© FD-Communications Inc. Obesity Surgery, 12, 2002 399 Obesity Surgery, 12, 399-403 Background: Patients who have undergone gastrec- tomy for benign ulcer do not develop obesity. Furthermore, morbidly obese patients who undergo biliopancreatic diversion (BPD), Roux-en-Y gastric bypass (RYGBP) and vertical banded gastroplasty (VBG) plus truncal vagotomy, may lose more weight compared with patients who undergo VBG alone. A common characteristic of the above is the reduction of gastric hydrochloric acid secretion. We investi- gated whether reduction in gastric acid increases dietary- induced thermogenesis because of maldigestion of foods, and this may account for the greater weight loss in the above situations. Materials and Methods: 22 volunteers without symptoms from the upper gastrointestinal tract were studied. Gastric pH was measured and resting energy expenditure (MREE), using indirect calorime- try, was determined before and 8 hours after con- sumption of a standard meal. Parameters were mea- sured again after 2 months administration of proton pump inhibitors in all volunteers. Results: Although significant reduction of gastric acid secretion occurred (p<0.01), following adminis- tration of proton pump inhibitors, the fasting and postprandial MREE remained unchanged (p>0.05). Conclusions: The reduction in gastric acid secre- tion does not increase the energy requirements for digestion of foods and thus is neither the mecha- nism responsible for the increased weight loss observed after RYGBP or BPD, nor the explanation for the lean appearance of gastrectomized patients. Key words: Morbid obesity, bariatric surgery, metabo- lism, diet-induced thermogenesis, gastroplasty, gastric bypass, biliopancreatic diversion Introduction Operations currently in use for morbid obesity con- sist of restrictive, aiming at reduction of daily energy intake, such as vertical banded gastroplasty (VBG) and gastric banding (GB), malabsorptive where the intestinal energy absorption is less than the food energy intake, such as biliopancreatic diversion (BPD), and Roux-en-Y gastric bypass procedures (RYGBP) that produce weight loss by a combination of both mechanisms. 1 Although the mechanisms of weight loss result- ing from low energy intake, as produced by both low (800-1500 kcal/day) and very low (<800 kcal/day) calorie diets have been extensively stud- ied in humans, 2,3 the precise pathophysiological changes following the anti-obesity operations and the mechanisms of weight reduction and mainte- nance, are not yet entirely understood. 1,4 The present study is based on the universally accepted observation that patients who have under- gone gastrectomy for benign conditions do not develop obesity and remain lean for life. 5,6 Furthermore, morbidly obese patients that undergo BPD, 7 RYGBP 8 and VBG plus truncal vagotomy, 9 lose more weight compared with patients subjected to VBG. A common characteristic of all the above opera- tions is the reduction of gastric hydrochloric acid (HCL) secretion. We therefore investigated whether reduction in gastric acid secretion Reprint requests to: John Melissas, MD, 16 Sifaki Street, Heraklion, 71409, Crete, Greece. Fax: +30-81-542090; e-mail: melissas@med.uoc.gr Does Reduction in Gastric Acid Secretion in Bariatric Surgery Increase Diet-Induced Thermogenesis? John Melissas, MD, FACS; 1 Emmanuel Kampitakis, MD; 1 George Schoretsanitis, MD; 1 John Mouzas MD; 2 Elias Kouroumalis, MD; 2 Demetrios D. Tsiftsis, MD, FACS 1 Departments of 1 Surgical Oncology and 2 Gastroenterology, Heraklion University Hospital, University of Crete Medical School, Greece