Gastric Sleeve vs Gastric Bypass: How to Choose the Right Weight-Loss Surgery

In a gastric sleeve (sleeve gastrectomy), around 80% of the stomach is removed through small keyhole incisions, leaving a narrow, sleeve-shaped stomach. According to the NHS, the operation usually takes 1 to 3 hours.

The smaller stomach holds less food, so you feel full sooner. Removing part of the stomach also reduces a hormone that drives hunger, which helps many patients eat less without constant cravings. A sleeve is not reversible.

In a gastric bypass, the stomach is divided with staples to create a small pouch at the top. This pouch is then connected to a lower part of the small intestine, so food bypasses most of the stomach and the first section of the intestine. The NHS notes that the operation usually takes around 2 hours.

As well as limiting how much you can eat, a bypass changes how your body absorbs food and regulates hunger. It is particularly effective for improving obesity-related conditions such as type 2 diabetes.

In the UK, the NHS generally considers weight-loss surgery if you have a BMI of 40 or more, or a BMI between 35 and 40 with a condition that could improve with weight loss, such as type 2 diabetes or high blood pressure. People from some ethnic backgrounds, including South Asian, Chinese, Middle Eastern, Black African and African-Caribbean backgrounds, may be considered at a lower BMI.

International guidelines from the American Society for Metabolic and Bariatric Surgery (ASMBS) and IFSO recommend surgery for people with a BMI over 35, and suggest considering it from a BMI of 30 for people with metabolic disease such as type 2 diabetes.

Results vary from person to person and depend on your starting weight, your health and the changes you make after surgery. The ASMBS reports that patients may lose as much as 77% of their excess weight within the first year, depending on the procedure. Gastric bypass is often associated with slightly greater weight loss and a stronger effect on type 2 diabetes, while a sleeve offers a simpler operation with fewer nutritional issues.

Modern weight-loss surgery is considered safe. The ASMBS states that the risk of major complications is about 4% and the risk of death about 0.1%, which is comparable to common operations such as gallbladder removal or joint replacement.

• Both operations: bleeding, infection, leaks from the staple line, blood clots and gallstones.
• Gastric sleeve: new or worsening reflux and heartburn.
• Gastric bypass: vitamin and mineral deficiencies, dumping syndrome, ulcers (especially with smoking or anti-inflammatory painkillers) and small bowel problems.

Your stomach needs time to heal, so you will move through several diet stages over the first weeks. Your team will give you a detailed plan, but it usually looks like this:

1. 1Liquids: clear fluids and protein drinks, taken in small sips.
2. 2Purée: smooth, blended, protein-rich foods.
3. 3Soft foods: foods that are easy to mash with a fork.
4. 4Normal textures: small, balanced meals, eaten slowly and chewed well.

Long term, you will eat much smaller portions, focus on protein, avoid drinking with meals and take supplements. Regular follow-up helps you stay on track and catch deficiencies early.

The right operation depends on your BMI, your medical history, whether you have reflux or type 2 diabetes, and your lifestyle. A bariatric surgeon will review all of this with you. If you are still researching, our weight-loss surgery calculator shows your BMI and likely options in a minute, and our free online assessment can take it from there.