Bariatric & metabolic surgery for medical students

Written and clinically reviewed by Dr. Mohammed Maree, consultant minimally invasive and bariatric surgeon, Al-Makassed Hospital, Jerusalem, and Assistant Professor of Surgery, Al-Quds University. Last updated 1 November 2026.

Bariatric and metabolic surgery is assessed as a whole-patient problem, not a weight problem: the duration of obesity and what has already been tried, the comorbidities that the operation is expected to treat (type 2 diabetes, obstructive sleep apnoea, reflux, hypertension, fatty liver), eating pattern and reflux symptoms, mental health, and what the patient expects the operation to achieve. Reflux history in particular changes the operation chosen.

Who is a candidate?

The 2022 ASMBS and IFSO guidelines recommend metabolic and bariatric surgery for adults with a BMI of 35 kg/m² or more, whether or not they have a related disease, and suggest considering it from a BMI of 30 in people with metabolic disease such as type 2 diabetes. In Asian populations the thresholds are lower, because metabolic risk rises at a lower BMI.

The common operations

Operation	What it does	Points to know
Sleeve gastrectomy	Removes most of the greater curve of the stomach, leaving a narrow tube	The most performed operation worldwide. Can worsen or cause reflux.
Roux-en-Y gastric bypass	A small gastric pouch joined to a Roux limb of jejunum	Often preferred when there is significant reflux. Risk of marginal ulcer and internal hernia.
One-anastomosis gastric bypass	A long, narrow pouch with a single loop anastomosis	Technically simpler than a Roux-en-Y bypass. Bile reflux and nutritional deficiency need watching.

Complications to recognise on the ward

Red flags after bariatric surgery

Tachycardia — a persistent heart rate above about 120 is a leak until proven otherwise, even when the abdomen feels soft. Obese patients often have few abdominal signs.
Bleeding — from the staple line, into the lumen or the abdomen.
Persistent vomiting — stenosis or a twist; and in any patient vomiting for weeks, give thiamine before glucose to prevent Wernicke encephalopathy.
Colicky pain months or years after a bypass — an internal hernia until proven otherwise, even with a normal CT.
Long-term deficiencies — iron, vitamin B12, folate, vitamin D and calcium. Lifelong supplements and follow-up.

Cover of Metabolic and Bariatric Surgery, Endobariatrics, and AI (IntechOpen)

Peer-reviewed chapter · IntechOpen · 2026

AI-Enhanced Bariatric and Endobariatric Surgery

A review of artificial intelligence across bariatric and endoscopic weight-loss interventions, synthesising roughly 300 studies from 2018 to 2025 — what the models can already predict, and what they still cannot.