GC064 I Am Overweight, Doctor
A clinical consultation addressing a patient's concern about excess body weight, involving assessment of BMI, identification of contributing factors, and discussion of lifestyle modifications and management strategies to achieve a healthier weight.
I Am Overweight, Doctor — Obesity & Hyperlipidaemia
This lecture is a core General Clerkship session covering obesity from definition and measurement all the way through aetiology, complications, and management (lifestyle, pharmacology, surgery). It is highly examinable because obesity intersects with virtually every system: cardiovascular, endocrine, respiratory, orthopaedic, surgical, psychiatric, and obstetric. The examiners love asking about:
- BMI thresholds for Asians vs Caucasians (a classic MCQ discriminator).
- Waist circumference cut-offs (ethnic-specific).
- Secondary causes of obesity and medications causing weight gain (commonly tested lists).
- Pharmacotherapy — mechanism, side effects, and which drugs have been withdrawn.
- Bariatric surgery indications and types (SAQ/minicase territory).
- Complications of obesity (systems-based list).
The lecture also touches on leptin physiology and the concept of adipose tissue as an endocrine organ — tested in SAQs that ask "why is sustained weight loss difficult?"
1. Measurements to Quantify Obesity
"BMI does not provide any indication of the distribution of fat." [1]
BMI = weight (kg) / height (m)² [1]
- A simple, widely used screening tool.
- Critical limitation: BMI tells you total mass relative to height but says nothing about where fat is distributed. A muscular rugby player and a sedentary person can share the same BMI with very different health risks.
High Yield — Asian BMI Cut-Offs
WHO Expert Consultation 2004: Caucasian-based BMI cut-off values are NOT directly applicable to other ethnic groups. [1]
Asian populations carry more visceral fat at any given BMI compared to Caucasians, meaning metabolic risk starts at a lower BMI. This is the reason for lower cut-offs.
| Classification | Caucasian (WHO 1998) | Asian (WHO 2004 / IOTF) | Risk |
|---|---|---|---|
| Underweight | < 18.5 | < 18.5 | Low (but ↑ other problems) |
| Normal / Acceptable | 18.5–24.9 | 18.5–22.9 | Average |
| Overweight / Increased risk | 25–29.9 | 23–24.9 | Increased |
| Obese Class I | 30–34.9 | 25–29.9 | Moderate |
| Obese Class II | 35–39.9 | ≥ 30 | Severe |
| Obese Class III | ≥ 40 | — | Very severe |
Exam Trap
If a stem says "A 45-year-old Chinese man, BMI 24 kg/m²" — he is already overweight by Asian standards. Don't apply Caucasian cut-offs in HKU exams unless the question specifies a Caucasian patient. Past papers have tested this distinction (e.g. 2022 Fourth Summative MCQ Q9 mentions BMI 27 with Cushing features — note how 27 falls into "Obese Class I" for Asians). [3]
"Increasingly used as a measure of central obesity. Ethnic differences recognised (IDF 2005)." [1]
| Population | Men | Women |
|---|---|---|
| Europids | ≥ 94 cm | ≥ 80 cm |
| Chinese | ≥ 90 cm | ≥ 80 cm |
Why WC matters more than BMI alone: Adipose tissue in a truncal distribution (around and in the abdomen) has a particularly strong relationship with the adverse metabolic and vascular effects of obesity [1]. Visceral fat is metabolically active — it secretes pro-inflammatory cytokines, contributes to insulin resistance, and drives atherogenesis in a way that subcutaneous gluteo-femoral fat does not.
WHO: WHR ≥ 0.9 in men, WHR ≥ 0.85 in women [1]
WHR is an older measure that captures the "apple vs pear" body shape concept. It supplements WC but in modern practice WC alone is more commonly used clinically.
- Skin-fold thickness — calipers measure subcutaneous fat at standardised sites. Research tool, not practical in clinic.
