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FROM THE EDITOR’S DESK.... DIABETES AND BARIATRIC SURGERY Insulin sensitivity for glucose disposal in individuals with normal glucose tolerance is impaired above a body mass index of 27 kg/m2 or above an ideal body weight of 120%.1,2 Impaired glucose tolerance accompanied by hyperinsulinemia is well recognized in obesity.3,4 "Nondiabetic" massively obese individuals have impaired glucose tolerance on 6-hr glucose tolerance tests, evidenced by high peak and delayed fall of plasma glucose and by increased area under the glucose tolerance curve.5 All operations for morbid obesity are rapidly effective for Type 2 diabetes. 5-9 The jejuno-ileal (JI) bypass produced immediate resolution of Type 2 diabetes.5 The postoperative oral glucose tolerance curve was flat due to the malabsorption. Plasma insulin levels fell rapidly to normal after surgery, and there was an up-regulation of insulin receptors. After 30% weight loss following JI bypass, both glucose and plasma insulin response to I.V. glucose tolerance tests returned towards normal. After vertical banded gastroplasty (VBG) in diabetics, fasting plasma glucose returns towards normal before discharge from hospital and before notable weight loss.6,7 However, the glycosylated hemoglobin (HbA1C), which reflects prior hyperglycemia, remains elevated for up to 3 months postoperatively. Immediately postoperatively, exogenous insulin is usually given by I.V. drip in Type 2 diabetics, during the stress phase and while peripheral I.V. fluids are normally administered. When the I.V. is discontinued, no insulin infusions are generally needed in these patients with poor veins, and no oral hypoglycemic agent is usually required. 6 After VBG, because of the narrow edematous channel, oral intake is quite limited and variable. A specific caloric intake cannot be guaranteed orally, and patients are allowed to exhibit occasional mildly elevated plasma glucose in the days following gastric restriction. Average calorie counts by the 4th week after VBG were 600 kcal/day, rising to 1100 kcal at 1 year.6 During the period of liquid beverages postoperatively, diet drinks can be distinguished from their sugar-containing counterparts by the use of urineglucose dip-sticks, which change color when exposed to glucose but show no color change with diet beverages.10 Later following bariatric surgery, the weight loss maintains normal plasma glucose levels. The Roux-en-Y gastric bypass (RYGBP) is very effective for diabetes due to the tiny proximal gastric reservoir and the decreased carbohydrate intake to avoid early dumping. 11 An additional advantage of RYGBP is postulated to be bypass of the hormonally active gastric antrum, duodenum and proximal jejunum (the insulinenteric axis which modulates glucose metabolism and insulin action).8 In the longer term, weight reduction itself fosters insulin sensitivity and improves glycemic control. MacDonald and co-workers12 found in a long-term study of Type 2 diabetics after RYGBP (mean follow-up 9 years) that the mortality was 9%, compared with 28% in non-operated diabetic controls. The improvement in mortality in the RYGBP group was mainly due to a decrease in cardiovascular deaths. 12 Elevated free fatty acid levels lead to insulin resistance and inhibition of glucose metabolism.1,9,13 In patients after biliopancreatic diversion (BPD) with almost ideal body © FD-Communications Inc.

weight, post-obese individuals showed similar insulin sensitivity to normal-weight controls and a normal plasma glucose profile, with normalization of insulin response to a glucose load.9 After BPD, insulin resistance and diabetes reverse before significant weight loss has occurred, related to reduction of plasma triglyceride and circulating free fatty acids, due to marked decrease in lipid absorption.13 Insulin resistance with impaired glucose tolerance has been postulated to be related to excess truncal or central body fat. Whether this corresponds to fat in the abdominal pannus or viscera is unclear. Studies of abdominal lipectomy, before and after removing the large abdominal overhanging pannus, found a decrease in plasma insulin but no change in glucose levels.14 There is type of adult-onset diabetes (not Type 2) which does not require obesity as an etiologic factor. This diabetes is associated a subnormal plasma insulin, and represents about 10% of adult diabetics. These individuals can be normal weight, overweight or underweight at the time that their diabetes is discovered. However, their diabetes behaves like Type 1, and they soon require insulin. A bariatric operation in these individuals could be devastating. In this issue, Nedelnikova et al.(page 372) report a small study suggesting that diabetes itself may be a predictor of low weight loss following gastric banding. Mervyn Deitel, MD, Toronto References 1. Campbell PJ, Gerich JE. Impact of obesity on insulin action in volunteers with normal glucose tolerance: demonstration of a threshold for the adverse effect of obesity. J Clin Endocrinol Metab 1990; 70: 1114-18. 2. Sanderson I, Deitel M. Insulin response in patients receiving concentrated infusions of glucose and casein hydrolysate for complete parenteral nutrition. Ann Surg 1974; 179: 387-94. 3. Modan M, Karasik A, Halkin H et al. Effect of past and concurrent BMI on prevalence of glucose tolerance and type 2 (noninsulin-dependent) diabetes and on insulin response. Diabetologia 1986; 29: 82-9. 4. Kolterman OG, Insel J, Saekow M et al. Mechanisms of insulin resistence in human obesity. J Clin Invest 1980; 65: 1272-84. 5. Sanderson I, Deitel M, Bojm MA. Handling of glucose and insulin response before and after weight loss with JI bypass. JPEN 1983; 7: 274-6. 6. Deitel M, Sidhu PS, Stone E. Effect of vertical banded gastroplasty on diabetes in the morbidly obese. Obes Surg 1991; 1: 113-4 (abstr). 7. Jensen K, Mason EE, Scott DH. Changes in the post-operative hypoglycemic and anti-hypertensive medication requirements in morbidly obese patients after VBG. Obes Surg 1991; 1: 114 (abstr). 8. Pories WJ. Why does the gastric bypass control Type II diabetes? Obes Surg 1992; 2: 303-13. 9. Castagneto M, De Gaetano A, Mingrone G et al. Normalization of insulin sensitivity in obese patients after weight reduction with biliopancreatic diversion. Obes Surg 1994; 4: 161-8. 10. Ralph-Edwards A, Deitel M, Deitel FH. Diet Coke or not? Obes Surg 1992; 2: 277. 11. Smith-Sherman C, Edwards CB, Goodman GN. Changes in diabetic management after Roux-en-Y gastric bypass. Obes Surg 1996; 6: 345-8. 12. MacDonald JR, Long SD, Swanson MS et al. The gastric bypass reduces progression and mortality of non-insulin dependent diabetes. J Gastrointest Surg 1997; 1: 213-20. 13. Mingrone G, De Gaetano A, Greco AV et al. Reversibility of insulin resistence in obese diabetic patients: role of plasma lipids. Diabetologia 1997; 40: 599-605. 14. Cazes L, Deitel M, Levine R. Effect of lipectomy on lipid profile, glucose handling, and blood pressure with truncal obesity. Obes Surg 1996; 6: 159-66.

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