1. Definition
Obesity is a chronic, multifactorial condition defined by excess body fat. It’s typically assessed using the Body Mass Index (BMI):
- Overweight: BMI ≥ 25
- Obese: BMI ≥ 30
- Severely obese: BMI ≥ 40.
Different ethnic groups may have lower thresholds due to varying risks. In addition to BMI, waist-to-height ratio (≥ 0.5) is a useful measure, especially for those with BMI under 35, as it highlights excess abdominal fat and its associated risks.
2. Epidemiology
- Obesity is a major public health issue in the UK, affecting around 1 in 4 adults and 1 in 5 children aged 10-11.
- Childhood obesity has also been rising, with 39 million children under 5 globally classified as overweight or obese in 2020
- Childhood obesity often leads to adult obesity and increases the risk of developing chronic diseases earlier in life.
3. Risk Factors
- Genetics: While lifestyle factors are crucial, genetics also play a role, influencing fat storage and energy conversion
- Environment: Sedentary lifestyles, high-calorie diets, urbanisation, poor sleep, certain medications (e.g. steroids), and limited access to healthy foods all contribute to obesity.
4. Causes
- For most individuals, obesity is the result of consuming more calories than are expended through physical activity, with excess energy being stored as fat
- Modern lifestyles often encourage overeating, particularly of cheap, high-calorie and/or ultra-processed foods, alongside reduced physical activity.
Medical causes
In some cases, obesity may be driven by:
- Medications: Such as corticosteroids, antidepressants, and antipsychotics
- Brain structure/function changes: E.g. tumours or infections affecting the hypothalamus
- Endocrine disorders: Such as Cushing syndrome, hypothyroidism, or hyperinsulinism.
5. Symptoms
Obesity itself doesn’t produce specific symptoms, but it is associated with symptoms related to its complications, such as joint pain, difficulty breathing (due to obstructive sleep apnoea), and reduced mobility.
6. Diagnosis
Obesity is diagnosed primarily using BMI, with additional assessments like waist-to-height ratio to evaluate abdominal fat.
7. Treatment
- Obesity management includes lifestyle changes (diet and exercise), medication, and in severe cases, bariatric surgery
- A multidisciplinary approach with dietitians, psychologists, and medical professionals generally provides the best outcomes.
Medications
- GLP-1 Agonists: These drugs help with weight management and diabetes. The most well-known is semaglutide, which is available as:
- Ozempic (for diabetes management)
- Wegovy (for weight loss, available on the NHS)
- Rybelsus (oral form for diabetes).
Other GLP-1 agonists include exenatide (Bydureon), liraglutide (Victoza), and dulaglutide (Trulicity). Tirzepatide (Mounjaro) is another emerging option for weight management.
8. Complications
Obesity significantly increases the risk of:
- Type 2 diabetes
- Ischaemic heart disease (IHD)
- Hypertension
- Obstructive sleep apnoea (OSA)
- Infertility
- Certain cancers (e.g. breast, bowel)
- Musculoskeletal issues (e.g. osteoarthritis leading to joint replacements).
Psychological impact
Obesity is closely linked with mental health problems, such as depression and anxiety. Social stigma and discrimination often worsen the psychological burden.
9. Prognosis
- Without treatment, obesity tends to worsen over time
- The risk and severity of complications increase with the amount and distribution of body fat
- Weight loss is often challenging to maintain, with most individuals regaining weight within five years, necessitating ongoing management similar to other chronic diseases.
Stopping anti-obesity medication often results in weight regain, so lifelong management may be necessary.
10. Prevention
- Preventing obesity requires a combination of healthy eating, regular exercise, and behavioural changes
- Public health measures also play a key role in promoting healthier environments and lifestyles, particularly by improving access to healthier foods and encouraging physical activity.
Other considerations
- Global variation: Obesity prevalence varies across regions, with higher rates in high-income countries but a rising trend in low- and middle-income countries due to lifestyle changes.
- Economic impact: Obesity places a significant financial burden on healthcare systems. In the UK, it is a major driver of healthcare costs and productivity loss.
Addressing obesity requires a broad approach, integrating medical management, public health initiatives, and individual lifestyle changes to reduce its growing burden on society.
