Health & Safety
Bariatric Surgery Explained: Who Qualifies, Types and Recovery
Weight loss surgery is a major treatment for severe obesity, with lifelong changes afterward. Here's what it means, who qualifies in the US and UK, how the main operations compare, and the risks to weigh.
In brief: bariatric surgery is an operation on the stomach or intestines that helps people with severe obesity lose weight when other treatments haven't worked. It's usually considered at a BMI of 40 or more, or 35 or more with a serious weight-related condition such as type 2 diabetes. The three most common operations are the gastric sleeve, gastric bypass and adjustable gastric band. It needs lifelong changes to eating, activity and vitamin use.
What Bariatric Surgery Means
Bariatric surgery (sometimes named metabolic surgery, or simply weight loss surgery) changes how your digestive system works. Most operations make the stomach much smaller, so you feel full after a small amount of food. Some also reroute the intestine, so your body takes in fewer calories. The NIDDK notes that these changes can also affect gut hormones and bacteria involved in appetite and metabolism.
It's meant for people with obesity who haven't been able to lose enough weight in other ways, such as lifestyle programs or weight loss medication. It isn't a cosmetic procedure, and it doesn't remove the need for healthier habits.
Bariatric Surgery Requirements in the US and UK
The main requirement is a high BMI, usually combined with health problems linked to weight. US and UK criteria are close but not identical:
| Criterion | US (NIDDK, adults) | UK (NHS) |
|---|---|---|
| BMI alone | 40 or more | 40 or more |
| BMI plus a weight-related condition | 35 or more, with a serious problem like sleep apnea, heart disease or type 2 diabetes | 35 to 40, with a condition that could improve with weight loss, such as diabetes, high blood pressure, arthritis or breathing problems |
| Hard-to-control type 2 diabetes | 30 or more | Not listed on this page |
| Some ethnic backgrounds | Not listed | Lower thresholds: 37.5 or more, or 32.5 to 37.4 with a related condition |
| Commitment after surgery | Lifelong healthy habits, medical follow-up and extra vitamins and minerals | Healthy lifestyle changes and regular check-ups |
The NHS's lower thresholds apply to people of Black African, African-Caribbean, Middle Eastern, Chinese, South Asian or other Asian heritage, who face health risks at a lower BMI. NHS availability also varies by area.
Teenagers can sometimes have weight loss surgery too. US guidance says they should be assessed by a specialist team with pediatric expertise, at a BMI of 40, or from 35 if they also have significant health problems caused by obesity.
Example: What a BMI of 35 or 40 Means at 170 cm
BMI is weight in kilograms divided by height in meters squared. For an adult who is 170 cm (5 ft 7 in) tall:
- BMI 35 = 35 × 1.70 × 1.70 = about 101 kg (223 lb)
- BMI 40 = 40 × 1.70 × 1.70 = about 116 kg (255 lb)
So at this height, surgery might be discussed from about 116 kg (255 lb) alone, or from about 101 kg (223 lb) with a serious related condition. Check your own figure with the BMI calculator, and see our healthy BMI chart for what each band means.
Types of Bariatric Surgery
US surgeons most often perform three operations. A fourth, the duodenal switch, is used less often.
| Operation | What happens | Main advantages | Main drawbacks |
|---|---|---|---|
| Gastric sleeve (sleeve gastrectomy) | About 80% of the stomach is removed, leaving a narrow, banana-shaped pouch | More weight loss than a band; intestines untouched; no implant; short hospital stay | Permanent; risk of low vitamins and iron; possible acid reflux or hiatal hernia |
| Gastric bypass (Roux-en-Y) | A small stomach pouch is stapled off and joined to the middle of the small intestine | More weight loss than a band; no implant | Hard to reverse; highest risk of vitamin and iron shortage of the three; may raise the risk of alcohol problems |
| Adjustable gastric band | An inflatable band around the top of the stomach creates a small pouch; the opening is adjusted through a port under the skin | Adjustable and reversible; lowest risk of vitamin shortage; low early surgical risk | Least weight loss; many follow-up visits; band may need removing or replacing |
| Duodenal switch | A sleeve plus a major rerouting of the small intestine | Most weight loss | Highest risk of surgical problems and of vitamin, mineral and protein shortages |
Gastric Sleeve vs Gastric Bypass
These are the two operations most people choose between. Both remove the need for an implant and lead to more weight loss than a band. A bypass also changes the route food takes through the intestine. In one large study cited by the NIDDK, bypass produced greater average weight loss but had more complications in the first month. Bypass also needs follow-up procedures more often than the sleeve. The right choice depends on your health and your surgeon's advice.
