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Source: Chen JT, Sheehan AH, Yanovski JA, Calis KA. Obesity. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. Accessed May 16, 2017.


  • State of excess body fat as determined by measures of adiposity.

    • Imbalance between energy intake and energy expenditure over time, resulting in increased energy storage.


  • Obesity occurs when there is increased energy storage resulting from an imbalance between energy intake and energy expenditure over time.


  • Many neurotransmitters and neuropeptides stimulate or depress brain’s appetite network, impacting total calorie intake.

  • Net balance of energy ingested relative to energy expended over time determines degree of obesity.

    • Metabolic rate largest determinant of energy expenditure.

    • Amount of physical activity contributing factor.

  • Adrenergic stimulation activates lipolysis in fat cells and increases energy expenditure in adipose tissue and skeletal muscle.

    • Major types of adipose tissue.

      • White, which manufactures, stores, and releases lipid.

      • Brown, which dissipates energy via uncoupled mitochondrial respiration.


  • Prevalence.

    • Varies by sex among racial and ethnic minorities in the United States.

    • Increases with age until eighth decade.

    • Increased with lower socioeconomic class and educational achievement.


  • Increased level of physical activity.

  • Decreased caloric intake relative to physical activity.


  • Sedentary lifestyle.

  • Association with other obese individuals.

  • Lower socioeconomic status.

  • Lower educational achievement.


  • Amount of excess fat and its distribution regionally in body is important clinically.

    • Central obesity reflects high levels of intra-abdominal or visceral fat associated with development of hypertension, dyslipidemia, type 2 diabetes, and cardiovascular disease.

  • Classification of excess weight is defined by body mass index (BMI):

    • Overweight: BMI 25–29.9 kg/m2

    • Obese: BMI 30–39.9 kg/m2

    • Extremely obese: BMI 40 kg/m2 and over.


  • BMI >25, calculated as weight (kg) divided by square of height (m2).

  • Waist circumference (WC) >40 inches (102 cm) for men and >35 inches (89 cm) for women (narrowest circumference between the last rib and top of iliac crest)

  • Both of above are independent predictors of disease risk (Table 1).

TABLE 1.abClassification of Overweight and Obesity by Body Mass Index (BMI), Waist Circumference, and Associated Disease Risk

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