Obesity Medicine: Pharmacotherapy & Metabolic Surgery

Clinical meaning

Obesity is a chronic, relapsing neuroendocrine disease characterized by dysregulation of the hypothalamic appetite-satiety axis, leading to excessive energy storage as adipose tissue. The hypothalamus integrates peripheral signals from adipose tissue (leptin, adiponectin), the gastrointestinal tract (ghrelin from the stomach, GLP-1 and PYY from the ileum, cholecystokinin from the duodenum), the pancreas (insulin), and the brainstem to regulate energy balance through orexigenic (appetite-stimulating: NPY/AgRP neurons) and anorexigenic (appetite-suppressing: POMC/CART neurons) pathways. In obesity, leptin resistance develops despite high circulating leptin levels, reducing the hypothalamic satiety signal. Adipose tissue functions as an endocrine organ, producing pro-inflammatory cytokines (TNF-alpha, IL-6, resistin) that drive insulin resistance, endothelial dysfunction, and systemic chronic low-grade inflammation. Visceral adipose tissue is metabolically more active and pathogenic than subcutaneous fat. Anti-obesity pharmacotherapy targets multiple pathways: GLP-1 receptor agonists (semaglutide, liraglutide) activate central satiety pathways and delay gastric emptying; phentermine/topiramate combines norepinephrine release with GABAergic appetite suppression; naltrexone/bupropion blocks opioid-mediated reward eating while enhancing POMC neuron activity; and orlistat inhibits pancreatic lipase reducing dietary fat absorption by 30%. Metabolic surgery (Roux-en-Y gastric bypass, sleeve gastrectomy) produces weight loss through restrictive mechanisms (reduced gastric volume), malabsorptive mechanisms (bypassing duodenum and proximal jejunum), and profound hormonal changes (increased GLP-1, PYY, reduced ghrelin) that alter appetite and improve glucose homeostasis independent of weight loss. The NP evaluates candidates using a comprehensive approach including BMI classification (with waist circumference for cardiometabolic risk stratification), Edmonton Obesity Staging System for functional impairment, evaluation of obesity-related comorbidities, psychiatric screening, and shared decision-making regarding pharmacotherapy versus surgical intervention.

Diagnosis & workup

Diagnostics & workup: - BMI classification with waist circumference: Class I (30-34.9), Class II (35-39.9), Class III (40+); waist circumference above 40 inches (males) or 35 inches (females) indicates elevated cardiometabolic risk even at lower BMI - Metabolic panel: fasting glucose and HbA1c (diabetes screening), lipid panel (dyslipidemia), hepatic panel with ALT/AST (NAFLD screening -- elevated ALT suggests steatohepatitis), uric acid (gout risk) - Thyroid function tests: TSH and free T4 to exclude hypothyroidism as contributing factor; subclinical hypothyroidism (TSH 5-10 with normal T4) may contribute modestly to weight - Fasting insulin and HOMA-IR: assess insulin resistance severity; elevated fasting insulin with glucose suggests hyperinsulinemia driving lipogenesis and hunger - Sleep study (polysomnography): screen for obstructive sleep apnea using STOP-BANG questionnaire (score 3+ indicates moderate-to-high risk); untreated OSA impairs weight loss efforts - Edmonton Obesity Staging System: stage 0 (no apparent risk factors) through stage 4 (severe disabilities from obesity-related conditions); guides treatment intensity -- stages 2-4 warrant pharmacotherapy or surgical consideration - Body composition analysis: DEXA scan for precise lean mass and fat mass quantification; bioelectrical impedance for serial monitoring; sarcopenic obesity (low muscle mass with excess fat) carries highest metabolic risk

Risk factors: - Genetic predisposition (heritability of BMI is 40-70%; over 200 genetic loci identified; monogenic obesity from MC4R mutations accounts for 2-6% of severe early-onset obesity) - Obesogenic environment: high-calorie ultra-processed food availability, sedentary occupations, insufficient walkable infrastructure, food deserts limiting access to nutritious foods - Endocrine disorders contributing to weight gain: hypothyroidism, Cushing syndrome, polycystic ovary syndrome (PCOS), hypogonadism, growth hormone deficiency, insulinoma - Medications causing significant weight gain: atypical antipsychotics (olanzapine, clozapine average 5-10 kg in first year), corticosteroids, insulin, sulfonylureas, TCA antidepressants, valproic acid, gabapentin/pregabalin - Sleep deprivation and circadian disruption (reduced leptin, elevated ghrelin, increased cortisol, insulin resistance; shift work increases obesity risk by 25-30%) - Psychological factors: binge eating disorder (present in 25-50% of bariatric surgery candidates), emotional eating, adverse childhood experiences, depression, and PTSD - Early-life factors: maternal gestational diabetes (fetal programming), formula feeding versus breastfeeding, rapid infant weight gain, childhood obesity (80% of obese adolescents become obese adults)

Clinical meaning

Your next step on FNP

Practice this topic

Review related lessons

FNP CAT

Diagnosis & workup

Management

Prescribing & monitoring

Takeaways

Your next step on FNP

Practice this topic

Review related lessons

FNP CAT

Clinical meaning

Practice questions for this topic

Your next step on FNP

Practice this topic

Review related lessons

FNP CAT

Diagnosis & workup

Practice questions for this topic

Your next step on FNP

Practice this topic

Review related lessons

FNP CAT