Gastric bypass surgery is associated with near-normal insulin suppression of lipolysis in nondiabetic individuals

We hypothesized that individuals who have undergone gastric bypass have greater insulin sensitivity that obese subjects but less compared with lean. We measured free fatty acid (FFA) and glucose kinetics during a two-step, hyperinsulinemic euglycemic clamp in nondiabetic subjects who were 38 ± 5 mo post-gastric bypass surgery (GB; n = 15), in lean subjects (L; n = 15), and in obese subjects (O; n = 16). Fasting FFAa were not significantly different between the three study groups but during both doses of insulin were significantly higher in O than in either GB or L. The effective insulin concentration resulting in half-maximal suppression of FFA was similar in L and GB and significantly less in both groups compared with O. Glucose infusion rates during low-dose insulin were not significantly different in GB compared with either L or O. During high-dose insulin, glucose infusion rates were significantly greater in GB than in O but less than in L. Endogenous glucose production in GB was significantly lower than O only during low dose of insulin. We conclude that gastric bypass is associated with improvements in adipose tissue insulin sensitivity to levels similar to lean, healthy persons and also with improvements in the response of glucose metabolism to insulin. These changes may be due to preferential reduction in visceral fat and decreased FFA availability. However, some differences in insulin sensitivity in GB remain compared with L. Residual insulin resistance may be related to excess total body fat or abnormal lipolysis and requires further study.