Write a short note on obesity, metabolic syndrome and obesity hypoventilation syndrome.

Obesity — Definition

Obesity is abnormal or excessive fat accumulation presenting a risk to health. Body mass index (weight in kg divided by height in m²) is the standard measure, but Asian Indians develop metabolic risk at lower BMI, with greater visceral fat and insulin resistance for a given weight — the "thin-fat" Indian phenotype.

Waist circumference and waist-hip ratio predict cardiometabolic risk better than BMI, because visceral adipose tissue is metabolically active and drives insulin resistance.

Aetiology

Fundamentally a chronic positive energy balance, arising from an interaction of:

• Lifestyle: energy-dense diets, refined carbohydrate and sugar-sweetened beverages, sedentary work and screen time, urbanisation, disturbed sleep.
• Genetic: polygenic susceptibility; rare monogenic causes (leptin and MC4R deficiency, Prader–Willi and Bardet–Biedl syndromes).
• Endocrine (uncommon but must be excluded): hypothyroidism, Cushing's syndrome, PCOS, hypothalamic damage, growth hormone deficiency.
• Drugs: corticosteroids, antipsychotics (olanzapine, clozapine), sulphonylureas, insulin, pioglitazone, some antidepressants and antiepileptics, beta-blockers.
• Psychological: stress, depression, binge eating, and socioeconomic factors.

Metabolic Syndrome

A clustering of cardiometabolic risk factors centred on insulin resistance and central obesity, conferring roughly a doubled risk of cardiovascular disease and a fivefold risk of type 2 diabetes.

Diagnosis (harmonised criteria) — any 3 of 5:

1. Central obesity — waist circumference above the population- and sex-specific cut-off (≥ 90 cm men, ≥ 80 cm women for South Asians)

2. Triglycerides ≥ 150 mg/dL (or on treatment)

3. HDL cholesterol < 40 mg/dL in men, < 50 mg/dL in women (or on treatment)

4. Blood pressure ≥ 130/85 mmHg (or on treatment)

5. Fasting glucose ≥ 100 mg/dL (or known type 2 diabetes)

Pathophysiology: visceral adipose tissue releases free fatty acids and pro-inflammatory adipokines (TNF-α, IL-6, resistin) while reducing adiponectin, producing insulin resistance, hepatic steatosis, atherogenic dyslipidaemia (small dense LDL, low HDL, high triglycerides), endothelial dysfunction and a prothrombotic, pro-inflammatory state.

Complications of Obesity

Obesity Hypoventilation Syndrome (pickwickian Syndrome)

Definition — a triad: obesity (BMI ≥ 30), daytime hypercapnia (PaCO2 > 45 mmHg) while awake, and sleep-disordered breathing, after exclusion of other causes of hypoventilation.

Pathophysiology:

• the mechanical load of chest wall and abdominal fat reduces compliance and functional residual capacity and increases the work of breathing
• this combines with a blunted central respiratory drive and, in most patients, coexisting obstructive sleep apnoea, producing chronic CO2 retention with compensatory metabolic alkalosis (raised bicarbonate).

Features: daytime somnolence, morning headache, loud snoring with witnessed apnoeas, poor concentration, cyanosis, polycythaemia, and eventually pulmonary hypertension and right heart failure (cor pulmonale) with peripheral oedema.

Investigations:

• arterial blood gas showing hypercapnia with a raised bicarbonate — a raised serum bicarbonate in an obese, sleepy patient is a useful screening clue
• polysomnography
• pulmonary function tests (restrictive pattern)
• echocardiography for pulmonary hypertension
• thyroid function to exclude hypothyroidism.

Management:

• non-invasive positive pressure ventilation (NIV/BiPAP) is the mainstay, with CPAP where obstructive sleep apnoea predominates
• weight reduction, including bariatric surgery, is the only definitive treatment
• supplemental oxygen only with ventilatory support, since oxygen alone worsens hypercapnia
• avoid sedatives and opioids
• treat cor pulmonale.

Management of Obesity

• Lifestyle — the foundation: individualised calorie deficit with a culturally appropriate diet, reduced refined carbohydrate and sugar-sweetened drinks, portion control; at least 150–300 minutes of moderate activity weekly with resistance training; behavioural therapy, self-monitoring and realistic goals. A 5–10% weight loss produces clinically meaningful improvement in glycaemia, blood pressure and lipids.
• Treat secondary causes and review obesogenic drugs.
• Pharmacotherapy (adjunct to lifestyle, for BMI ≥ 30, or ≥ 27 with comorbidity): GLP-1 receptor agonists — liraglutide, semaglutide (substantial weight loss); tirzepatide (dual GIP/GLP-1); orlistat; naltrexone-bupropion.
• Bariatric (metabolic) surgery — sleeve gastrectomy, Roux-en-Y gastric bypass — for BMI ≥ 40, or ≥ 35 with significant comorbidity (thresholds are lower for Asian Indians: ≥ 37.5, or ≥ 32.5 with comorbidity). It produces the greatest and most durable weight loss and frequently remission of type 2 diabetes. Requires lifelong micronutrient supplementation and monitoring for vitamin B12, iron, calcium, vitamin D and thiamine deficiency.
• Screen for and manage complications — glucose, lipids, blood pressure, liver, sleep study where indicated.