The main finding
In one sentence: In a randomized trial of 150 adults with obesity and poorly controlled type 2 diabetes, 42% of those who had gastric bypass and 37% of those who had sleeve gastrectomy reached an HbA1c of 6.0% or less at 12 months, compared with 12% of those on intensive medical therapy alone.
Group averages, not an individual prediction. A trial result describes what happened to a defined group over a defined time.
On this page
Why this study matters
Before STAMPEDE, studies that watched people over time had noticed that type 2 diabetes often improved after bariatric surgery (an operation on the stomach or gut to help with weight loss). But watching is not the same as testing. STAMPEDE was a randomized trial, which is the fairest way to compare treatments. It asked whether adding surgery to intensive medical care gets more people to a tight blood-sugar target than medical care alone. Canadian readers living with both obesity and type 2 diabetes may see this trial cited by clinicians and guidelines.
Who was in the study
The trial enrolled 150 adults with obesity and uncontrolled type 2 diabetes. Their average age was 49 years (standard deviation 8), and 66% were women. Their average glycated hemoglobin, or HbA1c, was 9.2% (standard deviation 1.5). HbA1c is a blood test that shows average blood sugar over about three months, and the trial described these participants as having uncontrolled diabetes. The trial ran at a single centre, and 93% of participants completed 12 months of follow-up.
What the researchers did
People were randomized, meaning a computer assigned them by chance, to one of three groups: intensive medical therapy alone, medical therapy plus Roux-en-Y gastric bypass, or medical therapy plus sleeve gastrectomy. Gastric bypass reroutes food past most of the stomach. Sleeve gastrectomy removes a large part of the stomach. The trial was nonblinded (also called open-label), meaning everyone knew which treatment they got. Blinding is not possible with surgery.
All three groups received intensive medical therapy. The published summary does not describe its details. The main outcome was the share of people whose HbA1c was 6.0% or less at 12 months.
What they found
The main result favoured surgery. An HbA1c of 6.0% or less was reached by 12% of the medical therapy group (5 of 41), 42% of the gastric bypass group (21 of 50; P=0.002 compared with medical therapy), and 37% of the sleeve gastrectomy group (18 of 49; P=0.008) (R32-C105). A P value below 0.05 is usually treated as statistically significant, meaning the difference is unlikely to be due to chance. The summary we reviewed does not report confidence intervals for these comparisons.
| Result at 12 months | Medical therapy alone | Gastric bypass | Sleeve gastrectomy |
|---|---|---|---|
| HbA1c 6.0% or less | 12% (5 of 41) | 42% (21 of 50) | 37% (18 of 49) |
| Average HbA1c | 7.5% | 6.4% | 6.6% |
| Average weight change | loss of 5.4 kg | loss of 29.4 kg | loss of 25.1 kg |
Blood sugar improved in all three groups. Weight loss was greater in both surgical groups than with medical therapy (P less than 0.001 for both comparisons). The use of medicines for blood sugar, cholesterol, and blood pressure went down after both surgeries but went up in the medical therapy group. A measure of insulin resistance (HOMA-IR) also improved after surgery.
Side effects and people who stopped
Four patients needed a second operation. The summary reports no deaths and no life-threatening complications. The extracted data show that 7 people in the medical therapy group and 1 in the sleeve gastrectomy group withdrew, and 2 more medical therapy participants missed the 9-month and 12-month visits. In total, 140 people completed all analyses. The summary does not report side effects in detail.
What this study does not tell you
- The trial was small (150 people) and ran at one centre, so the results may not apply everywhere.
- Because it was unblinded, people's expectations could have influenced some outcomes.
- The medical therapy used in this trial predates the newer diabetes and weight-management medicines available today. STAMPEDE does not compare surgery with those medicines.
- One year is a short time. The three-year and five-year STAMPEDE reports follow the same people and are the place to look for longer results.
- The summary does not describe how missing data were handled beyond the number of completers.
- The trial was funded in part by a maker of surgical devices, which is worth knowing when reading the results.
What it means in Canada
STAMPEDE is often cited in Canadian discussions about treating type 2 diabetes in people living with obesity. It does not tell you whether surgery is right for you, and it does not compare surgery with the medicines used today. For information on medicines, see semaglutide in Canada and tirzepatide in Canada. For questions about what provincial plans pay for, see public drug coverage by province.
Common questions
What did the STAMPEDE trial find at 12 months?
An HbA1c of 6.0% or less was reached by 42% after gastric bypass, 37% after sleeve gastrectomy, and 12% with intensive medical therapy alone.
How much weight did people lose in the STAMPEDE trial after one year?
Average weight change was a loss of 29.4 kg after gastric bypass, 25.1 kg after sleeve gastrectomy, and 5.4 kg with medical therapy alone.
Were there deaths or serious complications in the first year of STAMPEDE?
The summary reports no deaths and no life-threatening complications. Four patients needed a second operation.
Related reading
Other studies in this library that bear on the same question.
STAMPEDE at three years: surgery versus medical therapy
STAMPEDE at five years: surgery versus medical therapy
Bariatric surgery and death rates: the Swedish Obese Subjects study
STEP 2: semaglutide for weight loss in type 2 diabetes
SURMOUNT-2: tirzepatide for weight loss in type 2 diabetes
Source
Original paper: Philip R Schauer, STAMPEDE primary, The New England journal of medicine, 2012. PubMed: https://pubmed.ncbi.nlm.nih.gov/22449319/. DOI: https://doi.org/10.1056/NEJMoa1200225. Funding: The trial was funded by Ethicon Endo-Surgery, with support from LifeScan, the Cleveland Clinic and the National Institutes of Health. How we summarized it: full text and extracted data.
This page explains a published study. It is not medical advice and does not describe whether a medicine is right for you. Talk to your doctor, nurse practitioner or pharmacist about your own situation. Reviewed and signed by two pharmacists registered in British Columbia, 2026-09-18.
Evidence records behind this page
Each record is a row in the clinical evidence file, taken from the published paper named above. The caution column is the limit the researcher recorded for that number.
This table scrolls sideways.
| Record | What the paper reports | Type | Population | Caution | Source |
|---|---|---|---|---|---|
| R32-C105 | At 12 months in STAMPEDE, the HbA1c target of 6.0% or less was reached by 42% after gastric bypass,37% after sleeve gastrectomy and 12% with intensive medical therapy alone. | direct evidence | Adults with obesity and uncontrolled T2D | Unblinded single centre; small sample; four reoperations and short initial follow-up. Not a comparison with present-day incretin regimens. Extensions 24679060/28199805. | PubMed 22449319 |