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. The more obese a person is, the greater his or her risk is of developing gallstones. Several studies have shown that women with a BMI of 30 or higher have at least double the risk of developing gallstones than women with a BMI of less than 25. But researchers believe that in obese people, the liver produces too much cholesterol. The excess cholesterol leads to supersaturation in the gallbladder.