The Roux-en-Y gastric bypass (RYGB) is a well-accepted tool for the treatment of obesity and compared to conventional weight loss methods (e.g. diet and exercise) and other weight loss surgeries (e.g. gastric banding), it results in considerable weight loss that is maintained long-term. Although successful, the mechanisms for weight loss are not completely understood and it is thought that favorable changes in several gastrointestinal (GI) hormones and satiety play a role. Previous research suggests that the satiety promoting hormones, GLP-1 and PYY increase after RYGB, while the orexigenic GI hormone ghrelin and the adipocytokine leptin decrease. These changes generally occur before substantial weight loss, suggesting that a component of the surgery is responsible. Subjective satiety has also been reported to increase after RYGB, likely because of changes in the GI hormones and due to the reduced stomach capacity after surgery, but it is not clear if this alteration is maintained long-term. In addition, it is currently not well understood what effect different macronutrients have on the GI hormones and subjective satiety in the post-RYGB patient population. From a clinical perspective, there is a need for understanding how various macronutrients affect these parameters, as this is useful information that might allow for improved dietary treatment recommendations after RYGB. In the first study, changes in the GI hormones and leptin were evaluated after RYGB. This study also assessed if the GI hormones differed after a short-term dose of protein (PRO-BEV) or fat (FAT-BEV). GLP-1, PYY, ghrelin, and leptin were assessed in 16 women before and at 2, 6, 26, and 52 weeks after RYGB. GLP-1 increased at Weeks 6 and 52 in the FAT-BEV group compared to before surgery. PYY remained elevated at Week 52 in the FAT-BEV group. Ghrelin decreased at Weeks 2, 6, and 52 in the PRO-BEV group compared with Pre-RYGB. Ghrelin was lower in the PRO-BEV group compared with the FAT-BEV group at Week 6. Fasted leptin decreased at all visits in both groups and was lower in the FAT-BEV compared with the PRO-BEV group at Week 52. In the second study, subjective satiety was evaluated before and after RYGB. This study also assessed if subjective satiety differed after a dose of either protein or fat and investigated if subjective satiety, the GI hormones, and/or weight loss are related. Subjective satiety was not different between treatment groups. Satiety increased at the Week 2 visit compared to before surgery. Satiety scores had generally returned to Pre-RYGB levels after the Week 6 visit. Subjective satiety was not related to any of the GI hormones. Weight loss was unrelated to subjective satiety and the GI hormones. Results from these studies indicate that favorable changes occur after RYGB for the GI hormones/leptin and subjective satiety; some differences were evident soon after surgery (ghrelin, leptin, subjective satiety) while others were maintained long-term (GLP-1, PYY, ghrelin, leptin). In response to a short-term stimulus, protein suppressed ghrelin and fat stimulated GLP-1 and PYY. Although we did not find a difference in subjective satiety between beverage groups, assessment of the macronutrient effect on satiety is a novel analysis in this patient population, and further work is needed to better define the post-RYGB nutrition recommendations. Continued research in this area that attempts to better understand dietary components that could ultimately lead to successful weight loss/maintenance is needed for proper nutrition care after RYGB.
University of Minnesota Ph.D. June 2012. Major:Nutrition. Advisor: Carrie Penland Earthman. 1 computer file (PDF); xi, 129 pages, appendices A-B.
Beckman, Lauren Marie.
Changes in gastrointestinal hormones, leptin, and satiety after gastric bypass surgery.
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