One-Anastomosis Gastric Bypass (OAGB/MGB)

At a Glance

• What it is: A long, narrow stomach pouch joined to a loop of small intestine with a single connection (also called mini gastric bypass)
• Who it is for: Recommended by the 2022 ASMBS/IFSO guidelines for adults with a BMI of 35 or higher, and considered at a BMI of 30–34.9 with metabolic disease (27.5 or higher for people of Asian descent) (Eisenberg et al., Surgery for Obesity and Related Diseases, 2022)
• Results: Weight loss comparable to Roux-en-Y bypass in a randomized trial (see Landmark Evidence below)
• Main trade-off: Bile reflux and nutritional deficiency in a minority of patients; both are correctable
• Hospital stay and recovery: Usually one night; most return to desk work in one to two weeks

One-anastomosis gastric bypass (OAGB), originally called the mini gastric bypass (MGB), was first described by Rutledge and later refined by Carbajo and Caballero. It is now the third most commonly performed metabolic and bariatric operation in the world. Both the American Society for Metabolic and Bariatric Surgery (ASMBS) and the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) formally endorse it as a primary bariatric procedure (Mitra et al., Obesity Surgery, 2026).

The surgeon creates a long, narrow stomach pouch and joins it to a loop of small intestine with a single connection (anastomosis). Food then bypasses the lower stomach, the duodenum, and the first portion of the small intestine. A traditional Roux-en-Y gastric bypass needs two connections. Removing one shortens the operation and avoids some RYGB-specific complications (Liagre et al., Surgery for Obesity and Related Diseases, 2022).

The evidence base is strong and growing:

• YOMEGA, a multicenter randomized trial in France, found OAGB non-inferior to RYGB for weight loss at both 2 and 5 years, with similar diabetes remission (Robert et al., The Lancet, 2019; Robert et al., The Lancet Diabetes & Endocrinology, 2024)

• In a 10-year comparison of 940 patients, OAGB had half the early complication rate of RYGB (8.1% vs 17.2%) and greater weight loss at 10 years (Liagre et al., Surgery for Obesity and Related Diseases, 2022)

• In U.S. accredited-center data on more than 7,800 matched patients, OAGB carried a 27% lower 30-day complication rate than RYGB (Arshad et al., Surgery for Obesity and Related Diseases, 2024)

OAGB is not for everyone. It causes more reflux than Roux-en-Y bypass, and it can allow bile to flow back into the stomach pouch. Choosing the right patient, and choosing the right length of bypassed intestine, matters more with OAGB than with almost any other bariatric operation. See Gastric Bypass (RYGB) and Sleeve Gastrectomy to compare.

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To compare OAGB with the other operations available in our practice, visit Bariatric & Weight-Loss Surgery in Miami, FL.

OAGB works through three complementary mechanisms:

• Restriction. The long, narrow pouch holds a small volume, so you feel full on much smaller portions.

• Hormonal and metabolic change. Bypassing the duodenum and upper intestine changes gut hormone secretion, bile acid metabolism, and the gut microbiome. These changes drive improvements in blood sugar, cholesterol, and blood pressure that often begin before significant weight loss (De Luca et al., Obesity Surgery, 2026). In a randomized trial, OAGB produced a larger rise in active GLP-1 and post-meal insulin than RYGB, along with better glucose regulation at 12 months (Delko et al., Surgical Endoscopy, 2024).

• Controlled malabsorption. The bypassed segment, called the biliopancreatic limb, is usually 150–200 cm long. Food and digestive juices meet only after that point, which reduces calorie and fat absorption. This is also why limb length is the key safety lever in OAGB. In YOMEGA, a fixed 200 cm limb produced more diarrhea, fatty stools, and nutritional complications than RYGB (Robert et al., The Lancet, 2019).

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• Weight loss equal to or better than Roux-en-Y bypass:
  • A mean 33.2% total weight loss at 5 years across pooled primary-OAGB studies (Sanchez-Cordero et al., Surgery for Obesity and Related Diseases, 2026)
  • The greatest 3-year weight loss (30.9%) among OAGB, RYGB, and sleeve in a national cohort of 6,234 patients (Vinograd et al., Surgery, 2026)
• Strong metabolic remission at 5 years:
  • 77.4% for type 2 diabetes
  • 58.0% for hypertension
  • 71.9% for high cholesterol
  • 86.6% for sleep apnea

(Sanchez-Cordero et al., Surgery for Obesity and Related Diseases, 2026)

