What are the criteria for obesity?

Criteria for Obesity

Obesity is defined as a BMI of 30 kg/m² or greater, with overweight defined as a BMI of 25-29.9 kg/m². 1

BMI Classification for Adults

• Underweight: BMI < 18.5 kg/m² 1
• Normal or acceptable weight: BMI 18.5-24.9 kg/m² 1
• Overweight: BMI 25-29.9 kg/m² 1
• Obesity: BMI ≥ 30 kg/m² 1
  • Class 1 (mild): BMI 30-34.9 kg/m² 1
  • Class 2 (moderate): BMI 35-39.9 kg/m² 1
  • Class 3 (severe): BMI ≥ 40 kg/m² 1
  • Class 4 (super obesity): BMI > 50 kg/m² 2
  • Class 5: BMI > 60 kg/m² 2

BMI Classification for Children (2-18 years)

• Overweight: BMI of 85th to 94th percentile 1
• Obese: BMI of 95th percentile or BMI of 30 kg/m², whichever is lower 1
• Severe obesity: 99th percentile BMI 1
  • 30-32 kg/m² for youths 10-12 years of age 1
  • 34 kg/m² for youths 14-16 years of age 1

BMI Calculation

BMI is calculated as body weight in kilograms divided by height in meters squared (kg/m²). If using pounds and inches, the formula is: [weight (in pounds)/height (in inches)²] × 703 1

Limitations of BMI

• BMI does not distinguish between lean and fat mass, potentially misclassifying individuals with high muscle mass as overweight or obese 1
• BMI has good specificity (90%) but low sensitivity (50%) for diagnosing excess adiposity 1
• BMI may not correlate as well with body fat in certain age, sex, and ethnic groups 1
• Women typically have higher percentages of body fat than men at similar BMI levels 1

Ethnic-Specific Considerations

• Asian populations, including Indians, have greater adiposity and higher comorbidity risks at lower BMI levels 1, 3
• BMI cut points between 23-27 kg/m² more accurately identify obesity in Asian populations 1, 3
• For Asian populations, overweight may be defined as BMI ≥ 23 kg/m² with obesity thresholds lower than Western populations 3

Additional Measurements for Assessing Obesity

Waist Circumference (Central Adiposity)

• Men: > 102 cm (> 40 inches) indicates increased cardiovascular risk 1
• Women: > 88 cm (> 35 inches) indicates increased cardiovascular risk 1
• Asian men: ≥ 90 cm 3
• Asian women: ≥ 80 cm 3

Waist-to-Hip Ratio

• Men: > 0.9 indicates central adiposity 1
• Women: > 0.85 indicates central adiposity 1

Waist-to-Height Ratio

• ≥ 0.5 can identify individuals at risk of obesity-related metabolic abnormalities 3

Clinical Significance

• Central adiposity (abdominal fat) increases risk for cardiovascular and other diseases independent of overall obesity 1
• Waist circumference thresholds are not reliable for patients with a BMI greater than 35 1
• Elevated BMI and waist circumference are associated with increased health risks and obesity-related comorbidities 1
• Obesity is linked to numerous pathologic conditions including cardiovascular disease, type 2 diabetes, sleep apnea, cancer, and gastrointestinal disorders 1

Common Pitfalls in Obesity Assessment

• Relying solely on BMI without considering body composition or fat distribution 1, 4
• Failing to consider ethnic-specific differences in body composition 3
• Not measuring waist circumference in addition to BMI to assess central adiposity 1
• Using BMI alone to diagnose obesity in individuals with high muscle mass 1, 4