Adult Obesity: Diagnosis and Management in the UK

What defines obesity in adults?

  1. Why is obesity considered a disease and not just a lifestyle choice?

  2. What are the current obesity rates in the UK and globally?

  3. What causes obesity, and how do genetics play a role?

  4. What complications are associated with obesity?

  5. How is obesity diagnosed in different ethnic groups?

  6. What role do lifestyle interventions play in weight management?

  7. When should pharmacotherapy be considered?

  8. Who is eligible for bariatric surgery on the NHS?

  9. How effective are different treatment modalities?

  10. How should GPs approach conversations around weight?

  • True

  • True

  • False

  • False

  • True

  • False

  • True

  • True

  • False

  • False (the risk plateaus or may appear to decline due to survivorship bias)

Introduction

"Obesity is a chronic, progressive and relapsing disease, characterised by the presence of abnormal or excess adiposity that impairs health and social wellbeing.”
Royal College of Physicians

"Obesity is a complex multifactorial disease defined by excessive adiposity and is linked to an increased risk for many noncommunicable diseases, including CVDs, 13 types of cancer, T2D and chronic respiratory diseases including OSA.”
World Health Organization

UK and Global Obesity Context

Obesity is a significant and rising public health issue in the UK.
Currently, 29% of adults in England live with obesity, and 64% have either overweight or obesity.
The economic burden of obesity is considerable:

  • £11.4 billion per year in direct costs to the NHS

  • £74.3 billion annually in broader societal impacts from lost productivity, unemployment, and social care dependency

These costs are projected to rise, placing growing strain on public services and the wider economy.

International Comparisons

The UK is not alone in facing an obesity epidemic. Globally, over 890 million adults are living with obesity—a number expected to surpass 1 billion by 2030. Prevalences are depicted in the chart below; USA leads high-income countries with 42% adult obesity prevalence. These figures highlight the global scale of the challenge. However, the UK's integrated NHS structure offers a unique opportunity to implement comprehensive and equitable prevention, pharmacological, and surgical interventions.

Obesity Prevalence (Percentage)

Pathophysiology and Causes

Obesity results from a sustained energy imbalance influenced by:

Genetics: Polygenic traits affect appetite regulation and energy use; monogenic obesity (e.g., MC4R mutations) is rare cause

Neuroendocrine Factors: Hormones like leptin, ghrelin, and incretins modulate hunger and energy expenditure.

Environment: Obesogenic environments, stress, poor sleep, and endocrine-disrupting chemicals contribute.

Inflammation: Adipose tissue dysfunction promotes chronic low-grade inflammation and insulin resistance.

Complications of Obesity

  1. Metabolic: Type 2 diabetes, dyslipidaemia, hypertension, metabolic-associated steatotic liver disease (MASLD).

  2. Cardiovascular & Renal:Increased risk of heart failure, CKD, atrial fibrillation.

  3. Respiratory & Sleep: OSA, restrictive lung disease, sleep disorders.

  4. Cancer: 13 obesity-related cancers: Breast (postmenopausal), Endometrial, Colorectal, Kidney, Pancreatic, Oesophageal adenocarcinoma, Gallbladder, Liver, Ovarian, Stomach, Thyroid, Multiple myeloma, and Meningioma.

  5. Musculoskeletal: Osteoarthritis.

  6. Psychological: depression, weight stigma.

  7. All-Cause Mortality: A 30% increase in all-cause mortality is observed for each 5 kg/m² increment in BMI, particularly valid in the range of BMI 25–40 kg/m². Outside this range, the relationship may be attenuated due to reverse causality at low BMI and survivorship bias at high BMI.

Diagnosis

 

White ethnicity
Healthy weight
Overweight
Obesity class 1
Obesity class 2
Obesity class 3

BMI (Asian and Black ethnic groups)
18.5 to 22.9
23 to 27.4
27.5 to 32.4
32.5 to 37.4
37.5 or more

BMI (White ethnic group)
18.5 to 24.9
25 to 29.9
30 to 34.9
35 to 39.9
40 or more

 

Adjusted thresholds:
For Black, Asian and other ethnic groups, adopt a lower BMI threshold (reduced by 2.5 kg/m²).
These groups are prone to central adiposity and their cardiometabolic risk occurs at lower BMI than in people from other family backgrounds.

