Changes in serum lipids after gastric bypass surgery. Lack of a relationship to weight loss

Serum lipid levels were measured in 65 obese patients before and a mean of 13.4 +/- 0.2 months after gastric bypass surgery performed to facilitate weight reduction. The 58 women studied lost an average of 39.8 +/- 1.2 kg thereby reducing their mean body mass index from 41.9 +/- 0.7 to 26.8 +/- 0.6. Postoperatively, total cholesterol, LDL cholesterol, and triglyceride levels were significantly lower and HDL cholesterol levels significantly higher than preoperative values (for each of the four comparisons P less than 0.0001). Whereas before surgery 83 percent of the women had levels of total, LDL, or HDL cholesterol indicative of an increased risk of coronary heart disease, after surgery only 24 percent did so. Preoperative cholesterol abnormalities in the seven men were not as severe as were those in the women, and the men's postoperative cholesterol changes were not as marked. Correlations of the difference between pre- and post-operative weight and the difference between pre- and post-operative lipid levels showed that weight loss accounted at most for just 8 percent of the simultaneous lipid change. The data indicate that gastric bypass surgery for morbid obesity produces a favorable change in serum lipid profiles and suggest that the change is due primarily to factors other than the associated weight reduction.