How Does WLS Affect Key Hormones in Your Gut?

Article By: Maria Tucker, MPH, RDN, LDN, CDCES

Maria Tucker is a Registered Dietitian and Certified Diabetes Educator with over 20 years of experience assisting patients with diabetes, obesity, and nutrition-related conditions. Maria is also the Founder of, a site dedicated to healthy recipes and kitchen shortcuts.

Obesity is a very serious epidemic all over the world associated with increased risk of type 2 diabetes, joint problems, high blood pressure, and heart disease among others. The World Health Organization (WHO) defines obesity as the accumulation of excessive fat harmful to health. It has been estimated that by 2030, more than 1 billion adults will suffer from obesity. Bariatric surgery has been an effective treatment for obesity and improving metabolic syndrome and risk of certain chronic diseases.

It is widely documented that bariatric surgery results in substantial weight loss by restricting GI tract volume and the resulting metabolic changes in the body. How bariatric surgery results in metabolic changes is not completely understood, but it is thought to likely be due to changes in secretion of gut hormones and potentially changes in the lining of the GI tract.

The National Institutes of Digestive and Diabetes and Kidney Diseases (NIDDK) describes the GI tract as a series of hollow organs joined in a long, twisting tube comprised of the mouth, esophagus, stomach, small intestine, large intestine, and anus. The liver, pancreas, and gallbladder are the solid organs of the digestive system. Several hormones are secreted by these organs which help digest and absorb nutrients and calories from the food we eat.

Two hormones produced in the stomach, gastrin and ghrelin, are believed to be affected by bariatric surgery. Gastrin, which stimulates the release of gastric acid and promotes satiety, has been shown in some evidence to be decreased after gastric bypass. Ghrelin, is a hormone that stimulates hunger and increases appetite. It also helps regulate use of energy. Some studies have shown ghrelin to be decreased after gastric bypass, but other studies showed this hormone to be increased in both humans and rodents after gastric bypass. Sleeve gastrectomy has been associated with decreased ghrelin since it is produced in the part of the stomach removed during sleeve gastrectomy.

In the duodenum or first part of the small intestine, cholecystokinin (CCK), is secreted. CCK stimulates digestion of proteins and fat by causing the release of digestive enzymes from the pancreas and bile from the gallbladder. This action slows movement of food out of the stomach and helps suppress hunger. A small study in 2015 showed that sleeve gastrectomy enhanced CCK levels and increased satiety. Another hormone produced in the small intestine, Peptide YY (PYY), is known to delay gastric emptying, decrease postprandial insulin production and more importantly, regulate appetite, promoting satiety. Some studies have shown PYY to be increased after bariatric surgery.

The pancreas, specifically its beta cells, releases insulin, a hormone that helps regulate blood sugar by promoting absorption of glucose from the blood stream to the liver (for storage) and to other tissues such as the skeletal muscles where it is needed for energy. More and more studies show that the function of the beta cells improves after sleeve gastrectomy and gastric bypass resulting in a more rapid insulin response. It is well documented that type 2 diabetes progression is reduced after bariatric surgery.

These are just a few of the hormones that are being studied in relation to bariatric surgery. Other hormones, like Glucagon-Like Peptide 1 (GLP-1), which enhances satiety and increase insulin production and sensitivity, has been shown to be increased after sleeve gastrectomy and gastric bypass.

The effect of bariatric surgery on hormones decreasing appetite and suppressing hunger is of benefit to bariatric surgery patients; however, it can lead to skipping meals and snacks resulting in inadequate calorie intake which can result in stalled weight loss and potentially malnutrition. There is no doubt that bariatric surgery has positive effects on the hormones produced by our digestive system regulating appetite and satiety, but as we often see at the end of articles, more research is needed to further understand them.

BariMelts provides general recommendations, not to be construed as medical advice. Please consult your doctor.

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