Background Information
Aetiology
Overweight and obesity are caused by a chronic imbalance between energy intake and energy expenditure, resulting in excess body fat accumulation.
Aetiology is multi-factorial: [Ref1][Ref2]
- Genetic predisposition (usually polygenic and interacts with environmental factors)
- Environmental contributors
- Excessive caloric intake
- Consumption of ultra-processed foods and sugar-sweetened beverages
- Low physical activity
- Low socioeconomic status
- Chronic stress
- Insufficient sleep
Medical causes of overweight and obesity: [Ref1][Ref2]
- Depression
- Hypothyroidism
- Cushing’s syndrome
- Binge eating disorder
Medications associated with weight gain: [Ref1][Ref2]
- Certain diabetes medications (insulin, sulfonylurea, pioglitazone) (other medications are either weight-neutral or promote weight loss)
- Antipsychotics (esp. olanzapine)
- Systemic corticosteroids
- Antidepressants (e.g. amitriptyline, mirtazapine)
- Antiepileptics (e.g. gabapentin, carbamazepine)
- Beta blockers
- Protease inhibitors
Complications
Identification and Assessment
Methods of Measurement
NICE recommends BMI as a practical measure of overweight and obesity.
- BMI: weight (kg) / (height in m)2
NICE also recommends measuring waist-to-height ratio in those with BMI <35 kg/m2
- Waist-to-height ratio is a practical estimate of central adiposity, which can be used to assess and predict health risks
Interpretation (Adults)
BMI
| Classification | BMI range (kg/m2) |
|---|---|
| Healthy weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obesity class 1 | 30.0 – 34.9 |
| Obesity class 2 | 35.0 – 39.9 |
| Obesity class 3 | ≥40.0 |
NICE recommends lower BMI thresholds in people with South Asian, Chinese, other Asian, Middle Eastern, Black African, and African-Caribbean backgrounds as they are prone to central adiposity and their cardiometabolic risk occurs at lower BMI:
- Overweight: BMI 23 – 27.4 kg/m2
- Obesity: BMI ≥27.5 kg/m2
- Obesity class 2 and 3: minus 2.5 kg/m2 from the above thresholds
Note that BMI is NOT a direct measure of central adiposity.
BMI should be interpreted with caution in:
- Adults with high muscle mass
- ≥65 y/o
Central Adiposity (Waist-to-Height Ratio)
Central adiposity should be classified based on waist-to-height ratio
The following waist-to-height classification can be used for people with BMI <35 kg/m2 of both sexes and all ethnicities, including adults with high muscle mass.
| Classification | Waist-to-height ratio range |
|---|---|
| Healthy | 0.4 – 0.49 |
| Increased | 0.5 – 0.59 |
| High | ≥0.6 |
Interpretation (Children and Young People)
BMI
Centiles and standard deviations should be used to classify BMI.
| Classification | BMI (centile and SD) |
|---|---|
| Overweight | BMI 91st centile + 1.34 SD |
| Clinical obesity | BMI 98th centile + 2.05 SD |
| Severe obesity | BMI 99.6th centile + 2.68 SD |
Central Adiposity (Waist-to-Height Ratio)
Central adiposity should be classified based on waist-to-height ratio
The classification is the same as adults:
| Classification | Waist-to-height ratio range |
|---|---|
| Healthy | 0.4 – 0.49 |
| Increased | 0.5 – 0.59 |
| High | ≥0.6 |
Management
Conservative / General Management
Key point is employing a multicomponent management strategy with long-term support, including:
- Increase physical activity changes, and
- Reduced-calorie diet
Pharmacological Management
All medicines for weight management should be used alongside a reduced-calorie diet and increased physical activity.
| Drug | Class | Indications* | Route | Important side effects |
|---|---|---|---|---|
| Orlistat | Lipase inhibitor |
|
Oral capsule |
|
| Tirzepatide | GLP-1 and GIP agonist |
|
Weekly subcutaneous injection |
|
| Semaglutide | GLP-1 agonist |
|
||
| Liraglutide |
|
Daily subcutaneous injection |
*For tirzepatide, semaglutide and liraglutide, NICE recommends using lower BMI thresholds (usually reduced by 2.5 kg/m2) for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean ethnic backgrounds.
If <5% of initial body weight has been lost, this is generally considered a threshold to stop treatment, depending on the medication-specific review timeframe:
- 6 months: tirzepatide and semaglutide
- 3 months: liraglutide and orlistat
Pregnancy
Medications used to manage obesity should NOT be used during pregnancy
The use of contraception while taking these medications is generally recommended.
Children and Young People
Medications are NOT generally recommended for those <12 y/o
- Only consider in exceptional circumstances, if severe comorbidities are present
Surgical Management
Referral Criteria
Refer to specialist overweight and obesity management service to assess for bariatric surgery eligibility if:
- BMI ≥40 kg/m2 or BMI 35-39.9 kg/m2 + significant health conditions
Examples outlined by NICE:
- Cardiovascular disease
- Hypertension
- Idiopahic intracranial hypertension
- Metabolic dysfunction-associated steatotic liver disease +/- steatohepatitis
- Obstructive sleep apnoea
- Type 2 diabetes
- Patient agrees to necessary long-term follow-up after surgery
Early assessment for bariatric surgery should be considered in:
- BMI 30-34.9 kg/m2, and
- Recent-onset type 2 diabetes (diagnosed <10 years), and
- Receiving, or will receive, assessment in a specialist overweight and obesity management service
Consider referral for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African–Caribbean background using a lower BMI threshold (reduced by 2.5 kg/m2)
Surgical Options
NICE did not make any specific recommendations on which surgical interventions to use, but it is important to know about the commonly used bariatric surgeries.
| Procedure | Type | Mechanism | Disadvantages |
|---|---|---|---|
| Sleeve gastrectomy | Restrictive | Removes ~80% of the stomach (greater curvature) |
|
| Adjustable gastric banding | Inflatable band around the upper stomach, adjustable via subcutaneous port |
|
|
| Roux-en-Y gastric bypass | Restrictive + malabsorptive | A small stomach pouch is created and connected to the intestine to bypass the duodenum and proximal jejunum |
|
| Biliopancreatic diversion with duodenal switch | Sleeve gastrectomy + bypass of most of the small intestine |
|