• A shorter, simpler operation. Average operating time was 99 vs 126 minutes for RYGB, and the average hospital stay was 1.4 vs 1.6 days (Cornejo et al., Surgical Endoscopy, 2024).
• Fewer early complications than RYGB. In U.S. registry data on primary bypass patients, OAGB had:
  • Overall complications of 1.9% vs 4.5%
  • Readmissions of 2.4% vs 4.9% (Cornejo et al., Surgical Endoscopy, 2024)
  • Bowel obstruction of 0.1% vs 1.0% (Arshad et al., Surgery for Obesity and Related Diseases, 2024)

• Fewer long-term RYGB-type problems. Over 10 years, RYGB had more internal hernias, anastomotic ulcers, and low blood sugar (hypoglycemia), and reoperation for weight regain was more frequent after RYGB (Liagre et al., Surgery for Obesity and Related Diseases, 2022).

• Better quality of life. About 89% of patients report improved quality of life beyond 5 years (Mitra et al., Obesity Surgery, 2026).

• Easier to revise or reverse than many malabsorptive operations if problems develop (Vosburg et al., Surgery for Obesity and Related Diseases, 2026).

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• Adults with a BMI of 35 or higher, or 30 or higher with metabolic disease such as poorly controlled type 2 diabetes. These are the thresholds in the 2022 ASMBS/IFSO guidelines (Eisenberg et al., Obesity Surgery, 2023).

• Patients with type 2 diabetes who want the strongest metabolic effect from a single-connection operation (Delko et al., Surgical Endoscopy, 2024).

• Patients with higher BMIs. In patients with a BMI of 60 or higher, OAGB produced greater weight loss at 18 and 24 months than RYGB (Mechanick et al., AACE/TOS/ASMBS/OMA/ASA Guidelines, 2019).

• Patients with no significant reflux, no Barrett's esophagus, and no large hiatal hernia, confirmed by upper endoscopy and, when indicated, esophageal function testing. Every randomized trial of OAGB excluded patients with severe GERD or Barrett's esophagus (Robert et al., The Lancet, 2019).

• Non-smokers, or patients willing to quit at least 6 weeks before surgery and stay smoke-free for life. More than half of surveyed international experts do not favor OAGB in active smokers (Kermansaravi et al., Obesity Surgery, 2024).

• Patients committed to lifelong vitamins, lab work, and periodic endoscopy (De Luca et al., Obesity Surgery, 2021).

Who is usually better served by a different operation:

• Significant GERD, erosive esophagitis, Barrett's esophagus, or a large hiatal hernia. In an international expert consensus, 84.6% chose RYGB over OAGB for patients with severe GERD or a large hiatal hernia (Bhasker et al., Obesity Surgery, 2024). See Gastric Bypass (Roux-en-Y) for GERD and Gastric Bypass (RYGB).

• Chronic need for NSAIDs or steroids, or inability to stop smoking. These sharply raise marginal ulcer risk with any bypass. Sleeve Gastrectomy may be safer.

• Patients seeking maximal weight loss, especially at very high BMI. See SADI-S, Duodenal Switch, or Magnetic Duodeno-Ileostomy with Sleeve Gastrectomy (MagDI).

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OAGB is performed laparoscopically or robotically under general anesthesia through 5–6 small incisions:

1. Pouch creation. Stapling starts on the lesser curve of the stomach at about the level of the crow's foot and runs up to the angle of His over a 34–36 French calibration tube (bougie). This creates a long, narrow pouch about 15 cm long (Al-Hasani et al., Scientific Reports, 2025; Kermansaravi et al., Scientific Reports, 2022).
2. Measuring the intestine. The small bowel is measured from the ligament of Treitz, and the biliopancreatic limb is set at 150–200 cm. Some surgeons adjust the length to the patient's BMI (Slagter et al., Obesity Surgery, 2021) or to measured total small bowel length (Abu-Abeid et al., Obesity Surgery, 2025).
3. The single anastomosis. The intestinal loop is brought up in front of the colon. It is joined side-to-side to the pouch with a linear stapler, and the opening is closed with sutures (Al-Hasani et al., Scientific Reports, 2025).
4. Leak testing. An air or methylene blue leak test checks the staple lines and the connection (Kermansaravi et al., Scientific Reports, 2022).
5. Hiatal assessment. The diaphragm opening is inspected, and any hiatal hernia is addressed.

In Dr. de la Cruz-Muñoz's hands, the operation typically takes 45–60 minutes.

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Early (first 30 days): In U.S. registry data, overall complications were 1.9%, with leak and bleeding rates similar to RYGB (Cornejo et al., Surgical Endoscopy, 2024). Compared with sleeve gastrectomy, OAGB had more reoperations (1.2% vs 0.5%) and more emergency visits (10.6% vs 7.4%) (Sebastian et al., Surgery for Obesity and Related Diseases, 2026).

