What are the classes of obesity and how are they managed?

Obesity Classes and Management

Obesity is classified into three main classes based on BMI: class I (BMI 30-34.9), class II (BMI 35-39.9), and class III (BMI ≥40), with management strategies intensifying as BMI increases to address the escalating health risks associated with higher obesity classes. 1

Classification of Obesity

Body Mass Index (BMI) is the most widely used method to classify obesity, calculated as weight in kilograms divided by height in meters squared (kg/m²):

• Underweight: BMI < 18.5 kg/m²
• Normal weight: 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 obesity: BMI ≥40 kg/m² 1

Important Considerations in Classification

• Ethnic variations: Asian populations may require lower BMI thresholds (≥25 or ≥27.5) for obesity diagnosis due to higher cardiometabolic risk at lower BMI levels 1
• Additional measurements: Waist circumference should be used alongside BMI, especially for BMI 25-34.9, with high-risk thresholds being ≥102 cm (>40 inches) for men and ≥88 cm (>35 inches) for women 1
• Edmonton Obesity Staging System: Classifies risk based on factors independent of BMI; higher severity scores are associated with increased all-cause mortality (hazard ratio 2.69) 1

Health Risks Associated with Obesity

Obesity significantly increases morbidity and mortality through:

• Cardiovascular disease: Men with BMI 30-39.9 have cardiovascular event rates of 20.21 per 1000 person-years vs. 13.72 for normal BMI; women with BMI 30-39.9 have rates of 9.97 vs. 6.37 for normal BMI 1
• Metabolic complications: Type 2 diabetes, hypertension, dyslipidemia
• Mechanical complications: Obstructive sleep apnea, osteoarthritis
• Other conditions: Asthma, nonalcoholic fatty liver disease 1

Management Approach by Obesity Class

For All Obesity Classes (I-III)

1. Behavioral interventions:

   • High-intensity counseling (>1 session/month for first 3 months) 1
   • Focus on nutrition education, diet and exercise counseling
   • Behavioral strategies using the 5-A framework (Assess, Advise, Agree, Assist, Arrange) 1
   • Goal of 5-10% weight loss improves health outcomes 1

2. Nutritional therapy:

   • Reduce total caloric intake
   • Dietary strategies based on patient preferences 1

3. Physical activity:

   • Regular exercise (even without calorie reduction typically causes 2-3 kg weight loss)
   • Critical for weight maintenance 1

For Class II Obesity (BMI 35-39.9) with Comorbidities and Class III Obesity (BMI ≥40)

In addition to the above interventions:

1. Pharmacotherapy:

   • FDA-approved medications for long-term use:
     • GLP-1 agonists (semaglutide, liraglutide)
     • Tirzepatide (GIP/GLP-1 agonist) - most effective with 21% weight loss at 72 weeks
     • Phentermine-topiramate
     • Naltrexone-bupropion
     • Orlistat 1

2. Bariatric procedures:

   • Endoscopic procedures: intragastric balloon, endoscopic sleeve gastroplasty (10-13% weight loss)
   • Bariatric surgeries: laparoscopic sleeve gastrectomy, Roux-en-Y gastric bypass (25-30% weight loss at 12 months) 1

Monitoring and Follow-up

• For all patients with obesity: measure height, weight, BMI, and body fat distribution at least annually 1
• During active weight management: increase monitoring to at least every 3 months 1
• Maintain long-term follow-up as weight regain occurs in ≥25% of participants at 2-year follow-up 1

Special Considerations

• Medication review: Evaluate and consider alternatives to medications that cause weight gain (e.g., certain antidepressants like mirtazapine, amitriptyline; antihyperglycemics like glyburide or insulin) 1
• Person-centered approach: Use person-first language (e.g., "person with obesity" rather than "obese person") 1
• Privacy: Ensure accommodations are made for privacy during anthropometric measurements 1

Pitfalls to Avoid

• Relying solely on BMI: BMI does not directly measure adiposity or account for individual differences in risk 1
• Ignoring weight distribution: Central adiposity increases cardiovascular risk independent of BMI 1
• Underestimating the importance of sustained intervention: Weight regain is common without ongoing support 1
• Neglecting psychological aspects: Weight stigma and bias can impede effective treatment 2

By implementing a structured approach to obesity management based on obesity class and individual risk factors, clinicians can significantly improve morbidity, mortality, and quality of life outcomes for patients with obesity.