Department of Research & Evaluation News

A Kaiser Permanente found that bariatric surgery reduced health care costs for adults with type 2 diabetes and obesity. The study was published in the Annals of Internal Medicine in February 2025.

“The study shows that both Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) help reduce health care costs for people with type 2 diabetes 5.5 years after surgery,” said the senior author of the study, Aniket Kawatkar, PhD, of the Kaiser Permanente Southern California Department of Research & Evaluation. “For patients who had these surgeries, their total costs after surgery were lower than before.”

Diabetes and obesity

Previous studies in the Annual Review of Medicine and the Journal of the American Heart Association have found that around 85% of people with type 2 diabetes are overweight or obese and 30% to 53% of new cases of diabetes each year are caused by obesity.

“It’s very hard to lose enough weight to keep type 2 diabetes away just by changing what you eat or exercising,” Dr. Kawatkar said. “Because of this, treatments like bariatric surgery, which can help people lose weight and manage diabetes, can be very important and helpful.”

Bariatric surgery helps patients control their blood sugar and sometimes even get rid of diabetes.

“It’s not only good for health, but it can also save money in the long run because people will need less medicine and fewer doctor visits,” Dr. Kawatkar said.

Over 6,000 patients in study

The study included data from 6,657 adults who underwent either bariatric surgery within Kaiser Permanente in Southern California or in Washington between 2012 and 2019. In the study, the researchers analyzed health care costs for 3 years before and 5.5 years after the surgeries.

The cost of bariatric surgery — which can range from $16,000 to $28,000 — was not included in the calculation of health care expenditures.

While both a sleeve gastrectomy and a gastric bypass are weight loss surgeries, they differ in how invasive they are as well as recovery time and weight loss. Sleeve gastrectomy removes part of the stomach, while a gastric bypass creates a smaller stomach pouch and reroutes the small intestine. Researchers found that both gastric bypass and sleeve gastrectomy led to similar reductions in health care expenses.

Cost savings from surgery

The study showed that both surgeries have similar cost drops, with only a small difference in the first 6 months after surgery. In that first 6 months, patients who had gastric bypass had higher health care costs compared to those who had sleeve gastrectomy.

Overall, there were no significant differences in long-term health care costs between the 2 types of surgery, even though previous research suggested that gastric bypass might lead to greater weight loss and higher reoperation rates. These results indicate that both surgeries are equally effective in reducing long-term health care costs for patients with type 2 diabetes, Dr. Kawatkar said.

Health care spending dropped

Before surgery, those who had gastric bypass incurred health care costs of about $4,039 every 6 months, which dropped to $2,441 after surgery. Similarly, the patients who had sleeve gastrectomy saw their expenses decrease from $3,918 to $2,658 every 6 months.

The reduction in total health care expenses was mainly due to a decrease in medication costs. Medication spending dropped from around $2,250 every 6 months before surgery to about $1,000 after surgery for both groups.

Both types of surgery also led to a decline in outpatient expenses, from a peak of about $1,900 in the 6 months before surgery to around $800 per 6 months in the 2 years after surgery, and about $600 per 6 months in the 3 to 5.5 years after surgery. Inpatient expenses varied widely before and after surgery for both groups but generally increased after surgery. For sleeve gastrectomy, inpatient costs ranged from $236 to $1,037 before surgery and increased to $705 to $1,281 after surgery. For gastric bypass, inpatient costs ranged from $227 to $827 before surgery and increased to $693 to $1,273 after surgery.

Dr. Kawatkar said, “Future research should look at subgroups of people with type 2 diabetes who might get even more health and financial benefits from bariatric surgery. Also, longer studies are needed to see if these results last more than 5 years.”

Weight loss medications

The research was conducted prior to the rise of new prescription weight loss drugs: GLP-1 receptor agonists (GLP-1RAs) and sodium-glucose co-transporter-2 inhibitors (SGLT2is). Both are antidiabetic medications that help lower blood sugar levels but also are being used to help people lose weight.

Dr. Kawatkar said the expanding use of these antidiabetic medications for weight loss may have some impact on type 2 diabetes and costs, but research is needed to compare long-term cost and effectiveness of the medications to bariatric surgery.

“GLP1RAs and SGLT2is also produce substantial weight loss and may have similar benefits and downstream cost savings,” he said. “However, in the current environment, as the cost of diabetes medicine goes up because more people are using GLP-1RAs and SGLT2is, bariatric surgery could be a more cost-effective option. More research is needed to confirm this since the cost of the medications are evolving and likely to come down as competition and generic options increase.”

In addition to Dr. Kawatkar, researchers on this study include lead author, Matthew L. Maciejewski, PhD, a professor at Duke University and scientist at the Durham VA Medical Center;  Lindsay Zepel, MS, Valerie A. Smith, DrPH, Caroline Sloan, MD, MPH, Amy G. Clark, PhD, and Ryan M. Kane, MD, MPH, Duke University;  David E. Arterburn, MD, MPH, and Mary K. Theis, MA, MS, Kaiser Permanente Washington Health Research Institute; Aileen Baecker, PhD, and Karen J. Coleman, PhD, Department of Research & Evaluation; Christopher R. Daigle, MD, Washington Permanente Medical Group.

This research was funded in part by the National Institute of Diabetes and Digestive and Kidney Diseases.