I have tried without success to find more information on this study which was done in 1984 but have been unsuccessful, but it does show that ingesting pectin led to a 52% regression in Gallstones in hamsters, and this may offer proof and explain why some people have flushed out stones by fasting on apples without doing a liverflush.
Experientia. 1984 Apr 15;40(4):350-1. Related Articles, Links
Effect of pectin and cellulose on formation and regression of Gallstones in hamsters.
Kritchevsky D, Tepper SA, Klurfeld DM.
Male Syrian hamsters were fed a lithogenic diet containing 7% cellulose or 4.2% pectin. After 50 days, pectin was 76% and cellulose 64% less lithogenic than the control diet. Hamsters fed the control diet for 50 days were maintained on that diet for another 50 days or fed diets containing cellulose or pectin. There was a 52% increase in gallstone incidence in hamsters continued on the control diet and a 9% increase in those on cellulose. Pectin promoted regression of Gallstones (by 52%).