Most of these operations are done laparoscopically, through small cuts with a camera, which usually means less pain and faster recovery than open surgery.
How Much Weight Do People Lose?
Results vary by person and by operation. The NIDDK cites one study in which people lost between 38 and 87 lb (about 17 to 39 kg) in the first year across the band, sleeve and bypass. Most regained some weight later, but usually only a small part of what they had lost. Long-term success depends on keeping up healthy eating and activity, not just the operation.
Losing weight can improve many conditions linked to obesity. Our guide to the health risks of obesity covers which ones.
Risks, Side Effects and Recovery
Like any major operation, bariatric surgery carries risks. The NHS describes it as common and safe, but your surgeon will go through the risks with you. Possible problems include:
- Early: bleeding, infection, leg clots that may travel to the lungs, and leaks where the stomach or intestine was joined.
- Later: narrowing of the stomach opening, hernias, gallstones after rapid weight loss, band slipping, and nutrient shortages that can lead to anemia or weak bones.
- Excess skin as weight comes off, which may need further surgery.
- More procedures: the NIDDK reports that about one in three people need a further procedure, surgery or hospital stay within 5 years.
Death from surgery-related problems is rare. In the UK, the usual hospital stay is 1 to 2 days. Recovery takes about 3 to 4 weeks, and regular check-ups continue for 2 years. Diet moves from liquids to soft foods to solids over several weeks, with small meals and lifelong vitamin and mineral supplements.
Limits and When to Get Advice
This guide can't tell you whether surgery is right for you. Start with your doctor, who can refer you to a specialist team. Before surgery you'll usually meet a physician, a dietitian, a psychologist or psychiatrist, and the surgeon.
After surgery, the NHS advises calling emergency services for breathing difficulty or chest pain with leg pain or swelling, severe stomach pain, or vomiting blood. Seek urgent advice for a fever, fast heartbeat, persistent vomiting, trouble swallowing, or a painful, swollen leg.
Frequently Asked Questions
What is the minimum BMI for bariatric surgery?
In the US, surgery may be considered from a BMI of 35 with a serious weight-related condition, or 30 with type 2 diabetes that's hard to control. In the UK, the NHS usually starts at 35 with a related condition, or lower for some ethnic backgrounds. A BMI of 40 or more qualifies on its own in both.
Which type of bariatric surgery is best?
No single operation is best for everyone. The bypass tends to give the most weight loss of the three common types but has more early complications. The sleeve is permanent but avoids rerouting the intestine. The band is reversible but leads to the least weight loss. Your surgeon will recommend one based on your health.
Can you regain weight after bariatric surgery?
Yes, some regain is common. In the study the NIDDK cites, most people put some weight back on over time, though usually a small amount compared with what they lost. Sticking with smaller meals, regular activity, prescribed vitamins and follow-up appointments gives you the best chance of keeping the weight off.
How long is recovery from bariatric surgery?
On the NHS, most people leave hospital 1 to 2 days after surgery and recover over roughly 3 to 4 weeks. Eating returns to normal in stages, from liquids to soft foods to solids, over several weeks. Regular check-ups continue for 2 years, and vitamin and mineral supplements are usually lifelong.
To see whether your BMI is in the range where surgery may be discussed, use the BMI calculator.
Sources
- Potential candidates for weight-loss surgery (NIDDK, NIH)
- Types of weight-loss surgery (NIDDK, NIH)
- Weight-loss surgery side effects (NIDDK, NIH)
- Why weight loss surgery is done (NHS)
- Complications of weight loss surgery (NHS)
- Overweight and obesity in adults: treatments (NHS)
This guide is general information, not medical advice. It was written by the CaloriePro Editorial Team from the sources above; see our editorial policy. Speak to a doctor or registered dietitian before making big changes to your diet, especially if you are pregnant, under 18, or have a medical condition.