Here is from atkins website:

http://atkinscenter.com/Archive/2001/12/18-292461.html

Fallacy: Atkins is high in fat, and we all know that fats cause gallbladder disease.
Fact: There is now overwhelming scientific evidence that gallstones (responsible for more than 90 percent of gallbladder disease are formed when fat intake is low. In a study that examined the effects of a diet that provided 27 grams of fat per day, gallstones developed in 13 percent of the participants9. The reason is that the gallbladder will not contract unless fat is taken in, and if it doesn't contract, a condition called biliary stasis develops and the bile salts crystallize into stones. Our gallbladders need to be kept active to prevent stone formation.

It is not uncommon to find gallstones in people who are obese, although the gallstones may not be causing discomfort. People with existing stones may, however, have trouble with high-fat meals. If you are one of these people you may have to slowly increase the level of fat you eat according to your own tolerance—meaning, how you feel. Remember, gallstones are not formed overnight. So anyone who tells you they started doing Atkins and two weeks later developed gallstones doesn't fully understand the medical situation.