What BMI Measures — and What It Does Not
BMI is calculated by dividing weight in kilograms by height in meters squared (kg/m²). It correlates reasonably well with body fat at the population level and is used in clinical guidelines to define eligibility for weight management treatments, including clinical trial enrollment criteria. However, BMI does not directly measure body fat percentage, does not distinguish between fat mass and lean mass, and does not account for fat distribution. Two people with identical BMIs can have very different metabolic risk profiles.
Source: CDC BMI for Adults — cdc.gov/bmi
Limitations of BMI as an Individual Metric
BMI may overestimate adiposity in people with high muscle mass (such as athletes) and underestimate it in people with low muscle mass (such as older adults). BMI thresholds were developed primarily from data on white European populations and may not accurately reflect health risk across all ethnic groups. For example, some Asian populations have higher metabolic risk at lower BMI values. Clinicians often use BMI alongside other measures for a more complete picture.
Waist Circumference and Metabolic Risk
Waist circumference is a measure of abdominal fat, which is more strongly associated with cardiometabolic risk than overall body fat. The CDC and NIH identify elevated waist circumference as an independent risk factor for type 2 diabetes, cardiovascular disease, and metabolic syndrome. General clinical thresholds: for men, a waist circumference above 40 inches (102 cm) is associated with increased risk; for women, above 35 inches (88 cm). These thresholds may differ by ethnicity.
Source: CDC — cdc.gov/bmi
How Clinicians Use These Metrics
In clinical practice, BMI is used to classify weight status and determine eligibility for treatments. Most FDA-approved weight management medications require a BMI of 30 or higher, or 27 or higher with at least one weight-related comorbidity. Retatrutide clinical trials use similar criteria. Waist circumference is often assessed alongside BMI to evaluate cardiometabolic risk. Neither metric alone determines treatment decisions — clinicians consider the full clinical picture.
