Bariatric surgery works for weight loss & diabetes. But what’s really behind the success? Gut hormones.

Bariatric surgery is making headlines- just the other day the New York Times ran a story called Why Weight Loss Surgery Works When Diets Don’t, where someone said “Bariatric surgery is probably the most effective intervention we have in health care.” And indeed, it has proven it to be so. No one can deny the physical results- extreme, durable weight loss- up to 40% reduction in body weight after bypass. Then there are the metabolic improvements- normalizing blood sugar and putting type 2 diabetes into remission—which happened in 84% of patient’s after bypass in one study. And lets not forget about normalizing blood pressure and cholesterol, fatty liver, heart problems, acid reflux, arthritis, infertility, stress incontinence, and curing sleep apnea. And finally the mental benefits- post-bariatric surgery, people rated themselves healthier, less likely to report problems with mobility, pain, daily activities, social interactions and feelings of depression and anxiety. 

What drives these fabulous results? None of the published articles revealed the real reason these surgeries are working. The answer is— the gut-brain connection & gut hormones. 

Weight loss efforts are often defeated by the body’s thermostat that regulates body weight. Everyone has a genetically influenced level of fat that is defended by this control system and changes in body fat stores trigger changes in appetite and energy expenditure to resist weight change. This evolved to defend us against malnutrition and starvation.. but now is working against us. Because of this thermostat-- diet, exercise and medications only are successful at losing 5-10% of body weight… and re-gain is almost always expected. But with bariatric surgery you lose 40%! Bariatrics works despite this regulation—because it gets to a more basic principle-- altering gut hormones.

appetite regulation.jpg

Back to that ‘gut-brain axis’ again. Many hormones are secreted from the GI tract and contributes to regulation of energy balance and glucose homeostasis through interaction with the nervous system. The main players are peptide YY (PYY), glucagon-like peptide-1 (GLP-1) and ghrelin.


-  PYY &  GLP-1 are released after food intake and decrease appetite, increase satiety, slow gut motility and improve insulin sensitivity.

- GHRELIN is suppressed after a meal but when active, stimulates appetite, increases food intake and gut motility and decreases insulin sensitivity. When you purely calorie restrict, levels of ghrelin go WAY up.

What do we want? Tons of PYY & GLP-1 to decrease appetite and for GHRELIN to stay quiet. What does gastric bypass do? Increase PYY & GLP-1 and decreases GHRELIN.

No wonder it works!

Conclusion: It’s not the surgery per se that’s causing all of these fabulous weight loss and metabolic outcomes—it’s the gut hormones. And the good news is that you don’t have to undergo surgery to manipulate these hormones!  There are endoscopic GI procedures for weight loss and metabolic management available as well as medications such as GLP-1 agonists (Liraglutide, Exenatide, etc).