The Bariatric Surgery Encyclopedia

Bariatric surgery is a group of weight loss surgical procedures performed on people with obesity. Common types include gastric bypass (Roux-en-Y), sleeve gastrectomy, adjustable gastric banding (Lap-Band), and biliopancreatic diversion with duodenal switch. These procedures work by restricting the amount of food the stomach can hold, causing malabsorption of nutrients, or a combination of both. Candidates typically have a BMI of 40 or higher, or a BMI of 35 or higher with serious obesity-related health conditions. Learn more in our A–Z encyclopedia.

The most common types of bariatric surgery are: Roux-en-Y Gastric Bypass (divides the stomach into a small upper pouch and reroutes the small intestine), Sleeve Gastrectomy (removes approximately 80% of the stomach), Adjustable Gastric Banding / Lap-Band (places an inflatable band around the upper portion of the stomach), and Biliopancreatic Diversion with Duodenal Switch (removes a large portion of the stomach and bypasses most of the small intestine). Sleeve gastrectomy is currently the most performed bariatric procedure worldwide. Browse all surgical procedure terms →

After bariatric surgery, patients typically need to take lifelong vitamin and mineral supplements including: a high-potency multivitamin with minerals (including zinc, copper, and selenium), Calcium Citrate (1,200–1,500 mg daily in divided doses), Vitamin D3 (3,000 IU daily minimum), Vitamin B12 (sublingual, injections, or oral depending on procedure), Iron (45–60 mg daily, taken separately from calcium), and Folate. Liquid gel cap formulations like Bari Liquid Force are often recommended because they absorb more rapidly in a surgically altered digestive system. See our complete Bariatric Vitamin & Supplement Guide for full dosage details by procedure type.

After bariatric surgery, patients follow a phased diet progression: Phase 1 (Days 1–2) consists of clear liquids only. Phase 2 (Weeks 1–2) includes full liquids like protein shakes, broth, and sugar-free beverages. Phase 3 (Weeks 3–4) introduces pureed foods. Phase 4 (Weeks 5–6) allows soft foods like scrambled eggs, cottage cheese, and canned fish. Phase 5 (Week 7 onward) gradually reintroduces regular foods with an emphasis on lean protein first (60–80g daily minimum), then vegetables, then complex carbohydrates. Patients should eat slowly, chew thoroughly, avoid sugar and carbonation, and stop eating when full. View the complete post-op diet stages guide →

Dumping syndrome is a common condition after gastric bypass surgery where food moves too quickly from the stomach into the small intestine. Early dumping occurs 10–30 minutes after eating and causes nausea, cramping, diarrhea, dizziness, and sweating. Late dumping occurs 1–3 hours after eating and causes weakness, sweating, shakiness, and low blood sugar. It is most commonly triggered by high-sugar or high-fat foods. Managing dumping syndrome involves eating smaller meals, avoiding simple sugars, separating liquids from solids by 30 minutes, and increasing protein and fiber intake. Learn more about bariatric complications →

Expected weight loss varies by procedure. Roux-en-Y Gastric Bypass patients typically lose 60–80% of excess body weight within 12–18 months. Sleeve Gastrectomy patients typically lose 50–70% of excess body weight. Adjustable Gastric Banding patients typically lose 40–50% of excess body weight, often more gradually. Duodenal Switch patients may lose 70–85% of excess body weight. Long-term success depends on adherence to dietary guidelines, regular exercise, vitamin supplementation, and ongoing follow-up with a bariatric care team.