From the Guidelines
Obesity is classified into three categories based on Body Mass Index (BMI): Class 1 obesity (BMI 30.0-34.9 kg/m²), Class 2 obesity (BMI 35.0-39.9 kg/m²), and Class 3 obesity (BMI ≥40 kg/m²). These classifications are crucial for healthcare providers to assess health risks and determine appropriate interventions 1. As BMI increases, so does the risk of developing obesity-related conditions like type 2 diabetes, hypertension, sleep apnea, and cardiovascular disease.
Key Considerations
- BMI is an imperfect measure of health and should not be relied on as a sole diagnostic and staging tool 1.
- A person-centered communication style that uses inclusive and nonjudgmental language and active listening is essential to optimize health outcomes and health-related quality of life 1.
- Treatment approaches vary by obesity class, with more intensive interventions typically recommended for higher classes.
Classification Details
- Class 1 obesity: BMI 30.0-34.9 kg/m²
- Class 2 obesity: BMI 35.0-39.9 kg/m²
- Class 3 obesity: BMI ≥40 kg/m²
Importance of Comprehensive Assessment
For a comprehensive health assessment, BMI should be considered alongside other measurements such as waist circumference, which helps evaluate abdominal fat that poses particular health risks 1. This approach ensures that healthcare providers can develop personalized treatment plans that address the unique needs and health status of each individual.
Recent Guidelines
The most recent guidelines from 2025 emphasize the importance of individualizing treatment approaches for obesity based on the person’s medical history, life circumstances, preferences, and motivation 1. This personalized approach is critical for improving health outcomes and quality of life for individuals with obesity.
From the Research
Classification of Obesity
The classification of obesity is typically based on the body mass index (BMI), which is calculated by dividing the person's weight in kilograms by the square of their height in meters.
- A BMI of 30 kg/m2 or greater is considered obese 2
- A BMI of 27 kg/m2 or greater with weight-related comorbidities is also considered for obesity treatment 2
- A BMI of 40 kg/m2 or greater is considered for bariatric surgery referral 3
- A BMI of 30 to 39.9 kg/m2 with obesity-related comorbid conditions is considered for adjustable gastric banding or other bariatric surgical approaches 3
Obesity Treatment
Obesity treatment involves a combination of lifestyle modifications, behavioral interventions, and pharmacotherapy.
- Lifestyle modifications include dietary strategies emphasizing reduced caloric intake and physical activity 3
- Behavioral interventions include motivational interviewing and encouraging physical activity 3
- Pharmacotherapy includes medications such as orlistat, lorcaserin, liraglutide, phentermine/topiramate, and naltrexone/bupropion 4, 2, 3
Obesity Medications
Obesity medications are designed to manipulate the control of hunger and satiety in the central nervous system.
- Phentermine and orlistat were the only medications available to treat obesity in the USA prior to 2012 4
- Newer medications include lorcaserin, phentermine/topiramate extended release, naltrexone ER/wellbutrin ER, and liraglutide 4
- Each medication has a unique mechanism of action and side effect profile 4