- Estimates of total body fat — DEXA, bioelectrical impedance, underwater weighing. Gold-standard but impractical for routine care. [1]
"Among persons aged 15–84 by BMI: 30% obese, 20% overweight." [1]
| Parameter | Male | Female |
|---|---|---|
| Obese (BMI ≥ 25 Asian) | 36% | 24% |
| Overweight (BMI 23–24.9 Asian) | 21% | 19% |
| Central obesity by WC | 28% | 37% |
Key epidemiological observations from the lecture:
- Proportion classified as overweight/obese decreased with increasing household income — inverse socioeconomic gradient, consistent with international data. Lower-income groups have poorer access to healthy food and exercise facilities. [1]
- Prevalence of central obesity generally increases with age — as lean mass declines, hormonal changes (especially post-menopause) favour visceral fat deposition. [1]
This is a classic exam list. The lecture organises it by system, which is exactly how you should reproduce it in an SAQ.
| System | Conditions |
|---|---|
| Cardiovascular | Hypertension, Coronary heart disease, Stroke |
| Metabolic | Type 2 DM, Dyslipidaemia, Insulin resistance, PCOS |
| Gastrointestinal | Hiatus hernia, Gallstones, Colorectal cancer, Non-alcoholic hepatic steatosis (MASLD) |
| Respiratory | Breathlessness, Obstructive sleep apnoea, Hypoventilation (Obesity hypoventilation syndrome / Pickwickian) |
| Neurological | Nerve entrapment, Sciatica |
| Breast | Breast cancer, Gynaecomastia |
| Genitourinary | Stress incontinence, Reduced fertility (PCOS), Pregnancy complications |
| Orthopaedic | Osteoarthritis of weight-bearing joints |
| Psychological | Poor self-esteem, Depression |
Why these complications occur — from first principles:
- CV: Excess adiposity → ↑ circulating volume → ↑ cardiac output → ↑ BP. Also accelerated atherosclerosis from dyslipidaemia + chronic inflammation.
- T2DM / Insulin resistance: Visceral fat → ↑ free fatty acids → lipotoxicity to pancreatic β-cells + ↓ insulin sensitivity in muscle/liver.
- OSA: Fat deposition around pharynx → airway collapse during sleep → intermittent hypoxia → daytime somnolence, pulmonary hypertension, arrhythmias. [4]
- Gallstones: Obesity → ↑ cholesterol secretion into bile → supersaturation → cholesterol stones. The "4 Fs" mnemonic: Fat, Female, Forty, Fertile. [5]
- MASLD: Insulin resistance → ↑ hepatic de novo lipogenesis + impaired VLDL export → hepatic steatosis → potential progression to steatohepatitis → cirrhosis. [6]
- OA: Mechanical overload on weight-bearing joints + adipokine-mediated low-grade inflammation.
- Breast cancer: Adipose tissue aromatises androgens to oestrogens (especially post-menopause) → oestrogen-driven tumour growth.
"Risk of CHD doubled if BMI > 25 and quadrupled if BMI ≥ 29." [1]
High Yield
"As weight reduction can alleviate obesity-associated co-morbidities, the goal of obesity treatment should be in the reduction of co-morbidity rather than for cosmetic reasons." [1]
This is a commonly tested concept — the examiner wants you to frame management in terms of health benefit, not appearance.
4. Aetiology of Obesity
"Mismatch between energy intake and energy expenditure." [1]
This is thermodynamics: if calories in > calories out, excess energy is stored as fat. But it is oversimplistic to tell patients to "just eat less" — the regulation of energy balance is a tightly controlled neuro-hormonal system.
- Only very few cases of obesity solely due to single-gene defect (e.g. leptin deficiency, MC4R mutations — extremely rare in humans). [1]
- Genetic influences are generally polygenic. [1]
- Adoption studies and complex segregation analysis suggest heritability of about 33%. [1]
- This means ~one-third of inter-individual variation in BMI can be attributed to genetics, but the remaining two-thirds is environmental/behavioural.
"Obesity is associated with food intake and content of fat in diet; sedentary lifestyle; inverse relationship between socio-economic status and the prevalence of obesity." [1]
- Calorie-dense, high-fat foods are cheap and accessible.
- Modern lifestyles promote sitting (desk jobs, screen time, driving).
- Lower SES → less access to healthy food, safe exercise spaces, and health literacy.
These are the conditions where obesity is a consequence of another disease. Always consider these in your differential, especially if weight gain is rapid, recent-onset, or accompanied by other endocrine features.
