Severe obesity with comorbidity
By The Treatment Registry editors
Patients with BMI ≥40, or ≥35 with significant comorbidity (type 2 diabetes, sleep apnoea, hypertension), may be candidates for bariatric (weight-loss) surgery. The treatment ladder runs through medical management, modern weight-loss pharmacotherapy, endoscopic procedures, and definitive surgery. Surgical options have different mechanisms and trade-offs around weight loss, reflux, and reversibility.
Clinical overview
Signs and symptoms
Obesity is a condition in which excess body fat has accumulated to an extent that can have negative effects on health, and it is a major cause of disability. It is classified using body mass index, with a BMI over 30 kg/m2 defined as obese; severe obesity denotes a BMI of 40 or above, or 35 or above where a significant comorbidity is present. The clinical burden is dominated by associated disease: obesity is correlated with cardiovascular disease, type 2 diabetes, obstructive sleep apnoea, certain cancers, and osteoarthritis. In patients considered for bariatric surgery, it is this comorbidity load, alongside the degree of excess weight, that characterises the presentation rather than any single symptom.
Causes and risk factors
Obesity has individual, socioeconomic, and environmental causes. The fundamental driver is a sustained positive energy balance, where energy intake from food exceeds energy expenditure, combined with a resetting of the body's weight set point at a higher value. Excess appetite for palatable, high-calorie food, low physical activity, automation, urbanisation, and increased reliance on cars are all implicated, alongside genetic susceptibility, certain medications such as atypical antipsychotics, mental disorders, endocrine disorders, insufficient sleep, and exposure to endocrine-disrupting chemicals. At a biological level, appetite-regulating hormones such as leptin and ghrelin act on the hypothalamus; deficient leptin signalling, through leptin deficiency or resistance, leads to overfeeding and may account for some genetic and acquired forms of obesity.
How it is diagnosed
Obesity is assessed using body mass index, a person's weight divided by the square of their height. A BMI over 30 kg/m2 is defined as obese and the range 25 to 30 kg/m2 as overweight, though some East Asian countries apply lower thresholds. Within this classification, severe obesity is identified at a BMI of 40 or above, or 35 or above in the presence of a significant comorbidity such as type 2 diabetes, sleep apnoea, or hypertension, which is the threshold at which bariatric surgery may be considered.
Who it affects
In 2022, over 1 billion people lived with obesity worldwide (879 million adults and 159 million children), and the World Health Organization formally recognised obesity as a global epidemic in 1997. The CDC reported that the prevalence of obesity among US adults aged 20 and over was 41.9% from 2017 to March 2020, with severe obesity at 9.2% over the same period. Severe obesity in the United States, Australia, and Canada is increasing faster than the overall rate of obesity. Prevalence rises with age at least up to 50 or 60 years, and globally there are more obese women than men.
Clinical overview sourced from encyclopaedic medical reference; see sources below. General information only — not a substitute for individual clinical assessment.
Treatment ladder
Conservative options are first-line where appropriate; surgical options are typically reserved for cases where lower-tier options are unsuitable or have failed. Decisions are individual and depend on clinical assessment.
Conservative
- Multidisciplinary medical weight management
Coordinated dietetic, behavioural, and exercise support. Effective in some patients but historically modest long-term outcomes for severe obesity.
- GLP-1 receptor agonist therapy
Semaglutide, tirzepatide, and related agents producing 15-25% body-weight reduction in many patients. Continuing evidence base; weight typically regained on cessation.
Procedural
- Endoscopic gastric balloon
Saline- or air-filled balloon placed endoscopically for 6 months. Modest weight loss; suitable as a bridge therapy or for patients ineligible for surgery.
- Endoscopic sleeve gastroplasty
Endoscopic suturing to reduce stomach volume without surgical resection. Less established evidence than surgical alternatives.
Surgical
- Sleeve gastrectomy · View procedure page
Resection of approximately 75% of the stomach to create a tubular gastric remnant. The most commonly performed bariatric operation worldwide; durable weight loss but elevated reflux risk in some patients.
- Roux-en-Y gastric bypass
Creation of a small gastric pouch and a Roux limb of small bowel, bypassing most of the stomach and proximal small bowel. Greater weight loss than sleeve in many series; better resolution of reflux and type 2 diabetes; technically more demanding.
- Mini gastric bypass (one-anastomosis)
Single-anastomosis variant of bypass. Shorter operating time; concerns about long-term bile reflux remain debated.
Related procedures
Sources
- [1]IFSO — Clinical Guidelines for Bariatric and Metabolic Surgery — ifso.com(accessed 2026-05-09)
- [2]Wikipedia — Obesity — en.wikipedia.org(accessed 2026-07-24)
- [3]Cochrane Database — Surgery for weight loss in adults — cochranelibrary.com(accessed 2026-05-09)
Sources marked “on file” are held by The Treatment Registry but are not publicly accessible.