Evaluation and Management of Obesity¶

Chapter 414 | Part 12: Endocrinology and Metabolism · Part 12 – Endocrinology & Metabolism · Chapter 414

Key Clinical Points¶

Obesity is a chronic, relapsing disease of energy imbalance driven by environmental and genetic factors.
BMI classification: Overweight (25.0–29.9 kg/m²), Obesity Class I (30.0–34.9), Class II (35.0–39.9), Class III (≥40).
Waist circumference is a surrogate for visceral adipose tissue; thresholds vary by ethnicity (e.g., Europeans: Men >94 cm, Women >80 cm).
AACE/ACE Staging: Stage 0 (no complications), Stage 1 (mild-moderate), Stage 2 (severe complications).
Treatment hierarchy: Lifestyle → Pharmacotherapy (BMI ≥30 or ≥27 with comorbidities) → Surgery (BMI ≥40 or ≥35 with comorbidities).
GLP-1 receptor agonists (Semaglutide, Tirzepatide) show high weight loss (~12.5% to 17.8%) but require caution in patients with medullary thyroid cancer.
Phentermine/topiramate (PHEN/TPM) shows ~8.0% weight loss; topiramate requires caution regarding glaucoma and kidney stones.
Very-low-calorie diets (VLCD) ≤800 kcal/d are for rapid weight loss in severe cases (e.g., OSA, poorly controlled diabetes).
Secondary causes of obesity include PCOS, hypothyroidism, Cushing's syndrome, and hypothalamic disease.
Obesity significantly increases risk for CVD, T2DM, OSA, NASH, osteoarthritis, and specific cancers (colorectal, kidney, pancreatic, esophageal, endometrial).

DEFINITION & CLASSIFICATION¶

• Definition (Harrison's 22e): Obesity is a medical disorder that has been greatly increasing in prevalence due to environmental factors... It is a chronic, relapsing disease of energy imbalance. • Pathophysiology: Highly heterogeneous; some cases are entirely genetic; others driven by biopsychosocial/behavioral factors. • BMI Calculation: weight (kg)/height (m)² or weight (lb)/height (in)² imes 703. • Waist Circumference: Surrogate for visceral adipose tissue; measured in horizontal plane above iliac crest for BMI ≤35 kg/m².

Table 414-1: Classification of Weight Status and Disease Risk • Overweight: BMI 25.0–29.9 • Obesity Class I: BMI 30.0–34.9 (High risk) • Obesity Class II: BMI 35.0–39.9 (Very high risk) • Extreme Obesity (Class III): BMI ≥40 (Extremely high risk)

Table 414-2: Ethnic-Specific Cutpoint Values for Waist Circumference • Europeans: Men >94 cm; Women >80 cm • South Asians/Chinese: Men >90 cm; Women >80 cm • Japanese: Men >85 cm; Women >90 cm

Staging Systems: • AACE/ACE Staging: → Stage 0: Overweight/Obese with no complications. → Stage 1: Over100% Overweight/Obese with mild-moderate complications. → Stage 2: Overweight/Obese with at least one severe complication. • Edmonton Obesity Staging System (EOSS): 5 graded categories (0–4) based on medical, functional, and psychological domains; independent of BMI.

EPIDEMIOLOGY¶

• Prevalence: >70% of U.S. adults are overweight or obese. • Trends: Rapidly increasing in industrialized world; rising rates in children/adolescents. • Risk Factors: → Environmental factors (ubiquitous) → Genetic variation → Biopsychosocial and behavioral factors (diet, physical activity) → Sedentary lifestyle (predictor of mortality independent of BMI).

ETIOLOGY & PATHOPHYSIOLOGY¶

• Core Mechanism: Disease of energy imbalance. • Contributing Factors: → Sleep deprivation → metabolic alterations in appetite, SNS overactivity, insulin sensitivity issues. → Stress → activation of adrenal cortical axis, elevated cortisol. • Insulin Resistance: Overnourished state leads to hyperinsulinemia; predisposes to T2DM (especially in those with genetic inability to maintain high insulin secretion).

CLINICAL FEATURES¶

• Symptoms & Signs: → Exertional dyspnea (increased work of breathing, pressure on diaphragm). → Sleep apnea (soft tissue enlargement, adipose depots around airways). → Acanthosis nigricans (velvety hyperpigmentation in axilla/groin due to insulin resistance). → Hidradenitis suppurativa (recurring boils, associated with obesity).

Table 414-3: Obesity-Related Organ Systems Review • Cardiovascular: Hypertension, CHF, Cor pulmonale, CAD, Stroke, Atrial fibrillation. • Respiratory: Dyspnea, OSA, Hypoventilation syndrome, Asthma. • Endocrine/Metabolic: PCOS, T2DM, Metabolic syndrome, Dyslipidemia. • Gastrointestinal: GERD (most common), Cholelithiasis (risk of colic, cholecystitis, pancreatitis). • Musculoskeletal: Osteoarthritis (knees/hips), Gout, Low back pain, Carpal tunnel. • Psychological: Depression, Body image disturbance. • Integumentary: Striae distensae, Cellulitis, Intertrigo, Acanthosis nigricans.

