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  • Excess adipose tissue; body mass index (BMI) greater than 30.

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

  • Many associated comorbid conditions, including type 2 diabetes mellitus, hypertension, hyperlipidemia, heart disease, stroke, and obstructive sleep apnea.


Obesity is a multifactorial, chronic disease characterized by an accumulation of visceral and subcutaneous fat. Obesity predisposes to a wide variety of comorbid conditions. The BMI typically correlates with excess adipose tissue. It is calculated by dividing body weight in kilograms by height in meters squared (eTable 29–8). The National Institutes of Health (NIH) defines a normal BMI as 18.5–24.9. Overweight is defined as BMI 25–29.9. Class I obesity is 30–34.9, class II obesity is 35–39.9, and class III obesity is BMI greater than or equal to 40. Upper body obesity (excess fat around the waist and flank) is a greater health hazard than lower body obesity (fat in the thighs and buttocks). Patients with obesity and increased abdominal circumference (greater than 102 cm or 40 inches in men and 88 cm or 35 inches in women) or high waist–hip ratios (greater than 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. Furthermore, visceral fat within the abdominal cavity is more hazardous to health than subcutaneous fat around the abdomen. US survey data demonstrate that almost 40% of Americans have obesity. The medical costs associated with obesity are tremendous. The latest published estimate was 147 billion US dollars in 2008.


Obesity is associated with significant increases in both morbidity and mortality. Many disorders occur with greater frequency in patients with obesity (eFigure 29–1). These include hypertension, type 2 diabetes mellitus, hyperlipidemia, coronary artery disease, and degenerative joint disease. Certain cancers, thromboembolic disorders, digestive tract diseases (gallbladder disease, gastroesophageal reflux disease), and skin disorders are more prevalent in patients with obesity. Surgical and obstetric risks are also greater. Patients with obesity have an increased risk of pulmonary functional impairment including obstructive sleep apnea, endocrine abnormalities, proteinuria, and increased hemoglobin concentration. Patients with obesity also have increased rates of major depression and binge eating disorder, and many have experienced weight bias.

eFigure 29–1.

Role of obesity in the pathophysiology of disease. Some ways whereby obesity contributes to disease. Short arrows refer to a change in the indicated parameter, and long arrows indicate a consequence of that change. In some cases, evidence is epidemiologic; in others, it is experimental. (Modified and reproduced, with permission, from Bray GA. Pathophysiology of obesity. Am J Clin Nutr. 1992;55:488S.)


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

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