Obesitas Dewasa

01Pathophysiology

Obesity is a chronic metabolic disease characterized by excessive fat mass accumulation that increases the risk of numerous non-communicable diseases and reduces life expectancy. The fundamental mechanism revolves around a sustained positive energy balance where caloric intake exceeds energy expenditure over prolonged periods.

The critical pathophysiological driver is visceral adipocyte hypertrophy and hyperplasia. As visceral fat depots expand, adipocytes become dysfunctional and shift toward a pro-inflammatory secretory profile. These cells release increased amounts of TNF-alpha, IL-6, and other adipokines while simultaneously reducing adiponectin output. This creates a state of chronic low-grade systemic inflammation that damages vascular endothelium, promotes insulin resistance, and accelerates atherogenesis. This is why obesity is tightly linked to hypertension, type 2 diabetes, dyslipidemia, and coronary artery disease as a cluster rather than isolated conditions.

Insulin resistance is another central mechanism. Excess free fatty acids from enlarged visceral adipocytes impair insulin signaling in skeletal muscle and liver. The pancreas compensates with hyperinsulinemia, which further promotes lipogenesis and sodium retention (contributing to hypertension). Over time, beta-cell exhaustion leads to overt type 2 diabetes. This explains why the metabolic syndrome criteria (waist circumference, triglycerides, HDL, blood pressure, fasting glucose) are all downstream consequences of visceral adiposity.

From a mechanical standpoint, excess body weight places disproportionate stress on weight-bearing joints (particularly the knees), the lumbar spine, and the plantar fascia. This is why osteoarthritis, low back pain, and plantar fasciitis are common musculoskeletal comorbidities. Excess pharyngeal and neck soft tissue contributes to upper airway collapse during sleep, producing obstructive sleep apnea (OSA).

In critically ill patients, obesity increases ICU mortality by 2.52-fold (95% CI 1.3-4.9), prolongs ventilator duration, and raises the risk of surgical site infection by 4.42-fold, ARDS by 1.8-fold, and acute kidney injury by 3.07-fold. These outcomes reflect impaired respiratory mechanics, heightened inflammatory responses, and increased technical difficulty of procedures.

02Classification and Clinical Manifestation

BMI Classification (Asia-Pacific Criteria)

Waist Circumference Cutoffs (Asia-Pacific Consensus)

Body Fat Percentage (General Threshold for Obesity)

Edmonton Obesity Staging System (EOSS)

This staging system is central to clinical decision-making because it goes beyond BMI alone and incorporates the presence and severity of comorbidities, psychological status, and functional limitations. A patient with BMI 27 but EOSS Stage 3 warrants more aggressive therapy than a patient with BMI 32 at EOSS Stage 0.

Metabolic Syndrome Criteria

Diagnosed when 3 of 5 criteria are met:

Sarcopenic Obesity Classification

Screened using the SARC-F questionnaire (score $\ge 4\backslash geq\; 4$ suggests possible sarcopenia), then confirmed by measuring muscle mass, strength, and function:

03Diagnostic Workup

The best initial step in diagnosis is anthropometry: calculating BMI and measuring waist circumference. For Asia-Pacific populations, obesity is defined as BMI $\ge 25{\text{kg/m}}^2\backslash geq\; 25\backslash \; \backslash text\{kg/m\}^2$ with waist circumference >90 cm (male) or >80 cm (female). This is lower than the WHO global cutoff of $\ge 30{\text{kg/m}}^2\backslash geq\; 30\backslash \; \backslash text\{kg/m\}^2$, a frequent source of confusion.

Once obesity is established, the priority shifts to screening for comorbidities rather than confirming the obesity itself. The routine workup includes a lipid profile, fasting glucose with OGTT and HbA1c, and an EKG. These are ordered to detect metabolic syndrome, prediabetes or type 2 DM, and baseline cardiac status. Liver enzymes are checked for hepatic steatosis. TSH is obtained to rule out hypothyroidism as a contributing or exacerbating factor.

Body composition analysis via bioimpedance analysis (BIA) provides additional value beyond BMI. It measures fat-free mass index (FFMI), which is essential for identifying sarcopenic obesity, a condition where fat mass replaces muscle mass. Normal FFMI cutoffs are $\ge 17{\text{kg/m}}^2\backslash geq\; 17\backslash \; \backslash text\{kg/m\}^2$ for males and $\ge 15{\text{kg/m}}^2\backslash geq\; 15\backslash \; \backslash text\{kg/m\}^2$ for females. BMI alone can miss sarcopenic obesity entirely because muscle loss is masked by fat gain.

