From Barry Groves:
"Gallstones are formed when the gall bladder is not emptied on a regular basis. In people who continually resort to low-fat diets, bile is stored for long periods in the gall bladder — and it stagnates. In time — and it is really quite a short time — a 'sludge' begins to form. This then coagulates to form small stones which then become bigger. The speed with which this happens was dramatically demonstrated in a trial at several American University hospitals. None of the subjects had any sign of gall bladder disease at the start of the study. However, after only eight weeks of low-fat dieting, more than a quarter had developed gallstones. Where they were fed intravenously, half developed gall bladder sludge after three weeks, and all had developed it by six weeks. Nearly half of those who developed sludge also formed gallstones.
The pain that someone with gallstones gets is when these are passed through the bile duct with the bile in response to a fatty meal and get stuck. Bile is then unable to enter the bowel, leading to biliary colic and its related symptoms: poor digestion, bloating, burping, flatulence, nausea, vomiting and sometimes jaundice.
So, it is a low-fat diet which causes the gallstones, but it is eating a high-fat diet that makes them apparent. If you eat a low-fat diet and never eat fat again, then you won't get the pain, even though the stones are there. The doctor who says that the gallstones are caused by high-fat is actually saying that the symptoms are caused by the fat.
If someone suffers from gallstones, a low-fat diet 'prevents' the symptoms, so doctors often suggest such a diet. But it makes the cause of the symptoms (gallstones) worse. Doctors are often loath to operate to remove the stones, so just preventing you knowing about them seems to them to be a good compromise — despite the fact that you will then be miserable and hungry as a result!"