Measuring Obesity

How Is Obesity Measured?

Endocrinologists and other healthcare professionals measure obesity using two primary tools:

1. Body mass index, or BMI, which measures weight in proportion to height; and
2. Waist circumference, which measures abdominal fat. (Typically used in research only)

What is Body Mass Index (BMI)?
Body mass index, or BMI, is the most common measure of obesity by an individual’s weight relative to his or her height. Evaluating BMI helps physicians determine the severity of an individual’s condition and his or her class of obesity.

What is Waist Circumference?
Physicians measure waist circumference as a way to assess obesity by measuring a patient’s abdominal fat – a predictor of risk factors for obesity-related medical conditions⁹. Men who have a waist measurement greater than 40 inches, and women with a measurement greater than 35 inches are likely considered to be overweight. They are, therefore, at higher risk for obesity and obesity-related diseases, including cardiovascular disease, metabolic syndrome, PCOS, diabetes, and hypertension¹⁰. It is important to note that clinicians do not typically use waist circumference values.

The following chart shows the relationship between BMI (body mass index), waist circumference and the risk of obesity-related diseases.

In the research setting, physicians sometimes use computed tomography to measure obesity – a method of examining body organs by scanning them with X-rays and using a computer to construct the resulting image – to measure abdominal fat distribution. Magnetic resonance imaging (MRI) can also be used to evaluate obesity by an individual's distribution of abdominal fat by providing an unparalled view of the body. Electrical impedance is the quickest method for evaluating obesity by measuring body fat percentage. As part of the procedure – which is non-invasive and better suited for people with higher percentages of body fat or those who would feel uncomfortable with having skin-fold measurements taken – electrodes are attached to different areas of the body and a current is then sent to estimate total body water. As muscle contains a greater percentage of water, the more water a subject’s body contains, the lower his or her body fat measurement will be. Computed tomography, MRI and electrical impedance tend to be expensive and impractical for routine, daily clinical use among healthcare providers, as they require advanced technological tools¹¹. For this reason, these obesity evaluations are commonly limited to research, not clinical, applications.