Bile contains substances called bile salts that act like natural detergents to break down fats in the food we eat. As food passes from the stomach into the small intestine, the gallbladder releases bile into the bile ducts. These ducts, or tubes, run from the liver to the intestine. Bile also helps eliminate excess cholesterol from the body. The liver secretes cholesterol into the bile, which is then eliminated from the body via the digestive system.
Most researchers believe three conditions are necessary to form gallstones.
First, the bile becomes supersaturated with cholesterol, which means the bile contains more cholesterol than the bile salts can dissolve. Second, an imbalance of proteins or other substances in the bile causes the cholesterol to start to crystallize. Third, the gallbladder does not contract enough to empty its bile regularly. Obesity is a strong risk factor for gallstones. For example, an obese woman who is 5 feet 4 inch tall and weighs 174 pounds has a BMI of 30.