Long-term (beyond 5 years, pooled):

• Bile reflux in about 4% of patients (Mitra et al., Obesity Surgery, 2026). Rates are higher when patients are formally tested. One cohort found 20% on pH-impedance monitoring (Delcarro et al., Surgery for Obesity and Related Diseases, 2026).

• Marginal ulcers in about 2–3% of patients. About 90% heal with medication. Smoking, NSAIDs, and H. pylori are the main risk factors (Shahabi Shahmiri et al., Obesity Surgery, 2025).

• Iron-deficiency anemia in about 4% and clinically significant malnutrition in about 1% (Mitra et al., Obesity Surgery, 2026).

• Conversion to Roux-en-Y gastric bypass in about 3%, mostly for bile reflux (Mitra et al., Obesity Surgery, 2026). In YOMEGA, 8% of OAGB patients were converted by 5 years (Robert et al., The Lancet Diabetes & Endocrinology, 2024).

• More diarrhea, abdominal pain, ulcers, and anal fissures than after sleeve (Vinograd et al., Surgery, 2026).

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• Hospital stay: most patients go home within 1–2 days. The average stay is 1.3–1.4 days (Cornejo et al., Surgical Endoscopy, 2024; Sebastian et al., Surgery for Obesity and Related Diseases, 2026). Under enhanced recovery protocols, many are discharged on day 1 once they tolerate clear liquids (Kermansaravi et al., Scientific Reports, 2022).

• Walking: starts the day of surgery.

• Diet: advances in stages from clear liquids to full liquids, purées, soft foods, and regular textures over about 6–8 weeks.

• Return to work: most patients go back to desk work in 1–3 weeks.

• Medications: a proton pump inhibitor for at least 6 months after OAGB is supported by international expert consensus (Bhasker et al., Obesity Surgery, 2024). Ursodiol for about 6 months is commonly used to prevent gallstones during rapid weight loss (Bhasker et al., Obesity Surgery, 2024).

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• Weight loss: reported excess weight loss is 81.8% at 5 years and 62.3% at 8 years, and about 86% of patients report improved quality of life at a mean of 92 months (Shahmiri et al., Obesity Surgery, 2025).

• Five-year trial results: in YOMEGA, excess BMI loss was 75.6% with OAGB vs 71.4% with RYGB (Robert et al., The Lancet Diabetes & Endocrinology, 2024).

• Ten-year results: at 10 years, OAGB patients had lower weight and BMI than RYGB patients (Liagre et al., Surgery for Obesity and Related Diseases, 2022).

• What remains uncertain: independent reviews note that long-term evidence is still heterogeneous. In particular, the long-term effects of bile reflux and the full picture of nutrition are not yet fully understood (Sanchez-Cordero et al., Surgery for Obesity and Related Diseases, 2026).

• Endoscopic surveillance: lifelong follow-up includes periodic endoscopy. IFSO-aligned experts suggest endoscopy at 1 year and then every 2–3 years (Kermansaravi et al., Obesity Surgery, 2024).

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Landmark Evidence

• YOMEGA randomized trial: OAGB was non-inferior to Roux-en-Y bypass for weight loss at two years, but nutritional adverse events were more common with a 200 cm bypassed limb (Robert et al., The Lancet, 2019).
• IFSO position statement: IFSO recognizes OAGB as a mainstream bariatric operation and reviews evidence that a 150 cm limb gives weight loss similar to 200 cm (De Luca et al., Obesity Surgery, 2021).
• When conversion is needed: in a multicenter series, bile reflux was the leading reason for converting OAGB to Roux-en-Y bypass, and it resolved in all patients followed for two years (Antonopulos et al., Obesity Surgery, 2022).
• Survival: Across 17 studies and more than 174,000 people, metabolic and bariatric surgery was associated with a 49% lower risk of death and a median of 6.1 additional years of life compared with non-surgical care. The benefit was greatest in people with type 2 diabetes (Syn et al., The Lancet, 2021).

How It Compares

• Versus Roux-en-Y bypass: one connection instead of two and similar weight loss, but more bile reflux and nutritional risk.
• Versus sleeve: more weight loss and diabetes effect, with intestinal bypass trade-offs.
• Versus SADI-S: both use a single connection. SADI-S preserves the pylorus and bypasses at the duodenum.

More in Bariatric Surgery Procedures

Related procedures: SADI-S, Duodenal Switch, Magnetic Duodeno-Ileal Bypass with Sleeve, Adjustable Gastric Band Surgery, Medical Weight Loss Program, Robotic Surgery. Related primary operations: Gastric Bypass. For an overview of all options, see Bariatric Surgery.