Conditions associated with obesity: [1]
- Hypothyroidism
- Cushing's syndrome
- Hypothalamic tumours (e.g. craniopharyngioma → disrupts satiety centre)
- Growth hormone deficiency
- Hypogonadism in males — associated with increase in abdominal and visceral fat
- Polycystic ovary syndrome
Exam Approach — Cushing's vs Simple Obesity
A 2022 MCQ (Q9) tests this distinction: woman with oligomenorrhoea, weight gain, moon facies, proximal weakness, thin skin, purplish striae, and BMI 27 → answer is Cushing syndrome, not simple obesity or PCOS. The discriminator is the catabolic signs (thin skin, proximal myopathy, striae) that you do NOT see in simple obesity. Simple obesity actually causes thickening of skin, and striae are typically pink/white, not purple. [3]
Common medications causing weight gain: [1]
| Drug Class | Examples |
|---|---|
| Antidepressants | MAOIs, TCAs (nortriptyline, amitriptyline, doxepin), paroxetine, citalopram, escitalopram, imipramine, mirtazapine |
| Antipsychotics | Thioridazine, olanzapine, risperidone, clozapine, quetiapine |
| Diabetes medications | Insulin, sulfonylureas, thiazolidinediones (TZDs), meglitinides |
| Glucocorticoids | Prednisone |
| Anticonvulsants | Valproate, carbamazepine |
Why these cause weight gain:
- Olanzapine/clozapine: potent H1 antihistamine + 5-HT2C blockade → ↑ appetite centrally. Among antipsychotics, olanzapine and clozapine cause the most weight gain.
- Insulin/SU/TZDs: promote anabolism; insulin promotes lipogenesis and inhibits lipolysis; TZDs cause adipocyte differentiation (paradoxically improving insulin sensitivity by expanding subcutaneous fat capacity but causing weight gain).
- Steroids: cortisol → ↑ gluconeogenesis, ↑ appetite, redistribution of fat to truncal/visceral compartments.
- Valproate: mechanism unclear but likely involves ↑ appetite + effects on fatty acid metabolism.
- Mirtazapine: H1 + 5-HT2C blockade → significant appetite stimulation.
Important Clinical Pearl
When a patient presents with weight gain, always review their medication list. Switching from olanzapine to aripiprazole, or from a sulfonylurea to an SGLT2 inhibitor/GLP-1 RA, can significantly help. Drug-induced weight gain is a modifiable factor.
5. Regulation of Energy Balance — Leptin & Adipose Tissue Physiology
"Hypothalamus — a centre for regulation of energy balance. Integrates neural, hormonal and nutrient messages from the body and sends signals to higher centres leading to feeling of hunger or satiety. Controls energy expenditure via autonomic nervous system and pituitary hormones." [1]
The hypothalamus contains two key nuclei:
- Arcuate nucleus: contains POMC/CART neurons (anorexigenic — suppress appetite) and NPY/AgRP neurons (orexigenic — stimulate appetite).
- These receive input from leptin, ghrelin, insulin, GLP-1, PYY, and nutrient signals (glucose, fatty acids, amino acids).
"Peptide hormone synthesised by adipocytes. Acts in the hypothalamus to suppress food intake and increase energy expenditure." [1]
Key lecture points on leptin:
- Mutation in leptin gene → ob/ob mice; Mutation in leptin receptor gene → db/db mice, fa/fa rat. [1]
- Mutations in leptin or leptin receptor as a cause of obesity are extremely rare in humans. [1]
- Leptin levels rise in parallel with fat mass. [1]
- Leptin concentration is increased in obese subjects. [1]
- Human obesity is NOT a state of leptin deficiency or of extreme leptin insensitivity → ? Partial resistance. [1]
Why this matters: This explains why simply giving leptin to obese patients doesn't work (unlike the rare leptin-deficient individual). Obese humans have HIGH leptin but the hypothalamus is relatively resistant to its signal — a concept analogous to insulin resistance in T2DM. The system preferentially defends against weight LOSS (evolutionary advantage in times of famine) rather than weight GAIN.
"Adipose tissue is NOT an inert tissue. It is a major endocrine and secretory organ. Releases a wide range of protein factors and signals termed adipokines (e.g. adiponectin), in addition to fatty acids and other lipid moieties." [1]
Adipokines include:
- Leptin — satiety signal (see above)
- Adiponectin — insulin-sensitising, anti-inflammatory, anti-atherogenic. Levels are decreased in obesity (paradoxically, the one beneficial adipokine goes down).
