Key Facts

Bariatric surgery is the most effective treatment for morbid obesity, producing sustained weight loss, resolution of comorbidities, and reduced mortality. The NHS performs approximately 6,000-7,000 bariatric procedures annually, though demand far exceeds provision.

Epidemiology

Obesity (BMI ≥30) affects approximately 28% of adults in England. Severe obesity (BMI ≥40) affects approximately 3%. The UK has among the highest obesity rates in Europe. Obesity costs the NHS an estimated £6.5 billion annually.

Aetiology

Obesity is a multifactorial chronic disease involving genetic susceptibility, environmental factors (calorie-dense diet, sedentary lifestyle), psychological factors, and neuroendocrine regulation. Bariatric surgery addresses obesity through restriction, malabsorption, or both, and through favourable changes in gut hormones (GLP-1, PYY, ghrelin).

Pathophysiology

Mechanisms of weight loss after bariatric surgery:

• Restriction: Reduced gastric volume limits food intake (sleeve, band)
• Malabsorption: Bypassed small bowel reduces calorie absorption (RYGB, BPD-DS)
• Hormonal: Increased GLP-1 and PYY (satiety), reduced ghrelin (hunger); improved insulin sensitivity
• Bile acid changes: Altered enterohepatic circulation improves glucose metabolism
• Gut microbiome: Post-surgical changes in microbiota contribute to metabolic improvements

Indications for Bariatric Surgery (NICE CG189)

• BMI ≥40 kg/m² (or ≥35 with comorbidities) after failed non-surgical management
• BMI ≥35 with recent-onset type 2 diabetes — consider expedited referral
• BMI ≥50 — consider as first-line treatment
• Asian patients — lower BMI thresholds apply (≥37.5 or ≥32.5 with comorbidities)

Obesity-Related Comorbidities

• Type 2 diabetes, hypertension, dyslipidaemia
• Obstructive sleep apnoea
• NASH/NAFLD
• Osteoarthritis, GORD
• Polycystic ovarian syndrome, subfertility

Post-Operative Complications

• Early: Anastomotic leak (1-5%), bleeding, PE, staple line failure
• Late: Dumping syndrome, nutritional deficiencies, internal hernia, gallstones, weight regain

Red Flags

• Tachycardia post-operatively (HR >120) — suspect anastomotic leak until proven otherwise
• Severe abdominal pain with vomiting — consider internal hernia (can cause closed-loop obstruction)
• Rapid weight loss with hair loss, fatigue — screen for nutritional deficiencies
• Hypoglycaemic episodes post-RYGB — consider nesidioblastosis

Bedside

• BMI calculation: Height and weight; waist circumference
• Epworth Sleepiness Scale: Screen for OSA
• PHQ-9/GAD-7: Screen for depression/anxiety

Bloods

• HbA1c, fasting glucose: Diabetes screening/monitoring
• Lipid profile: Cardiovascular risk
• LFTs: NAFLD screening
• TFTs: Exclude hypothyroidism
• Nutritional screen: Iron, ferritin, B12, folate, calcium, vitamin D, PTH, zinc, copper, selenium
• FBC: Anaemia

Imaging

• USS abdomen: Gallstones, liver assessment
• OGD: Pre-operative — exclude hiatus hernia, H. pylori, Barrett's
• DEXA scan: Baseline bone density if risk factors
• Sleep study/polysomnography: If OSA suspected

Special Tests

• Cardiopulmonary exercise testing (CPET): For high-risk patients
• Echocardiogram: If cardiac disease suspected
• Psychiatric/psychological assessment: Mandatory pre-operative — assess eating behaviour, expectations, mental health

Non-pharmacological

• Tier 3 weight management service: Minimum 6-12 months supervised diet/lifestyle programme before surgery (unless fast-tracked)
• Pre-operative diet: 2-4 week liver shrinkage diet (very low calorie ~800 kcal/day)
• Post-operative dietary progression: Liquids → puree → soft → solid over 6-8 weeks
• Lifelong follow-up: Annual nutritional bloods, dietitian review, psychological support

Pharmacological

• Lifelong supplementation: Multivitamin, calcium 1000-1500mg + vitamin D 800-2000 IU/day, B12 (IM if malabsorptive procedure), iron as needed
• PPI: Omeprazole 20mg OD for 6-12 months post-bypass (marginal ulcer prophylaxis)
• Ursodeoxycholic acid 300mg BD: For 6 months post-op to reduce gallstone formation
• VTE prophylaxis: Enoxaparin 40-60mg SC OD (weight-adjusted), extended 14-28 days

Surgical/Interventional

• Roux-en-Y gastric bypass: Small gastric pouch anastomosed to jejunum; gold standard for T2DM
• Sleeve gastrectomy: Resection of ~80% of stomach along the greater curvature; most common globally
• Adjustable gastric band: Least invasive, but poorest long-term results; rarely performed now
• One-anastomosis gastric bypass (OAGB): Emerging procedure, growing evidence base
• Endoscopic options: Intragastric balloon, endoscopic sleeve gastroplasty (less invasive, less durable)

Referral Criteria

• BMI ≥40 (or ≥35 with comorbidities) after failed conservative management — refer to Tier 3/4 bariatric service
• BMI ≥50 or ≥35 with recent-onset T2DM — consider expedited referral
• Post-operative complications — emergency surgical assessment

• Excess weight loss: RYGB 60-70%, sleeve 50-60%, band 40-50% at 5 years
• T2DM remission: 60-80% after RYGB, 50-60% after sleeve (STAMPEDE trial)
• Mortality reduction: 40% reduction in all-cause mortality (SOS study, 20-year follow-up)
• 30-day mortality: <0.5% in specialist centres
• Weight regain: 20-30% of patients experience significant weight regain by 5-10 years
• Revision surgery: Required in approximately 5-15% for complications or weight regain

Comparison of Bariatric Procedures

Landmark Trials