BMI not a good measure of healthy body weight, researchers argue

When it comes to defining obesity, one size does not fit all, say a pair of University of Pennsylvania physicians and obesity researchers in an editorial published in the journal Science.

Body Mass Index, or BMI, is widely known as the standard measure for differentiating those who are of normal weight and those who are obese. A BMI of 18.5 to 24.9 is considered normal, a BMI of 25 to 29.9 is overweight, and a BMI greater than 30 is obese. But the researchers find that BMI is not an accurate measure of fat.

People with a BMI measure higher than 30 are generally thought to be at an increased risk of heart disease, diabetes, cancer, and more.

Tanya Lewis of LiveScience.com reports:

Yet several recent studies suggest that in some cases, a high BMI could actually protect a person from dying of heart failure, kidney failure and other chronic diseases. When someone has a chronic illness, having more fat could possibly provide additional energy reserves. And in some cases, a low BMI may be a result of a person having an illness.  

Co-authors of the editorial, Dr. Rexford Ahima and Dr. Mitchell Lazar, share why BMI does not properly explain the causes of poor health:

For one thing, BMI doesn't take into account fat, and it doesn't indicate where fat is distributed on the body. Belly fat (fat around the abdominal organs) increases the risk of diabetes, heart disease and death, whereas peripheral fat (fat beneath the skin elsewhere in the body) may be more innocuous, studies suggest. BMI also fails to account for differences in race, gender, age genetics and starting weight. For most people, BMI provides a "reasonable measure" of body fat, but is not accurate for athletes (who weigh more because of muscle) or older people who have lost height, said Ahima.

So why does the medical community still rely so heavily on BMI as a predictor for future health woes? According to Ahima, solely because it's a simple measurement. Subsequently, the researchers are calling for better ways to assess individual health prospects.

The pair write that "there is an urgent need for accurate, practical, and affordable tools for assessing body composition, adipose hormones, myokines, cytokines and other biomarkers as predictive tools" in order to allow physicians to separate the fat-but-fit from those in danger.

Read the full article at LiveScience.com.