Cholesterol crystallization in gall-bladder bile of pigs given cholesterol-beta-cyclodextrin-enriched diets with either casein or soyabean concentrate as protein sources

Cholesterol precipitation from supersaturated bile is the earliest and dete rminant step in the formation of cholesterol gallstones, which is thought t o be diet-dependent. Bile composition, appearance and growth of cholesterol crystals were studied in fresh gall-bladder biles from pigs adapted to fou r different protein-containing diets over 3 weeks: 160 g dietary protein/kg as casein (C16; n 6), or as soyabean-protein concentrate (S16; n 6), or a mixture of both protein sources (casein-soyabean protein, 70 : 30, w/w) (CS 16;n 6), or 320 g of the mixed protein/kg (CS32; n 6). Moreover, all four d iets contained 3 g cholesterol/kg and 50 g beta-cyclodextrin/kg as modifier s of bile composition towards cholesterol pro-crystallization. Cholesterol precipitation was most active after the high-protein diet, CS32, and the ca sein diet, C16, and lowest after the soyabean-protein diet, S16. It was int ermediate after the mixed diet, CS16, but still much lower than in the form er two groups. These diet-induced variations were suggested to be mediated through modifications in the biliary profile of bile acids, whereas all oth er biliary constituents studied were essentially unchanged. The fasting lev el of plasma cholesterol was lowest in both 160 g protein/kg diets containi ng soyabean protein (S16 and CS16), highest for the high-protein diet CS32, and intermediate for the C16 diet. These results should encourage clinical studies on the effect of soyabean protein, or other vegetable proteins, fo r primary or recurrence prevention of cholelithiasis at its earliest stage.