Results Summary

What was the research about?

Weight loss surgery may help people with severe obesity lose weight and improve their health. Most research on weight loss surgery has focused on its clinical health outcomes, such as weight loss and its effect on diabetes. But patients are also interested in how surgery can improve their quality of life and well-being, such as their ability to do daily activities.

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

  • Gastric bypass, in which 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 gastric bypass, the body takes in fewer calories, and patients feel full after eating less food.
  • Gastric sleeve surgery, in which a surgeon removes a large part of the stomach. This surgery limits the amount of food a person can eat.

The research team looked at patient reports related to quality of life and well-being.

What were the results?

One and two years after surgery, patients who had either gastric bypass or gastric sleeve surgery reported:

  • Fewer problems with daily activities related to obesity
  • Improved quality of life
  • Better physical and mental health

One year after surgery, compared with patients who had gastric bypass, patients who had gastric sleeve surgery reported:

  • More problems with daily activities related to obesity
  • Lower quality of life

Patients having the two types of surgeries did not differ in physical and mental health.

Who was in the study?

The study included 11,146 adults with obesity who were scheduled for or had received weight loss surgery at one of 82 hospitals in the United States. Of these adults, 79 percent were White; 13 percent were non-Hispanic Black; 1 percent were American Indian or Alaska Native, Asian, or another race; and 7 percent were an unknown race. Most patients (79 percent) were between 30 and 59 years old, and 82 percent were women.

What did the research team do?

The research team interviewed 18 groups of patients, family members, and doctors. They asked about which outcomes were most important to patients having either type of surgery. Based on these interviews, the team picked health outcomes to focus on in this study. Before surgery and one and two years later, patients completed surveys about these outcomes. The team compared results for patients who received one of the two types of surgery.

Patients with obesity, surgeons, and health insurers gave input during the study.

What were the limits of the study?

Fewer hospitals than planned took part in the study. Results may have differed if more hospitals took part in the study. 

Future research could look at other outcomes about weight loss surgery that are important to patients and include more hospitals in the study.

How can people use the results?

Patients with obesity and their doctors can use these results when considering treatment options.

Final Research Report

This project's final research report is expected to be available by October 2024.

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 noted that the study focus groups led to the researchers choosing three patient-reported outcomes measures (PROMs) to be used in the comparative clinical trial, but there was little information about these three measures in the final report. The researchers added more information, including the structure and the domains covered, about the chosen measures in the methods section of the report.
  • The reviewers commented on the planned study analyses that were not conducted in the research. They understood that this was largely due to changes in the study design but asked the researchers to explain the changes in analyses more clearly. The researchers acknowledged that they did not carry through changes to the study protocol to make changes to the statistical plan. They did add language to the report explaining that two expected changes in implementation of the PROMs in a large-scale quality improvement program for metabolic and bariatric surgery (MBS) did not occur, reducing the scale of the program and therefore the sample size for analyses. The researchers explained that they changed their analytic plan due to this reduction.
  • The reviewers asked for more information about how the researchers calculated power and effect size for their study. The researchers added an explanation about their sample size calculations needed to assume 90% power in detecting differences on the PROMs. They also added effect size estimates to a table listing the anticipated sample size requirements. They noted, however, that the changes to the improvement program meant that they did not have sufficient power to determine if any of their secondary outcomes were mediators of the main outcomes.
  • The reviewers noted that there was a lack of diversity among the focus group participants, who were all recruited from the same region. Further, the reviewers were concerned that all of the MBS study participants had to be English-speaking. The researchers acknowledged these as limitations, explaining that these limitations were driven by limited resources.
  • The reviewers asked the researchers to explain the difference between their measures of total weight and excess weight. The researchers explained that total weight indicates the amount of weight change between pre-operative and post-operative weights, whereas excess weight refers to the amount of weight participants carry above the goal weight equaling a BMI of 25.
  • The reviewers were confused about the report’s use of Alpha and Beta pilots and their relationship to the focus groups. The researchers explained that participants in the pilots were not the same as participants in the focus groups. Rather, the third round of focus groups focused on the Alpha pilot, which was small, and the fourth round of focus groups focused on the Beta pilot, which was considerably larger.

Conflict of Interest Disclosures

Project Information

Matthew Hutter, MD, MPH
Massachusetts General Hospital
Comparative Effectiveness of Metabolic and Bariatric Surgery using Patient Reported Outcome Measures (PROMs)

Key Dates

September 2015
November 2023

Study Registration Information


Has Results
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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
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Last updated: March 14, 2024