- TNF-α, IL-6 — pro-inflammatory cytokines. Levels are increased in obesity → chronic low-grade inflammation → insulin resistance, endothelial dysfunction.
- Resistin — promotes insulin resistance.
- PAI-1 — promotes thrombosis.
"Long-term signals of energy stores and short-term fluctuations in food intake are released from adipose tissues and the gut endocrine system. These signals are integrated in the hypothalamus and brainstem and modulate neuropeptide release, resulting in subsequent changes in appetite, behaviour and energy expenditure to maintain a stable weight." [1]
"Physiological adaptations (e.g. increase in appetite-stimulating hormones like ghrelin and decrease in appetite-suppressing hormones) to defend against weight loss." [1]
In plain English: When you lose weight, your body fights back:
- Ghrelin (the "hunger hormone" from the stomach) goes UP.
- Leptin, PYY, GLP-1 go DOWN.
- Basal metabolic rate decreases (adaptive thermogenesis).
- The net effect: you feel hungrier, you burn fewer calories, and your body physiologically drives you back towards your previous weight set-point.
This is why diet-only approaches have a ~95% recidivism rate at 5 years, and why pharmacotherapy and surgery are sometimes necessary.
7. Management of Obesity
Management aims: [1]
- Weight reduction
- Maintenance of weight loss
- Modification of concurrent risk factors for mortality and morbidity such as smoking, diabetes, hypertension and hyperlipidaemia
- BE REALISTIC. Treatment directed towards health rather than cosmetic goals
- Weight loss of 5–10% of total body weight is already associated with health benefit
High Yield — The 5–10% Rule
Even a modest 5–10% weight loss improves: BP (↓ ~5 mmHg systolic), HbA1c (↓ 0.5–1%), lipid profile (↓ TG, ↑ HDL), liver enzymes in MASLD, sleep apnoea severity, and joint pain. This is a commonly tested concept — the question will ask "what percentage of weight loss is clinically beneficial?" Answer: 5–10%. [1]
Strategies for weight reduction: [1]
- Set a realistic goal
- Lifestyle modification — diet and exercise
- Drug therapy
- Surgery
"Cornerstone of any treatment program for obesity." [1]
| Diet Type | Definition | Key Points |
|---|---|---|
| LCD (Low-Calorie Diet) | ≥ 800 kcal/d, typically 800–1500 kcal/d | Standard approach |
| VLCD (Very Low-Calorie Diet) | < 800 kcal/d | Faster initial weight loss but NOT superior for maintenance at 1 year. Should only be used under medical supervision. |
Key facts:
- Weight loss of around 0.5 kg/week is optimal (600 kcal/day deficit). [1]
- Faster rates of weight loss will lose not only fat but lean body mass — this is harmful because lean mass (muscle) is metabolically active and its loss further reduces BMR, making regain easier. [1]
- VLCD leads to faster rate in weight reduction in first 2–3 months but NOT superior in maintenance of weight loss after 1 year. [1]
- Long-term weight loss in most trials (FU 2–7 years): weight loss in the range of 2 to 6 kg — this is sobering and underscores why diet alone is insufficient for severe obesity. [1]
- Diet therapy effective in promoting significant weight loss (max 4–7%). [1]
- Low carbohydrate diets are somewhat more effective in the short term (3–6 months). [1]
- All diets appear equivalent over the long term (1 year or longer). [1]
Clinical implication: The "best" diet is the one the patient can adhere to long-term. Whether it's low-carb, low-fat, Mediterranean, or DASH — compliance matters more than macronutrient composition.
For diabetic patients specifically: 30 kcal/kg ideal body weight per day, 40–50% carbohydrates (may be less for overweight patients), 30% fat (< 7% saturated), 20–30% protein, fibre 20–35 g/day. [7]
"Combining dietary modification with adequate physical activity has been repeatedly shown to be important for initial weight loss and NECESSARY for long-term weight maintenance." [1]
"Gradual increase physical activity until energy expenditure of 1000 to 1500 kcal/week." [1]
Why exercise is essential for maintenance: Exercise prevents the decline in basal metabolic rate that accompanies caloric restriction. It also improves insulin sensitivity, lipid profile, and mental health independently of weight loss.
1000–1500 kcal/week translates roughly to 150–300 minutes of moderate-intensity aerobic activity per week (e.g. brisk walking ~30–60 min/day most days).
