Gallstones are pieces of solid material that form in the gallbladder.
Gallstones form when substances in the bile, primarily cholesterol and bile pigments, form hard, crystal-like particles. This is probably true because obesity tends to cause excess cholesterol in bile, low bile salts, and decreased gallbladder emptying. Very low calorie, rapid weight-loss diets, and prolonged fasting, seem to also cause gallstone formation. No clear relationship has been proven between diet and gallstone formation. They are twice as likely to develop gallstones than men.