forms, which can either be beneficial or harmful.