7.5 Drug Therapy
"Only appropriate in individuals who are at medical risk from their level of obesity and have not responded to more traditional, conservative management." [1]
Indications: BMI > 30, OR BMI 27–29 with comorbidities. [1]
"Treatment should be discontinued if patient does not get medical benefit." [1]
| Agent | Mechanism | Mean Weight Loss | Side Effects | Status |
|---|---|---|---|---|
| Orlistat | GI lipase inhibitor → ↓ dietary fat absorption by 30% | 2.9–3.4 kg (2.9–3.4%) | GI upset, steatorrhoea, ↓ absorption of fat-soluble vitamins (ADEK) | Available |
| Phentermine/Topiramate (Qsymia) | Norepinephrine-releasing + GABA modulator | 6.6 kg (6.6%) at recommended dose; 8.6 kg (8.6%) at high dose | Teratogenicity, ↑ HR, psychiatric/cognitive effects, metabolic acidosis | FDA 2012; not yet available in HK |
| Bupropion/Naltrexone (Contrave) | Dopamine/NE reuptake inhibitor + opioid antagonist | 4.8% | Nausea, constipation, headache; monitor for suicidal thoughts | FDA 2014 |
| Liraglutide (Saxenda) | GLP-1 receptor agonist | 5.8 kg (5.4%) | Mainly GI (nausea, vomiting) | FDA 2014; 3 mg/day SC |
| Semaglutide (Wegovy) | GLP-1 analogue (94% homology to human GLP-1), half-life ~1 week | ~15% | Mainly GI | FDA June 2021; 2.4 mg weekly SC |
| Drug | Mechanism | Reason for Withdrawal | Year |
|---|---|---|---|
| Rimonabant | Endocannabinoid receptor (CB1) antagonist | Psychiatric side effects (depression, suicidality) | 2008 |
| Sibutramine | Serotonergic agent (SNRI) | ↑ CV events (MI, stroke) — SCOUT trial | 2010 |
| Lorcaserin | Selective 5-HT2C receptor agonist | ↑ Cancer risk | 2020 |
Orlistat:
"A gastrointestinal lipase inhibitor. Promotes weight loss by inhibiting gastrointestinal lipase and thus lowering absorption of dietary fat. Decreases dietary fat absorption by 30% with a dose of 120 mg three times a day. Systemic absorption is negligible. Possible side effects: GI upset, steatorrhoea, decreased absorption of fat-soluble vitamins." [1]
- Why steatorrhoea: Unabsorbed fat passes through → oily/fatty stools, flatulence, faecal urgency. This actually serves as a behavioural reinforcement — if patients eat a high-fat meal, the GI symptoms are worse, encouraging low-fat eating.
- Clinical pearl: Supplement fat-soluble vitamins (A, D, E, K) separately, taken 2 hours apart from orlistat.
Liraglutide (Saxenda):
"GLP-1 receptor agonist. Enhances glucose-stimulated insulin secretion and reduces glucagon secretion, delays gastric emptying and increases satiety by central effects on the hypothalamus. A higher dose formulation developed specifically for the treatment of obesity (3 mg/day, subcutaneous injection)." [1]
- Why SC injection: GLP-1 analogues are peptides — they would be degraded if taken orally (though oral semaglutide exists for DM, the obesity dose requires SC).
- Dual benefit: If the patient also has T2DM, a GLP-1 RA treats both conditions simultaneously.
Semaglutide (Wegovy):
"GLP-1 analogue, 94% homology to human GLP-1. Half-life approximately 1 week → can be given as a weekly injection. Approved for Type 2 DM at 1 mg weekly. High dose of 2.4 mg weekly approved by FDA for treatment of obesity in June 2021. Mean weight loss approximately 15%. Side effects: mainly gastrointestinal." [1]
- Why ~15% weight loss: This is a game-changer compared to older agents. The STEP trials showed that semaglutide 2.4 mg weekly produces weight loss approaching that of some bariatric surgeries. Mechanism: potent central appetite suppression + delayed gastric emptying.