Conditions treated: Obesity, Type 2 Diabetes, Sleep Apnea, Metabolic Dysfunction–Associated Steatohepatitis, Metabolic Syndrome, High Blood Pressure.

OAGB rewards precision. Its results depend on factors that change from one patient to the next:

• The length of bypassed intestine

• The construction of the pouch

• A thorough reflux evaluation before surgery

OAGB is endorsed by both the ASMBS and IFSO and is the third most common bariatric operation worldwide. It is still offered at relatively few U.S. centers: it accounted for fewer than 1% of primary bariatric operations in a recent national registry analysis (Sebastian et al., Surgery for Obesity and Related Diseases, 2026).

Dr. Nestor de la Cruz-Muñoz, MD, FACS, DABOM, is a board-certified surgeon and a diplomate of the American Board of Obesity Medicine, so he treats obesity both medically and surgically. He served for 10 years as a bariatric surgery fellowship program director, training surgeons in bypass, single-anastomosis, and revisional operations. His practice is also a regional referral center for reflux and hiatal hernia surgery. That matters here because whether you have reflux is the single most important factor in choosing OAGB over Roux-en-Y bypass.

Every OAGB candidate receives:

• Upper endoscopy

• Reflux and esophageal function testing when indicated

• A nutritional baseline

• H. pylori screening

• A side-by-side review of OAGB, Gastric Bypass (RYGB), Sleeve Gastrectomy, and SADI-S

If bile reflux or ulcers develop later, the same team performs OAGB to Gastric Bypass Conversion.

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Dr. de la Cruz-Muñoz has been performing bariatric surgery for over 25 years and has completed more than 9,000 bariatric operations — a volume few surgeons reach.

Authored by Nestor de la Cruz-Muñoz, MD, FACS, DABOM. Last updated November 2026.

• 6 months: about 23%

• 12 months: about 26% (Heinonen et al., Obesity, 2023)

• 3 years: about 31% (Vinograd et al., Surgery, 2026)

• 5 years: about 33% on average across pooled studies (Sanchez-Cordero et al., Surgery for Obesity and Related Diseases, 2026)

Individual results vary. Results depend on starting BMI, limb length, nutrition, activity, and follow-up.

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• Type 2 diabetes:
  • Remission in about 77% at 5 years (Sanchez-Cordero et al., Surgery for Obesity and Related Diseases, 2026)
  • Remission similar to RYGB in randomized trials (Robert et al., The Lancet Diabetes & Endocrinology, 2024)
  • Better glucose regulation and greater GLP-1 response than RYGB at 12 months (Delko et al., Surgical Endoscopy, 2024)

• Hypertension: remission in about 58%. In one randomized trial, blood pressure medication was reduced more after RYGB (Heinonen et al., Obesity, 2023).

• Cholesterol: remission of dyslipidemia in about 72% (Sanchez-Cordero et al., Surgery for Obesity and Related Diseases, 2026).

• Sleep apnea: remission in about 87% (Sanchez-Cordero et al., Surgery for Obesity and Related Diseases, 2026).

• Insulin sensitivity and inflammation: improve similarly to RYGB (Heinonen et al., Obesity, 2023).

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• Structured follow-up at 1, 3, 6, and 12 months, then every year for life

• Protein-first eating, with a daily protein target set by your dietitian (commonly 60–80 grams)

• Resistance training at least 2 days a week to preserve muscle and metabolic rate

• Body composition tracking rather than relying on scale weight alone

• Early use of anti-obesity medication if weight plateaus or regain begins

• Surgical options if needed. In the 10-year comparison, reoperation for weight regain was less frequent after OAGB than after RYGB (Liagre et al., Surgery for Obesity and Related Diseases, 2022).

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Reflux is the most important trade-off with OAGB.

• Trial data: in YOMEGA, clinical GERD at 5 years occurred in 41% of OAGB patients vs 18% of RYGB patients (Robert et al., The Lancet Diabetes & Endocrinology, 2024).
• Pooled data: across 87 studies and 27,775 patients:
  • New-onset reflux in 6%
  • Esophagitis in 15%
  • Barrett's esophagus in 1%
  New-onset reflux was higher than after RYGB and similar to sleeve (Esparham et al., Obesity Surgery, 2023).

