Results Summary

What was the research about?

Some adults and youth with severe obesity can’t lose enough weight with diet and exercise to improve their health. Different types of surgery may help people lose weight and improve problems related to obesity like diabetes. But surgery has risks, including needing more surgery to reverse or fix the original surgery.

In this study, the research team compared three types of weight-loss surgery:

  • In Roux-en-Y gastric bypass, or RYGB, a surgeon uses part of the stomach to create a pouch that holds a small amount of food. The surgeon attaches this pouch to the small intestine. With this bypass, the body absorbs fewer calories.
  • In adjustable gastric banding, or AGB, a surgeon places a band around the upper part of the stomach. This band limits how much a person can eat.
  • In sleeve gastrectomy, or SG, a surgeon removes a large part of the stomach, which also limits the amount of food a person can eat.

The research team looked at patients’ health records to see how surgery affected

  • Weight loss in 46,510 adults and in 544 youth ages 12–19
  • Effects on diabetes in 10,019 adults with type 2 diabetes
  • The need for more surgery in 34,714 adults

What were the results?

Weight loss in adults. With all three types of surgery, patients lost weight and then regained some weight over five years. At five years, adult patients who had RYGB lost 26 percent of their total weight compared with before surgery. Patients who had SG lost 19 percent and patients who had AGB lost 12 percent.

Diabetes. Diabetes went away at some point in the five years after surgery for 86 percent of patients with diabetes who had RYGB, 84 percent of patients who had SG, and 65 percent of patients who had AGB.

Need for more surgery. Adults who had SG had a 9 percent chance of needing another surgery in five years compared with 12 percent of people who had RYGB and 41 percent who had AGB.

Weight loss in youth. One year after surgery, youth who had RYGB lost an average of 31 percent of their body mass index, or BMI. Youth who had SG lost an average of 28 percent of BMI, and youth who had AGB lost an average of 10 percent.

What did the research team do?

The research team looked at health data for patients who had a BMI of at least 35 and had surgery between 2005 and 2015. Patient data came from 41 health systems around the country that were part of PCORnet®.

Patients, advocacy groups, surgeons, and health insurers helped plan the study.

What were the limits of the study?

Patients and their doctors chose what type of surgery to have. Results may have differed if the research team had assigned patients by chance to the type of surgery. The study didn’t include outpatient surgery centers, which may do more AGB surgeries.

Future research could track patients’ weight regularly.

How can people use the results?

Patients with obesity and their doctors can use these results when considering surgery for weight loss.

How this project fits under PCORI’s Research Priorities
The PCORnet® Study reported in this results summary was conducted using PCORnet®, the National Patient-Centered Clinical Research Network. PCORnet® is intended to improve the nation’s capacity to conduct health research, particularly comparative effectiveness research (CER), efficiently by creating a large, highly representative network for conducting clinical outcomes research. PCORnet® has been developed with funding from the Patient-Centered Outcomes Research Institute® (PCORI®).

Final Research Report

View this project's final research report.


Related PCORI Dissemination and Implementation Project

Journal Citations

Article Highlights: The PCORnet® Bariatric Study, which is using data from PCORnet, The National Patient-Centered Clinical Research Network, to study outcomes among patients who undergo common weight-loss surgeries, has published several papers in prominent medical journals. The most recent clinical findings, published in JAMA Surgery, are on diabetes remission outcomes among patients who underwent gastric bypass and gastric sleeve surgeries. Another article, also published in JAMA Surgery, details the five-year outcomes of patients who underwent either gastric bypass or adjustable banding, finding that gastric bypass patients were significantly more likely than gastric sleeve patients to end up back in the hospital in the years following surgery.

Peer-Review Summary

Peer review of PCORI-funded research helps make sure the report presents complete, balanced, and useful information about the research. It also assesses how the project addressed PCORI’s Methodology Standards. During peer review, experts read a draft report of the research and provide comments about the report. These experts may include a scientist focused on the research topic, a specialist in research methods, a patient or caregiver, and a healthcare professional. These reviewers cannot have conflicts of interest with the study.

The peer reviewers point out where the draft report may need revision. For example, they may suggest ways to improve descriptions of the conduct of the study or to clarify the connection between results and conclusions. Sometimes, awardees revise their draft reports twice or more to address all of the reviewers’ comments. 

Peer reviewers commented and the researchers made changes or provided responses. Those comments and responses included the following:

  • The reviewers asked why the researchers did not perform propensity score analyses on some specific parts of the study, such as safety outcomes, to account for any differences between groups in this observational study. The researchers explained that they found the propensity score adjustments did not change results enough to warrant accepting certain assumptions and checking propensity distributions.  In addition, because the hypotheses in these studies were associative instead of causal, the reviewers felt that the covariate adjustment was sufficient without a propensity score adjustment.
  • The reviewers asked whether the researchers specified subgroup analyses in advance and whether they were driven by hypotheses. The researchers responded that they specified all subgroup analyses in advance but that they considered the analyses exploratory rather than driven by hypotheses.
  • The reviewers asked why in the qualitative study, patient feedback was sought in focus groups rather than in individual interviews. Since obesity and bariatric surgery can be socially sensitive topics, the reviewers noted that having to answer questions in a group setting may have affected responses. The researchers said funding constraints did not allow for individual interviews, particularly since they wanted to maximize sample size and representation of patients from different parts of the country. They acknowledged that using focus groups was a limitation of the study.
  • The reviewers asked why the frequency of obesity-related cancers, including colorectal cancer, was not analyzed as an outcome. The researchers explained that they excluded patients with certain types of cancers, especially gastrointestinal (GI) cancers, because some patients with GI cancer will undergo a procedure for the cancer that is coded the same as bariatric surgery in electronic health records. 

Conflict of Interest Disclosures

Project Information

David Arterburn, MD, MPH
Kaiser Permanente Washington Health Research Institute^
Comparing the Benefits and Harms of Three Types of Weight Loss Surgery -- The PCORnet® Bariatric Study

Key Dates

August 2015
July 2022

Study Registration Information

^Kaiser Permanente acquired Group Health Cooperative in February 2017.


Has Results
Health Conditions Health Conditions These are the broad terms we use to categorize our funded research studies; specific diseases or conditions are included within the appropriate larger category. Note: not all of our funded projects focus on a single disease or condition; some touch on multiple diseases or conditions, research methods, or broader health system interventions. Such projects won’t be listed by a primary disease/condition and so won’t appear if you use this filter tool to find them. View Glossary
Populations Populations PCORI is interested in research that seeks to better understand how different clinical and health system options work for different people. These populations are frequently studied in our portfolio or identified as being of interest by our stakeholders. View Glossary
Intervention Strategy Intervention Strategies PCORI funds comparative clinical effectiveness research (CER) studies that compare two or more options or approaches to health care, or that compare different ways of delivering or receiving care. View Glossary
State State The state where the project originates, or where the primary institution or organization is located. View Glossary
Last updated: April 22, 2024