Diagnosis of Obesity

Although obesity is still defined based on body mass index (BMI) (Figure 2), that marker is imperfect at best. In 2023, the American Medical Association released a statement noting “numerous concerns” with the way BMI is used to measure body fat and diagnose obesity.5

Figure 2. Obesity in Adults6

A study published in 2019 redefined BMI’s threshold by sex and race/ethnicity based on association with metabolic disease, thereby linking the definition of obesity to future prediction of medical morbidity and mortality. The authors used US NHANES data from 1999 to 2016 to estimate the distribution of BMI, as well as 3 metabolic disease risk factors: hypertension, dyslipidemia, and diabetes and determined projected changes in population prevalence if the new thresholds were adopted.

This showed that if obesity were defined by its correlation with the metabolic risk factors, the BMI cutoffs to define obesity would change for specific race/ethnicity and sex subgroups instead of a single BMI (Figure 3).7

Figure 3. BMI Adjustment for Race, Gender, and Obesity-Related Disease7

In its statement, the AMA recommended that clinicians use a variety of factors in addition to BMI to determine obesity: visceral fat, body adiposity index, body composition, relative fat mass, waist circumference, and genetic and metabolic factors.5

Nonetheless, the most recent guidelines from the American Association of Clinical Endocrinology, the American Heart Association, the American College of Cardiology, and The Obesity Society still recommend BMI as the primary screening tool for obesity.8, 9 However, the guidelines also note that BMI does not indicate the degree to which the weight may be affecting the health of individuals. Thus, clinicians must consider a patient’s individual risk and presence of obesity-related complications when determining if any treatment is necessary.10

When assessing a patient with obesity, clinicians should ask about weight gain and loss history, dietary habits, physical activity, family history of obesity, and other medical conditions or medications that may affect weight. They should then assess the need to lose weight. If weight loss is advised, it is important to assess the patient’s readiness to make change and identify barriers to success, determine weight loss and health goals, and then identify intervention strategies.8


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