The Dirty Truth Behind Body Mass Index

In 2004, the Centers of Disease Control and Prevention (CDC) labeled obesity as the number one health risk facing Americans. According to a study published in the Journal of the American Medical Association, obesity affects 32 percent of adult men and 35.5 percent of adult women. While these statistics are alarming, it's important to understand the truth behind the numbers.

The CDC defines obesity as an adult with a body mass index (BMI) over 30. Those with a BMI between 25 and 29.9 are considered overweight. But what is BMI exactly? It can be calculated using the following formula:

BMI = 705 x Body Weight (in pounds) ÷ [height (in inches) x height (in inches)]

For example:

A person who is 5 feet 6 inches (66 inches) tall and weighs 155 pounds has a BMI of 25:

BMI = 705 x 155 ÷ (66 x 66) = 25

While a person who is 5'6" and weighs 155 pounds may not sound (or look) like your typical overweight individual, according to their BMI and the definitions set forth by the CDC, they are.

So, What Does BMI Mean for You?

It is essential to remember that while BMI correlates with the amount of body fat, BMI does not directly measure body fat—it does account for lean muscle mass as well. Athletes, for instance, may have a high body mass index despite not having excess body fat.

BMI should be considered an indicator of health risk, rather than a hard-and-fast rule. According to the National Heart, Lung, and Blood Institute, those with a high body mass index should also assess their health by the following guidelines:

  • Waist circumference. The more weight you carry around your mid-section, the higher at risk you are for type 2 diabetes and cardiovascular conditions. Women with a waist size of 35 inches or higher and men 40 inches or higher are considered to be at high risk.
  • Other risk factors. Inactivity, poor diet, smoking, and high blood pressure will put you at an increased risk of health complications. 

Body mass index is not the be-and-end-all when it comes to determining obesity or assessing your health. However, if your high BMI is coupled with a large waist circumference and secondary risk factors, consult your health professional to work out a weight loss plan that is right for you.




National Heart, Lung, and Blood Institute
Assessing Your Weight and Health Risk

Overweight and Obesity
Centers for Disease Control and Prevention

Prevalence and Trends in Obesity Among US Adults, 1999-2008
Katherine M. Flegal, PhD; Margaret D. Carroll, MSPH; Cynthia L. Ogden, PhD; Lester R. Curtin, PhD