• A serious, progressive, and chronic disease characterized by excess adipose tissue to the extent that health may be impaired, typically quantified in adults by body mass index (BMI) (kg/m2), ≥30 kg/m2
  • Overweight: BMI 25 to 29.9 kg/m2
  • Obesity is categorized into three classes:
    • Class 1 obesity is BMI 30 to 34.9 kg/m2.
    • Class 2 obesity is BMI 35 to 39.9 kg/m2.
    • Class 3 obesity (also called severe obesity) is BMI ≥40 kg/m2.
  • Obesity is preventable and associated with negative health outcomes. Abdominal obesity increases the risk of morbidity and mortality.

Geriatric Considerations
Aging is associated with changes in body composition including sarcopenia, decreased bone mineral density, and accumulation of visceral fat.


Predominant age: Incidence rises in the early 20s and peaks at middle-aged adults 40 to 59 years old.

42% of U.S. adults and 20% of children and adolescents (2 to 19 years old) meet BMI criteria for obesity.

Pediatric Considerations

  • The United States Preventive Services Task Force (USPSTF) recommends screening for obesity in children and adolescents ≥6 years old and referring those with positive screens to comprehensive, intensive behavioral interventions (grade B recommendation).
  • Pediatric classifications by age- and sex-specific WHO or CDC growth curves:
    • Overweight: BMI ≥85th to <95th percentile
    • Obesity (Class I): BMI ≥95th percentile
    • Severe Obesity:
      • Class II: BMI ≥120th percentile of the 95th percentile
      • Class III: BMI ≥140th percentile of the 95th percentile
  • Obesity during adolescence is strongly associated with obesity in adulthood, largely in part to eating habits and lifestyle choices.
  • Obesity in children is associated with mental health and psychological issues, low self-esteem, and impaired quality of life.

Etiology and Pathophysiology

  • Multifactorial process where genetic, environmental, behavioral, and psychosocial issues lead to an imbalance between energy intake and expenditure
  • Adipocytes (fat cells) produce peptides called adiponectin and leptin. Adiponectin improves insulin sensitivity, and the absence of leptin has been associated with severe obesity.
  • After obesity has developed, an individual’s neuronal signaling is altered to decrease satiety, and adipocyte hypertrophy leads to both local and systemic inflammation.


  • Genetic syndromes such as Prader-Willi and Bardet-Biedl are found in a minority of people with obesity.
  • Multiple genes are implicated in obesity, and certain genotypes may account for differences in weight loss response following dietary changes.

Risk Factors

  • Parental obesity
  • Sedentary lifestyle and lack of regular physical activity
  • Poor nutrition, especially consumption of calorie-dense food, and limited access to fresh produce/foods
  • Stress and mental illness

General Prevention

  • Encourage regular physical activity with a goal of at least 150 minutes of moderate-intensity activity per week (e.g., 30 minutes of exercise, 5 days/week), and a well-balanced diet with appropriate portion sizes.
  • Avoid calorie-dense and nutrient-poor foods such as sugar-sweetened beverages and processed foods.
  • Early preventive counseling, especially in children and young adults

Commonly Associated Conditions

  • Type 2 diabetes, HTN, hyperlipidemia
  • Coronary artery disease (CAD), congestive heart failure
  • Obstructive sleep apnea
  • Osteoarthritis
  • Nonalcoholic fatty liver disease
  • Mood disorders: anxiety, depression
  • Polycystic ovarian syndrome

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