Phentermine/Topiramate (Qsymia):
"Phentermine — anorexigenic agent, acts via enhancement of norepinephrine release and possibly blockade of norepinephrine reuptake. Topiramate — neurostabiliser for seizures and migraine prophylaxis, exact mechanism for weight loss not known. Amount of weight loss achieved with combination > either agent alone." [1] "Adverse events: teratogenicity, slight increase in heart rate, psychiatric and cognitive adverse effects, metabolic acidosis." [1]
- Teratogenicity: Topiramate is associated with oral cleft defects → REMS program mandates pregnancy testing and contraception. Not available in HK.
Bupropion/Naltrexone (Contrave):
"Bupropion (inhibitor of neuronal reuptake of dopamine and norepinephrine) — also used as antidepressant and smoking cessation aid. Naltrexone (opioid antagonist) — also used for alcohol/opioid dependence. Reduces appetite and food cravings." [1] "Side effects: nausea, constipation, headache, vomiting, dizziness, insomnia, dry mouth, diarrhoea. Monitor for mood changes, suicidal thoughts or actions." [1]
- Why the combination works: Bupropion stimulates POMC neurons → releases α-MSH (appetite suppression). But POMC neurons also release β-endorphin, which feeds back to inhibit further POMC firing. Naltrexone blocks this opioid auto-inhibition → sustained POMC activation → sustained appetite suppression.
7.6 Bariatric Surgery
"Patients considered eligible for surgery if: [1]
- BMI ≥ 40 kg/m² without comorbidity
- BMI ≥ 35 kg/m² with comorbidity (e.g. diabetes, respiratory insufficiency)"
Exam Note
These are Caucasian BMI thresholds commonly quoted in guidelines. For Asian patients, some centres use lower thresholds (e.g. BMI ≥ 37.5 without or ≥ 32.5 with comorbidities), but the lecture cites the standard cut-offs. Use the lecture values in exams.
"Reduce the size of reservoir/intake" and/or "Reduce the efficacy of absorption." [1]
| Procedure | Mechanism | Key Features |
|---|---|---|
| Bioenterics Intragastric Balloon | Non-surgical; placed endoscopically; acts as a bezoar to induce early satiety | Non-permanent, reversible; remove after 6–9 months. A kind of behavioural therapy. |
| Laparoscopic Adjustable Gastric Banding (AGB) | Restrictive: inflatable belt around upper stomach → limits intake | Least invasive bariatric surgery. Lower mortality/complications but higher reoperation rate and less weight loss than bypass. |
| Laparoscopic Sleeve Gastrectomy (LSG) | Restrictive: greater curve excised by staples → 150 cc banana-shaped pouch | No bypass/malabsorption. More effective than AGB, comparable to gastric bypass. |
| Roux-en-Y Gastric Bypass (RYGB) | Restrictive + Malabsorptive: small gastric pouch + Roux-en-Y anastomosis | Most effective for weight loss. More complications than AGB. |
Key lecture points on comparison: [1]
- AGB: lower mortality and complication rates BUT higher reoperation rate and less substantial weight loss than GB.
- Gastric bypass: more effective in weight loss but associated with more complications.
- Sleeve gastrectomy: more effective in weight loss than AGB and comparable to GB.
"Mean 20-year weight reduction in the large Swedish Obese Subjects' study was 25% for Roux-en-Y gastric bypass and 15% for adjustable gastric banding." [1]
"An effective means to achieving lasting weight loss and improving metabolic disease and reducing cardiovascular risk in selected candidates." [1]
"Pre-op multi-disciplinary assessment is needed to select the appropriate candidates." [1]
"Choice of surgical modality should take individual goals and existing comorbidities into account." [1]
"Long-term follow-up is mandatory to support a safe outcome." [1]
Adverse intraoperative events ~5% (10 clinical sites in US). [1]
Long-term complications include:
- Nutritional deficiencies (especially after RYGB): iron, B12, folate, calcium, vitamin D, fat-soluble vitamins — due to bypassed duodenum/proximal jejunum where these are absorbed.
- Dumping syndrome (after RYGB): rapid gastric emptying → osmotic fluid shifts → nausea, cramping, diarrhoea, vasomotor symptoms.
- Anastomotic leak/stricture.
- Internal hernias (after RYGB).
- Gallstone formation (rapid weight loss → ↑ cholesterol saturation of bile).
- Band slippage/erosion (AGB-specific).
- GORD can worsen after sleeve gastrectomy.
