Rethinking Body Mass Index (BMI) for Assessing Cancer Risk

Of minimal value, if any.

A study by researchers at Albert Einstein College of Medicine of Yeshiva University suggests that body mass index (BMI) -- the most commonly used weight-for-height formula for estimating fatness -- may not be the best measure for estimating disease risk, and particularly the risk of certain types of cancer.

The study was published today in the online edition of the American Journal of Epidemiology.

BMI is calculated by dividing a person's weight (in kilograms) by his or her height in meters squared, or W/H2. Most of the early studies that used the formula, starting roughly sixty years ago, were conducted among middle-aged men. BMI has become the most widely-used weight-for-height index in large population studies of children and adults, thanks mainly to its ease of calculation and the ready availability of weight and height data. Newer technologies have since been developed for measuring body fat, but they can be prohibitively expensive and time consuming.

A BMI between 18.5 and 24.9 is considered ideal; obesity is defined as a BMI of 30 or greater. According to the Centers for Disease Control and Prevention, the higher one's BMI, the greater the risk for a range of diseases, including heart disease, high blood pressure, type 2 diabetes and certain cancers.

"It has long been recognized that BMI is an imperfect indicator of body fat because weight does not distinguish between lean body mass (muscle, bones, blood, water) and fat mass," said lead author Geoffrey C. Kabat, Ph.D., senior epidemiologist in the department of epidemiology & population health at Einstein. "This means that two individuals can have the same BMI but can have very different percentage of body fat." Furthermore, when using weight and height data, a single BMI formula may not be appropriate for all populations and all diseases."

BMI is an excellent indicator.

It is accessible to all.

It gives the proper general picture and trend.

Virtually all people with elevated BMIs are too fat. Very few are that muscular.

It is not perfect.

Nothing is.