Biliary and urinary calculi: pathogenesis following small bowel bypass for obesity

Of 93 patients with small bowel bypass for massive exogenous obesity, three developed calcium oxalate urinary calculi, four stones in their gallbladder, and one developed both gallstones and urinary calculi during a mean follow-up period of 17.6 plus or minus 9.0 months. The urinary oxalate excretion increased from 21.6 to 67.8 mg/24 hours (P smaller than .001); simultaneously, the urinary output decreased from 1,775 to 1,101 ml/24 hours (P smaller than .001). Postoperatively, there was a significant increase in the rate of bile salt synthesis from 1.6 to 4.9 gm/day (P smaller than .02) and in the bile sale glycine/taurine ratio from 4.6 to 6.8 (P smaller than .05). It is suggested that the postbypass increase in the biliary glycine/taurine ratio, with its consequent decrease in the zeta potential of the micelles in bile, is at least partly responsible for the increased incidence of cholelithlasis. The pathogenic basis for the increased incidence of urinary calculi is hyperoxaluria, which is probably related to an increased bile salt and glycine synthesis.