Role of caloric intake in the weight loss after jejunoileal bypass for obesity.

Sixty-five patients were studied prospectively after jejunoileal bypass for obesity. Dietary intake pre- and postoperatively was measured either directly by weighing food or by a research dietary history. Of 65 measurements, 59 were made at least 6 months after operation, when over 75% of weight loss had been achieved. Fat absorption was measured in 42 of the patients. The entire group ate fewer calories (mean +/- SE = 2595 +/- 135) postoperatively than preoperatively (mean +/- SE = 3261 +/- 138). This difference was highly significant (P less than 0.001). Forty-eight patients ate less after their operation. The caloric deficit calculated from the observed weight loss could be accounted for entirely by the estimated decrease in intake in 22 of the 48 patients who ate less postoperatively. Moreover, measured fat malabsorption accounted for only 31% of the observed weight loss in those who ate more postoperatively and 21% in those who ate less. We conclude that a decrease in caloric intake, along with malabsorption, is an important factor in the long term postoperative weight loss (1-9 months) after jejunoileal bypass for obesity.