Gallbladder motility and lithogenesis in obese patients during diet-induced weight loss

Obesity and weight loss are important risk factors for gallstone developmen t. The mechanisms involved are unknown. We prospectively studied changes in gallbladder (GB) emptying and bile composition during weight loss. We stud ied 12 alithiasic obese subjects who entered a six-month diet program (800- 1200 kcal/day, 26 g fat/day). As controls we evaluated 12 healthy nulliparo us nonobese young women. GB volumes were studied by ultrasonography (fastin g volume, GBFV; residual volume after a liquid meal, GBRV) at entry and aft er 4 and 20 weeks of dieting. Bile acid pool size, biliary lipid compositio n, presence of cholesterol crystals, and nucleation time were also studied. Of 12 obese subjects studied (mean BMI 35.1 kg/m(2)), 10 remained in the p rogram for six months, but only six completed the entire study protocol, ob taining a significant weight loss (BMI: 31.2 kg/m(2), P < 0.001). GBFV was greater in obese subjects than in nonobese controls (27.5 +/- 10.7 vs 11.7 +/- 6 mi; P < 0.05). GBRV and GB emptying curves were similar in both group s and did not change during weight loss. The obese subject who developed ga llstones (1/10) was the only one who had cholesterol crystals in bile and a sluggish initial GB emptying. In conclusion: (1) obese subjects had a grea ter GBFV than controls; however, the GB emptying was adequate. (2) During w eight loss we did not observe significant changes in GB kinetics or the bil e parameters studied. (3) We observed a relatively low frequency of gallsto ne formation, which can be explained by a high fat content of the diet (26 g/day) and by the adequate GB emptying of our group of patients. (4) An abn ormal GB contractility and cholesterol crystals in bile could be considered premonitory to gallstone formation.