Waist-to-height ratio (WHtR):
A practical measure of central adiposity and cardiometabolic risk, especially useful for those with BMI <35 kg/m².
Use NHS calculator and measure waist circumference just above the umbilicus.
Healthy: 0.4–0.49
Increased risk: 0.5–0.59
High risk: ≥0.6

WHtR may outperform BMI in predicting cardiometabolic risk, particularly in ethnically diverse populations. It provides a more direct assessment of visceral adiposity, which is strongly linked with insulin resistance, dyslipidaemia, and hypertension. In multi-ethnic cohorts, WHtR has shown better sensitivity and specificity for future diabetes and cardiovascular events compared to BMI alone.

Investigations

Category Recommended Tests Rationale / Notes
Metabolic / Cardiovascular Blood pressure, Fasting lipid profile, QRISK3 score Cardiovascular risk assessment and statin eligibility
Glycaemic status HbA1c, Fasting plasma glucose Screening for type 2 diabetes or prediabetes
Liver function ALT, AST, GGT, Fib-4 score, Liver ultrasound Assess for MASLD/NAFLD, common in obesity
Renal function Urea, creatinine, eGFR, Urinalysis (ACR) Evaluate kidney function, especially with hypertension or diabetes
Endocrine TSH, ± FT4, consider 24hr urinary cortisol Exclude hypothyroidism or Cushing’s syndrome if clinically indicated
Haematological Full blood count Detect anaemia or chronic inflammation
Reproductive hormones (if indicated) Men: Testosterone, SHBG; Women: LH, FSH, Estradiol (if indicated) Investigate for hypogonadism, PCOS, or amenorrhoea if symptomatic
Sleep assessment STOP-Bang questionnaire, ± Sleep study (if OSA suspected) OSA is common and underdiagnosed in obesity
Psychological PHQ-9, GAD-7 Mental health comorbidities may impact weight and engagement

Management Strategies

Lifestyle Interventions

Overall Effectiveness: 4–9% weight loss at 1 year; ~2–3% sustained at 5 years

Diet
Keep the person's total energy intake below their energy expenditure (also called an energy deficit or calorie deficit).
This could be done by lowering specific macronutrient content (e.g.low-fat or low-carbohydrate diets) or using other methods to limit overall energy intake (e.g. meal replacement)

Physical activity
To maintain health: Each week, adults should accumulate at least 150 minutes (2 1/2 hours) of moderate intensity activity (such as brisk walking or cycling); or 75 minutes of vigorous intensity activity (such as running).
To prevent obesity: most people may need to do 45 to 60 minutes of moderate-intensity physical activity a day, particularly if they do not reduce their energy intake.
To prevent weight regain: People who have lived with obesity and have lost weight may need to do 60 to 90 minutes of activity a day to avoid regaining weight

Behavioural support
CBT, motivational interviewing

NHS funded Structured programmes

NHS Better Health website advice on lifestyle changes, such as diet, physical activity, quitting smoking and drinking less.
NHS Digital Weight Management Programme is for people with a diagnosis of diabetes (type 1 or type 2), hypertension, or both and a BMI ≥ 30 kg/m² (or BMI ≥27.5 kg/m² if Black, Asian and other ethnic groups).
NHS Diabetes Prevention Programme Adults with non-diabetic hyperglycaemia: HbA1c 42 to 47 mmol/mol (6.0% to 6.4%). NHS Type 2 Diabetes Path to Remission Programme
Over a 12-week period, participants replace all normal meals with soups and shakes providing a daily total of 800 kcal.
It is for adults aged 18 to 65, diagnosed with type 2 diabetes within the last 6 years, and have a BMI over 27 kg/m² (White ethnic groups) or over 25 kg/m² (Black, Asian and other ethnic groups).

NHS tiered care weight management services (adapted from Obesity Empowerment Network)

  • Tier 1—Universal services (such as public health or population-wide interventions)

  • Tier 2—Community multicomponent weight management services

  • Tier 3—Specialist weight management services (multidisciplinary team AND weight loss medicines)

  • Tier 4—Specialist weight management services (multidisciplinary team AND weight loss medicines & bariatric surgery)

Pharmacotherapy

IMPORTANTLY: All medicines for weight management should be used alongside a reduced-calorie diet and increased physical activity.

Overall effectiveness:
Semaglutide: 12.5% weight loss (non-diabetic); 6.2% (with T2D)
Tirzepatide: 17.8% (non-diabetic); 11.6% (T2D)

  • GLP-1 RA: Glucagon-like peptide-1 receptor agonist (e.g. Semaglutide, licensed as Ozempic®, type 2 diabetes; Wegovy®, for weight management; Rybelsus®, type 2 diabetes )

  • GIP/GLP-1 RA: Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist (e.g. Tirzepatide (Mounjaro®), licensed for type 2 diabetes and weight management).
    Incretin mimetics: hormones released by the gut in response to food consumption, specifically glucose and fat.

