Bariatric surgery doesn’t only cause dramatic weight loss—the procedure itself has profound metabolic effects, according to studies published in the September issue of Gastroenterology.
Two types of bariatric surgery are most effective therapies for sustained weight loss in obese patients. In Roux-en-Y gastric bypass (RYGB), a gastric pouch drains into the mid-jejunum and pancreaticobiliary flow is diverted to the distal jejunum. So, ingested food bypasses most of the stomach, the entire duodenum, and a short portion of jejunum. Alternatively, in vertical sleeve gastrectomy (VSG), 80% of the stomach is removed but intestinal anatomy is unaltered (see figure).
Patients that undergo these procedures usually lose more than 60% of excess body weight. Furthermore, more than 80% with type 2 diabetes acquire normal fasting glucose concentrations and levels of insulin sensitivity, often before any substantial weight loss occurs. Researchers compared the effects of these surgeries, as well as dieting, in rats.
Margaret Stefater and colleagues found that plasma levels of lipids decrease greatly after bariatric surgery, which might explain why this procedure reduces the risk for cardiovascular disorders. The reduction in lipid resulted from the surgery itself, rather than changes in eating habits of the rats; the drop in plasma levels of lipid after VSG was weight-independent and caused by attenuated postprandial triglyceride production in the intestine. High plasma levels of lipid cause atherosclerosis, particularly in obese patients; Stefater et al. propose understanding the mechanisms by which VSG lowers lipid levels could lead to new therapies for atherosclerotic disease.
But is RYGB or VSG a better method for weight loss? Adam Chambers et al. compared the effects of each surgery on metabolic effects in obese rats, and found that both produce weight loss-dependent increases in overall insulin sensitivity. However, they also produce weight loss-independent increases in hepatic insulin sensitivity and release, as well as levels of glucagon-like peptide-1 (GLP)-1. GLP-1 is an intestinal hormone released in response to nutrients that regulates glucose levels; Chambers et al. found it was required for the beneficial effects of each procedure on levels of glucose after eating. The increases observed in GLP-1 did not result from reduced body weight or caloric intake—rats that lost weight on a control diet had no changes in GLP-1or insulin release.
So these surgical procedure themselves, beyond the resulting weight loss, have beneficial effects for obese patients. Chambers et al. conclude that RYGB and VSG produce similar outcomes in terms of effects on food intake, body weight, and resolution of type 2 diabetes. They propose that because VSG is a technically simpler operation and requires less recovery time than RYGB, and because VSG is not associated with the malabsorption of micronutrients, it could be the best choice for many patients.
In an accompanying editorial, Rexford Ahima and Ahlam Sabri state that although the results from Stefater et al. showed that VSG decreased postprandial triglyceride levels, there are no known mechanisms that regulate intestinal triglyceride secretion—it will be important to determine whether VSG alters intestinal triglyceride secretion through gut hormones. Further studies are needed to determine whether VSG and RYGB differentially inﬂuence intestinal transit and neural and hormonal mechanisms.
More Information on Bariatric Surgery:
- The American Society for Metabolic and Bariatric Surgery
- National Library of Medicine Website on Weight Loss Surgery
- The Mayo Clinic Website on Weight Loss Surgery
Read the articles online. These articles have an accompanying podcast.
Stefater MA, Sandoval DA, Chambers AP, et al. Sleeve gastrectomy in rats improves postprandial lipid clearance by reducing intestinal triglyceride secretion. Gastroenterology 2011;141:939-949.e4.
Chambers AP, Jessen L, Ryan KK, et al. Weight-independent changes in blood glucose homeostasis after gastric bypass or vertical sleeve gastrectomy in rats. Gastroenterology 2011;141:950–958.
Read the accompanying editorial:
Ahima RS, Sabri A. Bariatric Surgery: Metabolic benefits beyond weight loss. Gastroenterology 2011;141:793–795.