Specific Complications: • Fatty Liver Disease: Progression from steatosis → NASH → Fibrosis → Cirrhosis → Hepatocellular carcinoma. • Cancers: Risk increases by 10% for every 5 kg/m² increase in BMI. → Highest risk: Colorectal, kidney, pancreatic, esophageal adenocarcinoma, endometrial carcinoma. • Infection: Increased risk of poor outcomes in COVID-19; higher susceptibility to bacterial wound infections and sepsis.

DIFFERENTIAL DIAGNOSIS¶

• Secondary Causes (Require evaluation if suspected): → Polycystic ovarian syndrome → Hypothyroidism → Cushing's syndrome → Hypothalamic disease • Drug-Induced Weight Gain: → Diabetes meds: Insulin, sulfonylureas, thiazolidinediones. → Steroid hormones. → Antipsychotics: Clozapine, olanzapine, risperidone. → Mood stabilizers: Lithium. → Antidepressants: Tricyclics, MAOIs, paroxetine, mirtazapine. → Antiepileptics: Valproate, gabapentin, carbamazepine.

DIAGNOSTIC APPROACH¶

Focused Obesity-Related History: • Approach must be sensitive (obesity is a highly charged term). • Key questions: Factors for weight gain, impact on health, risk level, difficulties in management, goals/expectations, motivation, and type of help needed. • Assess sleep (regularity, duration, efficiency) and stress.
Physical Examination: • Determine degree and type of obesity.
Assessment of Complications: • Evaluate conditions listed in Table 414-3 (e.g., OSA, NASH, T2DM).
Assessment of Patient's Readiness to Change: • Balance of Motivation vs. Resistance. • Technique: 'Anchoring' on a scale of 0–10 (0 = not important/confident; 10 = very important/confident).

MANAGEMENT & TREATMENT¶

Initial Goals: • Improve complications, improve quality of life, reduce future risk. • Target: 8–10% weight loss over 6 months.
Lifestyle Management: • Diet: Reduce calories by 500–750 kcal/day OR prescribed diet of 1200–1500 kcal (women) / 1500–1800 kcal (men). • Strategy: Portion control, high fiber/protein, low energy density foods (soups, fruits, vegetables). • Very-low-calorie diets (VLCD): ≤800 kcal/day; used for rapid weight loss in severe cases (OSA, poorly controlled DM).
Pharmacotherapy (Table 414-5): • Phentermine: Sympathomimetic; 4.4% weight loss; Contra: Uncontrolled HTN. • Orlistat: Lipase inhibitor; 4.1% weight loss; Contra: Chronic malabsorption. • Phen/TPM: Sympathomimetic + GABA mod; 8.0% weight loss; Contra: HTN, glaucoma, kidney stones. • Nal/Bup: Opioid block + POMC activation; 5.1% weight loss; Contra: Seizures, bulimia/anorexia. • Liraglutide: GLP-1 agonist; 5.4% weight loss; Caution: Medullary thyroid cancer. • Semaglutide: GLP-1 agonist; 12.5% weight loss; Caution: Medullary thyroid cancer. • Tirzepatide: GLP-1/GIP dual agonist; 17.8% weight loss; Caution: Medullary thyroid cancer.
Bariatric Surgery (Table 414-4): • BMI 25–26.9: Lifestyle only. • BMI 27–29.9: Lifestyle + Pharmacotherapy (if comorbidities). • BMI 30–34.9: Lifestyle + Pharmacotherapy. • BMI 35–39.9: Lifestyle + Pharmacotherapy + Surgery (if comorbidities). • BMI ≥40: Lifestyle + Pharmacotherapy + Surgery.

KEY PEARLS & HIGH-YIELD POINTS¶

• Clinical Pearl: Weight loss depends primarily on reduction of total caloric intake and adherence, not specific macronutrient proportions (low-carb vs. low-fat). • Clinical Pearl: Use of meal replacements can result in 7–8% weight loss. • High Yield: Identify secondary causes like Cushing's or Hypothyroidism early to ensure appropriate treatment. • High Yield: Tirzepatide offers the highest reported weight loss (17.8%) among listed medications but requires screening for medullary thyroid cancer risk.

Reference Tables¶

TABLE 414-1 Classification of Weight Status and Disease Risk CLASSIFICATION Underweight Healthy weight Overweight…¶

Harrison's 22e, p.3188

CLASSIFICATION	BODY MASS INDEX (kg/m2)	OBESITY CLASS	DISEASE RISK
Underweight	<18.5	—	—
	18.5–24.9	—
Overweight	25.0–29.9	—	Increased
	30.0–34.9	I
Obesity	35.0–39.9	II	Very high
	≥40	III

TABLE 414-2 Ethnic-Specific Cutpoint Values for Waist Circumference¶