For cardiovascular risk stratification in obese patients, stress echocardiography is the preferred noninvasive cardiac imaging modality because it has no weight limit, no radiation, and maintains diagnostic validity in obese patients. In contrast, standard EKG has low sensitivity and sensitivity for ischemia detection in this population, and CT/MRI-based methods face technical limitations from body habitus (image degradation, bore size, weight limits).

EOSS staging is then performed by integrating all clinical findings to classify the patient into Stage 0-4, which directly guides therapeutic intensity.

04Management and Treatment

Pharmacotherapy Summary

Bariatric Surgery Summary

Phase 1: Lifestyle Modification (All Patients)

This is the foundation for every obesity patient regardless of BMI or comorbidity status.

Nutritional therapy centers on caloric restriction. The most evidence-supported approach is reducing total daily energy intake by 500 kcal with fat restriction (<30% of total calories). Very low-calorie diets (<800 kcal/day) and low-calorie diets (800-1000 kcal/day) require medical supervision and may only be sustained for a maximum of 12 weeks. These approaches can produce 15-25% relative weight loss but carry risk of yo-yo rebound if not managed by experienced practitioners. A high-protein, low-carbohydrate diet achieves more weight loss in the first 6 months due to fluid loss and ketosis-induced appetite suppression, but must be used cautiously in patients with osteoporosis, renal disease, or elevated LDL. The Mediterranean diet reduces risk of coronary artery disease, cancer, and chronic inflammatory disease and emphasizes plant-based foods, whole grains, olive oil, and fish.

Physical activity should combine aerobic exercise ($\ge 5\backslash geq\; 5$ times/week, progressing from 150 to 300 minutes/week at moderate intensity), resistance training (2-3 times/week, 2-4 sets of 8-12 reps at 60-70% of 1-RM), and flexibility training ($\ge 2-3\backslash geq\; 2-3$ times/week). Before starting, patients should undergo EKG and spirometry. A realistic target is approximately 4 hours/week of exercise or roughly 2000 kcal/week of energy expenditure. Aerobic exercise at moderate to high intensity reduces visceral and ectopic fat (Level 1a, Grade A evidence) even without weight loss on the scale.

Behavioral therapy requires 12-24 structured sessions. Techniques include goal-setting, self-monitoring of intake and activity, stimulus control (limiting cues to eat), cognitive restructuring (addressing maladaptive thoughts about body image and weight), and motivational interviewing for ambivalent patients. Patients with binge eating disorder or comorbid depression require cognitive behavioral therapy with psychiatric referral.

Phase 2: Pharmacotherapy (Adjuvant)

Indicated for BMI $\ge 30\backslash geq\; 30$ or $\ge 25\backslash geq\; 25$ with at least one comorbidity, in addition to lifestyle modification. Drug therapy is never standalone.

Orlistat (3 x 120 mg daily) inhibits gastrointestinal lipase, reducing fat absorption by roughly 30%. It produces approximately 2.9 kg weight loss after one year. Side effects (steatorrhea, fecal urgency, oily spotting) diminish when fat intake is restricted. Safe for up to 4 years of use. Contraindicated in cholestasis and chronic malabsorption syndrome.

GLP-1 receptor agonists (liraglutide, semaglutide) and the dual GLP-1/GIP agonist (tirzepatide) work by enhancing satiety signaling, slowing gastric emptying, and improving insulin sensitivity. Semaglutide 2.4 mg/week has demonstrated safety up to 68 weeks. All three share the same contraindication profile: personal/family history of medullary thyroid carcinoma or MEN2, pancreatitis, gastroparesis, and pregnancy. The critical response checkpoint is 3 months: if $\ge 5\mathrm{\%}\backslash geq\; 5\backslash \%$ weight loss is not achieved, the patient is classified as a non-responder and must be switched to a different agent or escalated to bariatric intervention.

For patients with comorbid conditions, the algorithm guides drug selection. In patients with tachycardia or uncontrolled hypertension, phentermine/topiramate and naltrexone/bupropion are avoided. In patients with history of medullary thyroid cancer or pancreatitis, all GLP-1 agonists are contraindicated; naltrexone/bupropion, orlistat, and phentermine/topiramate remain options. For patients on chronic opioid therapy or with seizure history, naltrexone/bupropion is contraindicated.