• Compared with sleeve over the long term: in a prospective study, reflux symptoms were unchanged after OAGB but rose sharply after sleeve. Barrett's esophagus was found only after sleeve (16.8%) (Genco et al., British Journal of Surgery, 2021).
• Bile in the esophagus is uncommon. In a 5-year endoscopic study of 1,147 patients:
  • Bile was seen in the pouch in 6.8% and in the esophagus in none
  • No Barrett's esophagus or dysplasia was found (Pizza et al., Obesity Surgery, 2026)

• Cancer risk: IFSO reports no increase in esophageal or gastric cancer to date. It still recommends regular endoscopy because cancers take a long time to develop (De Luca et al., Obesity Surgery, 2021).

• Testing before surgery predicts risk. In one cohort, every patient who developed GERD after OAGB had a weak lower esophageal sphincter (under 16 mmHg) on preoperative manometry. No patient with normal sphincter pressure developed GERD or esophagitis (Delcarro et al., Surgery for Obesity and Related Diseases, 2026).

Patients with established reflux are typically directed to Gastric Bypass (Roux-en-Y) for GERD. See also GERD / Acid Reflux and Barrett's Esophagus.

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• OAGB to Gastric Bypass Conversion. This is the standard fix for bile reflux, refractory marginal ulcer, or severe GERD. All patients converted for bile reflux had complete symptom resolution (Delcarro et al., Surgery for Obesity and Related Diseases, 2026).

• Limb shortening or partial reversal. This is used for chronic diarrhea or protein malnutrition. These revisions carry real risk, with morbidity of 31–41% (Vosburg et al., Surgery for Obesity and Related Diseases, 2026).

• Perforated or bleeding marginal ulcers. These are treated as they are after RYGB. See Surgical Repair of Perforated Ulcer and Surgical Management of Bleeding Ulcer.

• Revision for weight regain. This is individualized. See Revision Bariatric Surgery.

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OAGB produces substantial weight loss, but the real goal is fat loss with muscle preservation. The operation increases GLP-1, improves insulin sensitivity, and reduces hunger — but patients must protect lean mass through:

• High protein intake (80–120 g/day) depending on sex and baseline muscle mass
• Early resistance training beginning at Week 4–6
• Adequate hydration (64–80 oz/day) to support metabolic recovery
• Daily movement to maintain mitochondrial efficiency
• Avoiding rapid-carb eating which accelerates lean mass loss

Patients who follow a structured protein-first plan maintain 90–95% of their lean mass, which directly predicts long-term weight stability.

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Most insurers require documentation of BMI criteria, comorbidities, supervised weight-loss attempts, and medical clearance. Our team handles verification and authorization.

OAGB candidates must complete:

• Full metabolic evaluation (A1c, fasting insulin, C-peptide, lipid panel, liver function, vitamin levels)
• Upper endoscopy if history of reflux, ulcers, or prior sleeve
• Nutritional clearance with education on protein targets, vitamin protocol, and staged diet
• Psychological readiness assessment
• Cardiac clearance for patients with risk factors
• Pre-op liver-shrink diet (2 weeks) to reduce liver size and improve surgical exposure
• Cessation of nicotine for 6 weeks minimum
• GLP-1 management plan if currently using semaglutide/tirzepatide

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OAGB requires lifelong nutritional monitoring due to mild–moderate malabsorption.

Daily Requirements

• Multivitamin with iron
• Calcium citrate 1200–1500 mg/day
• Vitamin D3 3000 IU/day
• Vitamin B12 1000 mcg/day (oral or sublingual)
• Thiamine 100 mg/day during rapid weight loss
• Protein 80–120 g/day
• Fluids 64–80 oz/day

Diet Progression

• Weeks 1–2: liquids
• Weeks 3–4: purées
• Weeks 5–6: soft foods
• Week 7+: structured protein-first meals

Monitoring

• Labs at 3, 6, 12 months, then annually
• Watch for bile reflux symptoms (rare but possible)
• Avoid NSAIDs and nicotine

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A 7-level progression (see our 7-level exercise guide):

1. Level 1: Walking 5–10 minutes/day
2. Level 2: Walking 20–30 minutes/day
3. Level 3: Light resistance bands
4. Level 4: Bodyweight training (squats, wall pushups)
5. Level 5: Gym machines (leg press, lat pulldown)
6. Level 6: Free weights and progressive overload
7. Level 7: Full strength training + metabolic conditioning

Goal: 3–4 resistance sessions/week + 6–8k steps/day.

For patients traveling from abroad:

• Virtual pre-operative consults
• Remote nutritional and psychological clearance
• Travel-safe scheduling (plan for approximately one week in Miami)
• International pharmacy coordination for vitamins and medications
• Telehealth follow-up at 2 weeks, 6 weeks, 3 months, 6 months, 12 months
• Emergency return plan if complications arise
• Multilingual support (English/Spanish)

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