Body mass index, or BMI, is a way to quantify whether you are underweight, a healthy weight, overweight or obese. The calculations are the same for adult men and women and for people of different ethnic groups, ages and activity levels, even though these factors can affect BMI. Research suggests that BMI may not provide an accurate measurement of obesity.
What Is BMI?
BMI is a way to calculate whether you are a healthy weight. The formula involves dividing weight by height squared, then multiplying by 703. A woman who is 5 feet 5 inches tall and weighs 150 lbs. would have a body mass index of 24.96, which is just within the range of normal weight, according to the U.S. Centers for Disease Control and Prevention, or CDC. The CDC provides an automatic BMI calculator on its website.
Standard weight status categories are the same for people age 20 or older, regardless of gender. Adults with a BMI below 18.5 are considered underweight. Those whose BMI is between 18.5 and 24.9 are fall within the healthy weight range. A BMI of 15.0 to 29.9 indicates that you are overweight, and those whose BMI is 30 or higher are classified as obese. Separate scales, which take both age and gender into account, are available on the CDC site for children and teens.
While providing a single standard for all adults, the CDC acknowledges that the correlation between BMI and body composition varies by gender, age and race. For instance, at the same BMI, women tend to have more body fat than men, and older people tend to have more than those who are younger. In addition, athletes who have built up a lot of muscle may have high BMIs without having much body fat.
University of Texas at Galveston research published in “Obstetrics and Gynecology” suggests that the cut-off for obesity, a BMI of 30, may be too high. Researchers studied 555 women age 20 to 33. Using BMI as a measurement, 37 percent of the women were obese. However, using a World Health Organization guideline of 35 percent or more body fat as the cut-off, 63 percent of the women were found to be obese. In addition, white and Hispanic women were found to have 2.9 percent more body fat than black women with the same BMI.
- Centers for Disease Control and Prevention: About BMI for Adults
- “Obstetrics and Gynecology”; Accuracy of Current Body Mass Index Obesity Classification for White, Black and Hispanic Reproductive-Age Women; Mahbubur Rahman, MD, PhD, and Abbey B. Berenson, MD, MMS; May 2010
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This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or JillianMichaels.com.