The NCEP ATP III (2005) definition of metabolic syndrome is frequently tested alongside obesity: [2]
≥ 3 out of 5 criteria:
| Criterion | Threshold |
|---|---|
| Central obesity (WC) | > 102 cm (M) / > 88 cm (F) [Caucasian]; or ethnic-specific |
| Fasting glucose | ≥ 5.5 mmol/L or on treatment |
| Triglycerides | > 1.7 mmol/L |
| HDL-C | < 1.034 mmol/L (M) / < 1.293 mmol/L (F) or on treatment |
| Blood pressure | > 130 SBP or > 85 DBP or on treatment |
- OSA (GC 024): Obesity is the most important modifiable risk factor for OSA. A BMI 24 with normal sleep quality but fatigue/snoring → look for non-sleep-related causes first (see 2024 MCQ Q39). [4][8]
- CKD (GC 034): Obesity is a CKD risk factor → recommend eGFR testing in overweight/obese patients. [9]
- Gallstones: "Fat, Female, Forty, Fertile" — 2021 MCQ Q81 tests gallstone imaging in obese female. [5][10]
- MASLD (GC 240): Obesity → insulin resistance → hepatic steatosis. [6]
- Cushing's syndrome: The exam loves asking you to differentiate Cushing's from simple obesity. Key discriminators: thin skin, proximal myopathy, purple striae, easy bruising (catabolic features) are present in Cushing's but NOT in simple obesity. [3]
- VTE in pregnancy: Maternal obesity is a risk factor for venous thromboembolism → LMWH prophylaxis considerations (2025 MCQ Q10). [11]
- Familial hypercholesterolaemia: While not "obesity" per se, hyperlipidaemia management overlaps. Dutch criteria for FH diagnosis are important. [12]
10. Clinical Approach Summary
- Duration and trajectory of weight gain
- Diet and exercise habits (24-hour dietary recall)
- Psychiatric history: depression, binge eating disorder
- Medication review (drug-induced weight gain)
- Symptoms of secondary causes: fatigue/cold intolerance (hypothyroidism), striae/weakness (Cushing's), menstrual irregularity (PCOS), headache/visual field defects (hypothalamic tumour)
- Screen for complications: chest pain, dyspnoea, snoring, daytime sleepiness, polyuria/polydipsia, joint pain
- Family history of obesity, DM, CVD
- Psychosocial: self-esteem, motivation for change, socioeconomic factors
- Vitals: BP (HTN), HR
- Anthropometry: Weight, height, BMI, waist circumference
- Endocrine stigmata: Moon face, buffalo hump, striae (Cushing's); thyroid enlargement; acanthosis nigricans (insulin resistance); hirsutism/acne (PCOS)
- Cardiovascular: Signs of heart failure
- Respiratory: Mallampati score (OSA risk)
- Abdominal: Hepatomegaly (MASLD), hernias
- Skin: Acanthosis nigricans, intertrigo, skin tags
- MSK: Joint tenderness (OA)
- Bloods: FPG/HbA1c, lipid profile (TC, LDL, HDL, TG), LFTs (MASLD screen), TFTs, cortisol (if Cushing's suspected), renal function
- Urine: Urinary free cortisol (if Cushing's suspected), uACR
- Sleep study: If symptoms suggest OSA
- Imaging: US abdomen (fatty liver, gallstones), DEXA if considering body composition assessment
11. Likely Exam Questions
-
"A 45-year-old Chinese woman, BMI 24.5 kg/m². What is her classification?" → Overweight (Asian cut-off: 23–24.9). Trap: if you use Caucasian cut-offs, you'd say "normal."
-
"Which of the following medications is LEAST likely to cause weight gain: (A) Olanzapine (B) Metformin (C) Valproate (D) Insulin?" → (B) Metformin — it is weight-neutral to weight-reducing.
-
"A patient on orlistat complains of fatty stools. What vitamin deficiency should you screen for?" → Fat-soluble vitamins: A, D, E, K.
-
"Which anti-obesity drug was withdrawn due to increased cardiovascular events?" → Sibutramine (2010).
-
"BMI threshold for bariatric surgery in a patient WITH comorbidities?" → ≥ 35 kg/m².
-
"List 6 diseases/complications attributable to obesity, organised by system." — Use the lecture table.
-
"Name 4 endocrine conditions associated with obesity." — Hypothyroidism, Cushing's, PCOS, hypogonadism in males, GH deficiency, hypothalamic tumour.
