Does reduction in gastric acid secretion in bariatric surgery increase diet-induced thermogenesis?

Patients who have undergone gastrectomy 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 investigated 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.

22 volunteers without symptoms from the upper gastrointestinal tract were studied. Gastric pH was measured and resting energy expenditure (MREE), using indirect calorimetry, was determined before and 8 hours after consumption of a standard meal. Parameters were measured again after 2 months administration of proton pump inhibitors in all volunteers.

Although significant reduction of gastric acid secretion occurred (p < 0.01), following administration of proton pump inhibitors, the fasting and postprandial MREE remained unchanged (p > 0.05).

The reduction in gastric acid secretion does not increase the energy requirements for digestion of foods and thus is neither the mechanism responsible for the increased weight loss observed after RYGBP or BPD, nor the explanation for the lean appearance of gastrectomized patients.