Nutrition-wise blog

BMI may underestimate obesity in women

By Jennifer K. Nelson, R.D., L.D. and Katherine Zeratsky, R.D., L.D. May 8, 2010

Attention young ladies — you're fatter than you think.

At least, that's the conclusion of a study recently published in the journal "Obstetrics and Gynecology." The study offers evidence that body mass index (BMI) — the standard for determining whether someone is obese — may not be accurate in women between 20 and 33 years of age. In fact, BMI failed to identify nearly half of the women in the study who were obese.

BMI is calculated by taking your weight in kilograms and dividing it by your height in meters squared. This method has been used to classify overweight and obesity for decades. BMI is also used to determine weight loss strategies, including whether weight loss surgery is indicated — and whether insurance will cover it.

How did researchers uncover the BMI problem? In addition to calculating BMI scores, they used body scans to determine body fat composition. Based on BMI, 37 percent of the women were considered obese. However, the body scans revealed that 63 percent of the women were actually obese. The study's authors suggest that additional research is needed to determine more accurate BMI cutoffs for women.

So what? This means we're fatter than we thought? It also means that the obesity epidemic — at least for young women — is more serious than we thought. Many young women with obesity are erroneously being deemed "normal weight" or "overweight" and therefore aren't getting appropriate health advice. And we know that obesity increases the risk of serious health problems, such as high blood pressure, high cholesterol, type 2 diabetes and heart disease.

What's your BMI? What does it mean to you?

May 08, 2010