-
"Describe the mechanism of action and major side effect of semaglutide in obesity treatment." — GLP-1 RA → ↑ satiety via hypothalamus, delayed gastric emptying, ↑ glucose-stimulated insulin secretion; SE: mainly GI (nausea, vomiting).
-
"What percentage of weight loss is associated with health benefit? What are realistic long-term weight loss outcomes with diet therapy?" → 5–10%; 2–6 kg over 2–7 years.
-
"Compare sleeve gastrectomy and Roux-en-Y gastric bypass." — See surgical comparison table.
Active Recall - I Am Overweight, Doctor
High Yield Summary
- Asian BMI cut-offs are lower than Caucasian: Overweight ≥ 23, Obese ≥ 25 for Asians vs ≥ 25 and ≥ 30 for Caucasians.
- Waist circumference for Chinese: Men ≥ 90 cm, Women ≥ 80 cm — central obesity has the strongest link to metabolic complications.
- Complications span all systems: CV (HTN, IHD, stroke), Metabolic (T2DM, dyslipidaemia), GI (MASLD, gallstones, CRC), Respiratory (OSA), MSK (OA), Psychological (depression).
- Always exclude secondary causes: Hypothyroidism, Cushing's, PCOS, hypothalamic tumours, drug-induced weight gain.
- Management pyramid: Lifestyle (diet + exercise) → Pharmacotherapy (if BMI > 30 or > 27 with comorbidities) → Surgery (BMI ≥ 40 or ≥ 35 with comorbidities).
- 5–10% weight loss is already beneficial — be realistic, aim for health, not cosmesis.
- Semaglutide (Wegovy) is the most effective pharmacotherapy (~15% weight loss), given as weekly SC injection.
- Three withdrawn drugs: Rimonabant (psych), Sibutramine (CV), Lorcaserin (cancer) — know them.
- Bariatric surgery: Sleeve gastrectomy offers a good balance of efficacy and safety. RYGB most effective but most complications. Long-term follow-up is mandatory.
- Sustained weight loss is hard because of physiological counter-regulation (↑ ghrelin, ↓ leptin, ↓ BMR) — this is testable knowledge.
[1] Lecture slides: GC 064. I am overweight, doctor.pdf (all pages) [2] Senior notes: Ryan Ho Endocrine.pdf (p.116 — BMI classification table, metabolic syndrome definition) [3] Past papers: 2022 Fourth Summative MCQ.pdf (Q9 — Cushing syndrome vs obesity) [4] Past papers: 2024 Fourth Summative MCQ.pdf (Q39 — fatigue/sleepiness in normal-BMI patient, OSA vs non-sleep causes) [5] Senior notes: Block A - Upper abdominal pain_ peptic ulcer; pancreatitis and gallstone.pdf (p.26 — gallstone risk factors including obesity) [6] Lecture slides: GC 240. MASLD and Alcoholic Liver Disease.pdf (MASLD link to obesity) [7] Senior notes: Block A - Deterioration of eyesight in a diabetic patient_ diabetic complications.pdf (p.12 — dietary management in DM) [8] Lecture slides: GC 024. A Fatigued and Sleepy Patient.pdf [9] Senior notes: Block A - Chronic Kidney Disease and its Complications.pdf (p.10 — obesity as CKD risk factor) [10] Past papers: 2021 Fourth Summative Assessment MCQ.pdf (Q81 — gallstones in obese female) [11] Senior notes: Block A - Leg swelling and chest pain_ deep vein thrombosis; pulmonary embolism; Thrombophilia.pdf (p.19 — maternal obesity as VTE risk factor) [12] Senior notes: Introduction to Clinical pharmacology (I) (Pharmaco- Genomics, Precision Medicine).pdf (p.2 — FH, Dutch criteria)
GC063 I Am Losing Weight And Sweating All The Time
A clinical presentation characterized by unintentional weight loss and excessive sweating, commonly suggesting hyperthyroidism, malignancy, chronic infection, or other hypermetabolic or systemic conditions requiring urgent evaluation.
GC065 I Have An Itchy Rash
A clinical presentation of pruritic dermatitis requiring systematic evaluation to distinguish among common causes such as eczema, contact dermatitis, urticaria, fungal infections, and scabies.