Bone mineral content before and after intestinal bypass operation in obese patients.

With the aim of investigating bone mineral loss after intestinal bypass operation, bone mineral content (BMC) was measured by two-dimensional scanning photon absorptiometry on the distal part of the forearm in 23 consecutive patients who had undergone intestinal bypass operation for obesity. Eleven patients (group 1) were investigated before and 12 months after operation, and 12 (group 2), who had been operated on 2-7 years earlier, were investigated two times at an interval of 12 months. No patient received therapeutic calcium or vitamin D supply. The predominant biochemical findings postoperatively were decreased serum values of calcium, magnesium, albumin, and total protein; there was no change in inorganic phosphate or alkaline phosphatase. Mean BMC was normal in both groups postoperatively as well as in group 1 before operation; there was no significant change in mean BMC during 12 months of observation. However, in BMC measurements on extremely obese subjects, a correction for the excessive fat layer on the forearm was necessary because of different attenuation properties of fat and soft tissues. Neglect of this problem will give a systematic underestimation of BMC, and may lead to false conclusions in cross-sectional as well as longitudinal studies.