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For further information, see CMDT Part 29-04: Obesity

Key Features

Essentials of Diagnosis

  • Disorder of energy homeostasis; body mass index (BMI) > 30 kg/m2

  • Upper body obesity (abdomen and flank) of greater health consequence than lower body obesity (buttocks and thighs)

  • Associated comorbid conditions include

    • Diabetes mellitus

    • Hypertension

    • Hyperlipidemia

    • Heart disease

    • Stroke

    • Sleep apnea

General Considerations

  • Quantitative evaluation involves determination of BMI

  • BMI accurately reflects the presence of excess adipose tissue; it is calculated by dividing measured body weight in kilograms by the height in meters squared

    • Normal: BMI = 18.5–24.9 kg/m2

    • Overweight: BMI = 25–29.9 kg/m2

    • Class I obesity: BMI = 30–34.9 kg/m2

    • Class II obesity: BMI = 35–39.9 kg/m2

    • Class III (extreme) obesity: BMI ≥ 40 kg/m2

  • Increased abdominal circumference (> 102 cm in men and > 88 cm in women) or high waist/hip ratios (> 1.0 in men and > 0.85 in women) have a greater risk of weight-related comorbid conditions and early death than patients with the same BMI and lower ratios

  • Upper body obesity (excess adipose tissue around the waist and flank) is a greater health hazard than lower body obesity (adipose tissue in the thighs and buttocks)

  • Visceral fat within the abdominal cavity is more hazardous to health than subcutaneous fat around the abdomen


  • Survey data suggest that almost 40% of Americans have obesity

  • Both genetic and environmental factors contribute to the development of obesity

  • Twin studies have demonstrated that genetics account for 40–90% of the variation in BMI

  • Only a small percentage of human obesity is thought to be due to single gene mutations

  • Most obesity develops from the interactions of multiple genes, environmental factors, and behaviors

  • The rapid increase in obesity in the last several decades points to major roles for environmental and behavioral factors in its development

Clinical Findings

  • Medical history should determine the following:

    • Age at onset of weight gain

    • Recent weight changes

    • Family history of obesity

    • Occupational history

    • Eating and exercise behavior

    • Cigarette and alcohol use

    • Previous weight loss experience

    • Psychosocial factors, including assessment for depression and eating disorders

  • Physical examination should assess the

    • BMI

    • Degree and distribution of body fat

    • Overall nutritional status

    • Signs of secondary causes of obesity (eg, Cushing syndrome) found in < 1%


  • Blood pressure

  • Waist circumference

  • Fasting serum glucose and hemoglobin A1c

  • Comprehensive metabolic profile

  • Lipid panel



  • Can be considered in patients with a BMI ≥ 30 kg/m2 or a BMI ≥ 27 kg/m2 plus weight-related comorbidities

  • The most widely prescribed antiobesity medications approved by the FDA (Table 29–2) are

    • Phentermine

    • Orlistat

    • Phentermine/topiramate extended release (ER)

    • Naltrexone sustained release (SR)/bupropion SR

    • Liraglutide


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