Gastric Sleeve vs Gastric Bypass: Weight Loss, Risks and Reflux

Both operations work well. Gastric bypass usually leads to somewhat more weight loss and tends to improve acid reflux, while the gastric sleeve is a simpler operation with fewer early complications but can cause or worsen reflux. In a large U.S. study, people lost an average of 25.5% of their body weight five years after bypass versus 18.8% after sleeve (Arterburn et al., 2018). Two randomized trials found a smaller gap over 10 years.

How each operation works

According to the American Society for Metabolic and Bariatric Surgery (ASMBS):

• Sleeve gastrectomy removes about 80% of the stomach. What's left is a banana-shaped tube. It also removes the part of the stomach that makes most of the "hunger hormone," which reduces hunger.
• Roux-en-Y gastric bypass creates an egg-sized stomach pouch and connects it to the small intestine, so food skips most of the stomach and the first part of the intestine. Bypass has been performed for more than 50 years.

Sleeve vs bypass at a glance

Sources: ASMBS, Arterburn et al..

Weight loss: what the best studies show

Large U.S. cohort

The PCORnet study followed tens of thousands of U.S. patients. At one year, average total weight loss was 31.2% after bypass and 25.2% after sleeve. At five years it was 25.5% and 18.8% (Arterburn et al.). This is real-world data, but patients were not randomly assigned, so people who chose bypass may differ from those who chose sleeve.

Randomized trials

Two trials randomly assigned patients to one operation or the other, which gives a fairer comparison:

• SLEEVEPASS (Finland, 240 patients). At 5 years, excess weight loss was 49% after sleeve and 57% after bypass (Salminen et al., 2018). At 10 years, median excess weight loss was 43.5% and 50.7%. The authors concluded both gave good, lasting weight loss, though bypass did better (Salminen et al., 2022).
• SM-BOSS (Switzerland, 217 patients). At 5 years the difference in excess BMI loss was not statistically significant (Peterli et al., 2018). After 10 years or more, total weight loss was 25.5% after sleeve and 27.7% after bypass, also not significantly different (Kraljevic et al., 2025).

The takeaway: bypass tends to win on weight loss, but the gap in randomized trials is modest. Individual results vary widely in both groups.

Diabetes, blood pressure and other conditions

Both operations improve obesity-related conditions. In SLEEVEPASS at 5 years, type 2 diabetes went into full or partial remission in 37% after sleeve and 45% after bypass, a difference that was not significant. High blood pressure did better after bypass: 51% versus 29% (Salminen et al.). At 10 years, hypertension remission was still better after bypass (24% vs 8%), while differences for diabetes, cholesterol and sleep apnea were not significant (Salminen et al.). ASMBS notes that bypass's hormonal effects often improve diabetes even before much weight is lost (ASMBS).

Reflux: the biggest difference

Heartburn is where the two operations differ most.

• In SM-BOSS, reflux went away more often after bypass (60.4%) than after sleeve (25.0%), and got worse more often after sleeve (31.8% vs 6.3%) (Peterli et al.).
• At 10 years in SLEEVEPASS, esophagitis (inflamed esophagus) was found in 31% after sleeve versus 7% after bypass (Salminen et al.).
• In SM-BOSS, 29.9% of sleeve patients needed conversion to another operation, mostly for reflux or not enough weight loss, versus 5.5% of bypass patients (Kraljevic et al.).

Studies disagree on Barrett's esophagus, a change in the esophagus lining that raises cancer risk. SLEEVEPASS found it in 4% after both operations at 10 years (Salminen et al.). A review of endoscopy studies after sleeve found a pooled rate of 11.6% and suggested screening even without symptoms (Qumseya et al., 2021). If you already have bad reflux, ask your surgeon whether bypass is a better fit.

Safety and long-term risks

In the U.S. cohort, major adverse events within 30 days happened in 2.6% of sleeve patients and 5.0% of bypass patients (Arterburn et al.). Over 10 years, reoperation rates in SLEEVEPASS were similar: 15.7% for sleeve and 18.5% for bypass (Salminen et al.).

ASMBS lists bypass-specific risks: more vitamin and mineral deficiencies, small bowel obstruction, ulcers (especially with tobacco or NSAID painkillers such as ibuprofen), and "dumping syndrome," feeling sick after eating sweets. Bypass patients must avoid tobacco and NSAIDs (ASMBS). After bypass, people need vitamins and minerals for life, including calcium and vitamin D (MedlinePlus).

Daily life after each operation

• Pace of weight loss. MedlinePlus notes that weight usually comes off more slowly after a sleeve than after bypass, and that people keep losing for up to 2 to 3 years (MedlinePlus).
• Alcohol. After bypass, alcohol is absorbed much faster and tolerance drops (MedlinePlus).
• Sweets. Bypass can cause dumping syndrome, so sugary foods may make you feel sick (ASMBS).
• Supplements and checkups. In the SLEEVEPASS trial, patients in both groups were tracked for vitamin use. At 10 years, deficiencies were rare and similar after both operations, except iron deficiency, which was more common after bypass. Sleeve patients were less likely to keep taking their supplements (71% vs 89%) (Saarinen et al., 2025).

Sleeve and bypass are not the only choices. ASMBS also describes the adjustable gastric band, now used less often because of weaker long-term results, and the duodenal switch and SADI-S, which are more complex operations with greater effects on absorption (ASMBS).

Who each operation may suit

Only your surgeon can recommend an operation after reviewing your health. Based on the evidence above, here are common factors:

• Sleeve may suit people who want a simpler operation with fewer early complications and no intestinal rerouting, and who don't have significant reflux. ASMBS notes it can be done in some higher-risk patients (ASMBS).
• Bypass may suit people with significant reflux, those who want the most weight loss, and some with type 2 diabetes or high blood pressure, provided they can commit to lifelong supplements and avoiding NSAIDs and tobacco.

If you are having bariatric surgery abroad

Many Americans travel to Mexico for bariatric surgery. The ASMBS recommends choosing a JCI-accredited hospital or, preferably, a bariatric center of excellence, checking the surgeon's board certification, and setting up follow-up with a local bariatric program before surgery. It also stresses bringing all records home. That matters more for bypass, which needs closer lifelong nutrition monitoring.

The CDC advises not flying for 10 days after abdominal surgery (CDC). Plan your stay accordingly, and talk to your surgeon about blood-clot prevention for the trip home.

Compare programs for the gastric sleeve in Mexico and gastric bypass in Mexico, read Is a gastric sleeve in Mexico safe?, see our guide to recovery houses in Tijuana, and check what insurance covers abroad.

The bottom line

Gastric bypass offers somewhat more weight loss and better reflux control, at the cost of a more complex operation and more nutritional risks. The sleeve is simpler and safer early on, but reflux is a real long-term concern. Both work best with lifelong follow-up.