The gallbladder stores bile, and concentrates it holding ready for digestion. The gallbladder can store up to one cup of concentrated bile . Shortly after eating a meal, the gallbladder squeezes and its bile is released back into the bile duct, and then into the gut. Bile helps fat digestion, and some bile is reabsorbed, returning to the liver, whilst the waste materials within it are eliminated from the body in the stools - which is why they are usually coloured brown. Around one in ten people have gallstones, most commonly as they get into mid-life.
Women develop gallstones more commonly than men and at a younger age.
Gallstones vary in size and may be as small as sand grains or as large as a plum. The gallbladder may develop a single, often large, stone or many smaller ones, even several thousand. This can be encouraged by a combination of factors, including inherited body chemistry, body weight, sluggish gallbladder movement, and perhaps diet. Some proteins in bile can promote or inhibit cholesterol crystallisation. Obesity is a major risk factor for gallstones, with a large clinical study showing that even being moderately overweight increases the risk of developing gallstones, probably because it causes excess cholesterol in bile, low bile salts, and decreased gallbladder emptying.