Psychiatric medication modification is an often-overlooked aspect of obesity management. When antipsychotics or antidepressants contribute to weight gain, switching to weight-neutral alternatives is recommended: olanzapine to aripiprazole or quetiapine, or amitriptyline/mirtazapine to fluoxetine or sertraline. This must be done carefully with monitoring for psychiatric symptom relapse.

Phase 3: Bariatric Intervention

Indications for bariatric surgery include BMI $\ge 35\backslash geq\; 35$ (with or without comorbid), BMI 30-34.9 failing medical therapy, or BMI $\ge 30\backslash geq\; 30$ with type 2 DM. Absolute contraindications are inability to undergo general anesthesia, uncontrolled psychiatric disorder, active substance abuse, pregnancy, and active malignancy. Even patients with extreme BMI (>70) can undergo surgery safely.

Post-bariatric nutrition follows a strict progression: clear liquids only for 24-48 hours, full liquids with high protein from day 3-14, pureed foods at week 3, soft foods at week 4, gradual reintroduction of solids by weeks 6-8, and full regular diet by 2 months. Protein requirements post-surgery are 1.1-1.5 g/kg/day (up to 2 g/kg/day after biliopancreatic diversion). Lifelong micronutrient supplementation is mandatory, particularly vitamin B1 ($\ge 12\backslash geq\; 12$ mg/day), vitamin B12 (350-500 mcg/day PO or 1000 mcg/month IM), folate (400-800 mcg/day), iron, vitamin D3 (3000 IU/day targeting serum level $\ge 30\backslash geq\; 30$ ng/mL), and calcium (1200-2400 mg/day depending on procedure type).

Target and Timeline

The realistic weight loss target is 0.5-1 kg per week (Recommendation A). The initial goal is 5-10% of baseline body weight within the first 6 months. If this is unattainable, the minimum acceptable outcome is preventing further weight gain. Long-term maintenance targets 10-20% total weight loss from baseline.

05Differential Diagnosis and Distractors

Obesity itself has no differential diagnosis per the PNPK. However, the exam frequently tests whether the student can distinguish primary (exogenous) obesity from secondary causes and comorbid look-alikes.

06Traps and High-Yield Pearls

The most common mistake students make with obesity questions is treating BMI as the sole diagnostic and therapeutic criterion. The PNPK explicitly states that diagnosis is not limited to BMI cutoff values alone; the Edmonton Obesity Staging System must be applied to determine the presence and severity of complications (cardiometabolic, mechanical, and mental). A question may present a patient with BMI 26 but with uncontrolled type 2 DM, OSA, and depression, and the correct answer is that this patient warrants pharmacotherapy and possibly surgical referral, not just lifestyle counseling.

A second trap involves the Asia-Pacific BMI cutoffs. Students accustomed to WHO global criteria will miss the diagnosis entirely. For Asia-Pacific populations, overweight begins at BMI 23 and obesity at BMI 25, not 25 and 30 respectively.

Third, students often confuse the pharmacotherapy response checkpoint. After starting any anti-obesity medication, the patient must be reassessed at 3 months (12 weeks). A responder is someone who achieves $\ge 5\mathrm{\%}\backslash geq\; 5\backslash \%$ weight loss; for liraglutide, specifically, if <4% weight loss is achieved at 16 weeks, the drug must be discontinued. Continuing an ineffective drug is a wrong answer.

Fourth, the role of pharmacotherapy as adjuvant only is frequently tested. Medications are never first-line standalone therapy. Every patient must have a concurrent program of nutritional modification, structured physical activity, and behavioral intervention. A vignette that jumps straight to semaglutide without establishing lifestyle modification is testing whether you will choose the answer that includes the foundational therapy first.

Finally, bariatric surgery questions often hinge on the contraindication list. The absolute contraindications (inability to tolerate general anesthesia, uncontrolled psychiatric disorder, active substance abuse, pregnancy, active malignancy) must be memorized. A common distractor is offering surgery to a patient with uncontrolled schizophrenia or active IV drug use, both of which are absolute contraindications regardless of BMI.

The core competency being tested is the ability to stage obesity severity beyond BMI, select therapy intensity based on staging and comorbidity burden, and apply pharmacotherapy response thresholds to make evidence-based escalation decisions.