  • GLP-1, is an endogenous incretin, that exerts several effects in the body:

    Stimulates insulin release
    Reduces hepatic glucose generation
    Delays food absorption and gastric emptying
    Reduces appetite

  • Due to acting on the same pathway, DPP-4 inhibitors (for example, alogliptin, linagliptin, sitagliptin, saxagliptin and vildagliptin) and GLP-1 receptor agonists (including tirzepatide) should not be used at the same time.

 
 
Feature Tirzepatide (Mounjaro®) Semaglutide (Wegovy® / Ozempic® / Rybelsus®)
Type of drug GIP/GLP-1 RA GLP-1 RA
NICE TA TA1026 (Dec 2024) TA875 (Mar 2023)
Eligibility BMI ≥35 kg/m² (or adjusted for ethnicity) + ≥1 comorbidity BMI ≥35 (or adjusted for ethnicity) + ≥1 comorbidity,OR,BMI 30–34.9 kg/m² & meets Tier 3/4 criteria
Prescribing Primary or specialist care Specialist care only
Route/Frequency Weekly SC injection Weekly SC injection
Pregnancy Avoid. Use contraception. Avoid. Use contraception.
Pregnancy Planning Stop 1 month before Stop 2 months before
Treatment stop rule <5% loss at 6 months <5% loss at 6 months
Delayed gastric emptying Yes – risk of aspiration during anaesthesia Yes – risk of aspiration during anaesthesia
Adverse effects GI upset, nausea, pancreatitis GI upset, nausea, pancreatitis
 

Adjusted for ethnicity: For tirzepatide or semaglutide, use 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.

Weight-related comorbidities that qualify for Tirzepatide, according to NHS England:
Hypertension
Dyslipidaemia
Obstructive sleep apnoea
Cardiovascular disease
Type 2 diabetes mellitus.
[However, missing from this list are other important conditions, such as Pre-diabetes, NAFD].

*People with type 2 diabetes can be prescribed tirzepatide (Mounjaro®) for obesity or for glycaemic management in type 2 diabetes if they meet the criteria set out in either:
a) Tirzepatide (Mounjaro®) for managing overweight and obesity (NICE TA1026)
b) Tirzepatide (Mounjaro®) for treating type 2 diabetes (NICE TA924).

Bariatric Surgery

Effectiveness:** 25–30% weight loss sustained; T2D remission; mortality benefit

Bariatric surgery is a highly effective intervention for individuals with severe or complicated obesity, offering sustained weight loss, remission of type 2 diabetes, and reduction in all-cause and cardiovascular mortality.

NICE Referral Criteria

There is no requirement for patients to have failed all non-surgical approaches or to be under Tier 3 care prior to referral for surgical assessment. Offer referral for a comprehensive assessment by a multidisciplinary specialist obesity service to determine surgical eligibility if the individual:

  • Has a BMI ≥40 kg/m², or

  • Has a BMI 35–39.9 kg/m² with one or more obesity-related comorbidities, such as:

    • Type 2 diabetes (eligible for expedited assessment if diabetes is diagnosed within 10 years)

    • Cardiovascular disease or hypertension

    • Obstructive sleep apnoea

    • Idiopathic intracranial hypertension

    • Non-alcoholic fatty liver disease (NAFLD or MASLD)

Ethnicity-based adjustment: For individuals of South Asian, Chinese, Middle Eastern, Black African or African-Caribbean descent, reduce BMI thresholds by 2.5 kg/m² due to elevated cardiometabolic risk at lower adiposity levels.

 
Procedure Total Body Weight Loss (@ 1 year) Invasiveness Durability T2D Remission Typical Use Case
Roux-en-Y Gastric Bypass (RYGB) 30–35% Laparoscopic surgery High (≥10 years) High Severe obesity or metabolic disease
Sleeve Gastrectomy (SG) 25–30% Laparoscopic surgery High Moderate–High Common first-line surgical option
Endoscopic Sleeve Gastroplasty (ESG) 15–20% Endoscopic (oral) Moderate (≥2 years) Moderate Moderate obesity, lower surgical risk
Intragastric Balloon (IGB) 10–15% Endoscopic (oral) Low (temporary) Low Short-term use with diet programmes
Gastric Balloon Pill (Elipse) 10–14% Capsule (no scope) Low (4 months) Low Temporary, non-invasive preference

Good Practice Points

Ask permission before discussing weight
Use non-stigmatising language
Offer evidence-based interventions early
Recognise and refer based on NICE criteria
Review comorbidities and holistic care needs

Dr Rajesh Varmaobesity guidelines, obesity management, obesity treatment