Bile is a fluid produced by the liver to help digest food. It is a mixture of cholesterol, fats, and other substances. Changes in bile, such as too much cholesterol, can cause bile to crystallize and form gallstones. Some research suggests that types of fat in the diet may affect a person's chance of developing gallstones. For example, diets high in saturated fat may promote gallstone formation, whereas diets high in unsaturated and monounsaturated fats, which together are called cis unsaturated fats, may make gallstones less likely.