Gastric sleeve vs gastric bypass

In a sleeve gastrectomy, roughly three quarters or more of the stomach is removed, leaving a banana-shaped tube. This limits the volume of food, and removing the part of the stomach that produces much of the hunger hormone ghrelin can reduce appetite.

In a Roux-en-Y gastric bypass, a small pouch is made at the top of the stomach and connected directly to the small bowel further down. Food bypasses most of the stomach and the first section of the small intestine. This limits portion size and changes gut hormone signals that affect appetite and blood sugar.

Weight loss is substantial after both, and in clinical studies the average difference between them is modest, often slightly in favour of bypass. Results depend heavily on long-term eating habits, activity and follow-up. Both operations are tools that need lasting behaviour change.

Type 2 diabetes often improves quickly after either, and sometimes goes into remission, with bypass showing somewhat higher remission in some studies. Reflux is the clearest divider: pre-existing significant reflux generally points toward bypass, as sleeve can aggravate it.

All major abdominal surgery carries risks of bleeding, infection, blood clots and anaesthetic complications. Specific to these operations are leaks from staple lines, narrowing or stricture, gallstones due to rapid weight loss, and for bypass an internal hernia and dumping syndrome after sugary food. Long-term, the risk of vitamin and mineral deficiency is real and requires lifelong blood monitoring and supplements.

Mental health, eating behaviour, alcohol use and the support available after surgery influence results. Specialist teams assess these before surgery, and quality standards advise follow-up care for at least two years, with annual monitoring thereafter.

NICE NG246 says adults with a BMI of 40 or more, or 35 to 39.9 with a significant health condition, should be offered referral for assessment for bariatric surgery, with expedited assessment for people with a BMI of 35 or more and recent-onset type 2 diabetes. The multidisciplinary team then recommends a procedure, considering reflux, diabetes, previous surgery, medication absorption and patient preference.

Where there is no strong reason to prefer one, patient preference and surgical experience carry weight, since both are accepted procedures with good outcomes in experienced centres.

• Significant acid reflux or hiatus hernia: ask whether bypass is safer for you.

• Type 2 diabetes on multiple medicines: discuss which procedure the team expects to help most.

• Concern about long-term vitamin deficiency or difficulty attending follow-up: a sleeve may carry less deficiency risk, but follow-up remains essential.

• Taking medicines that need reliable absorption: discuss with the team how each operation affects them.

• Previous abdominal surgery or complex anatomy: your surgeon may favour one approach for technical reasons.

Neither operation is an easy or cosmetic option; they require permanent changes to eating and ongoing monitoring. Weight regain can occur with either, and a sleeve is not the "mild" operation in terms of commitment.

It is also a misconception that surgery replaces the need for assessment of underlying causes such as sleep apnoea, thyroid disease or medicines that raise weight.