Alterations in body composition following intestinal bypass for morbid obesity.

The efficacy of the jejunolieal bypass operation, performed as a weight-reducing procedure in the morbidly obese patient, was assessed by measurements of body composition. In 20 patients measurements were performed by multiple isotope dilution, before and following jejunoileal bypass. Prior to bypass the excess body weight was due primarily to an increase in body fat (BF), which accounted for 52 percent of body weight. The nonfatty component of body composition, the lean body mass, although slightly increased in size, was essentially normal. Two distinct patterns were observed following bypass. In 12 patients followed for 8.4 +/- 1.5 months, there was a 21 percent decrease in body weight, resulting entirely from a loss of BF. The total exchangeable potassium and intracellular water volume, both measures of the body cell mass (BCM), were unchanged. In the second group of eight patients followed for 13.9 +/- 2.1 months, the mean body weight decreased by 27 percent or 38.8 Kg., due to a 26.6 Kg. reduction in BF and a 13.0 Kg. decrease in the BDM. This was accompanied by a relative expansion of the extracellular mass. As a result, the mean Nae/Ke ratio increased significantly (p less than 0.05) from a normal prebypass value of 0.95 +/- 0.7 to 1.46 +/- 0.11 following bypass. Thus in eight of the 20 patients following jejunoileal bypass, there was an undesirable loss of BCM with a relative expansion of extracellular supporting component of body composition, a pattern characteristic of malnutrition.