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BMI is a sliding scale - it's a formula that uses weight
and height to estimate body fat and gauge health risks due to carrying too much weight. The BMI is only one factor in determining
a person's health risk. A BMI in the "healthy" range does not necessarily mean that you are fit and healthy! BMI does not
take into account lean body mass or body frame.
The medical profession likes simplicity. Researchers have tested if
being overweight causes health risks, using a body mass index (BMI) of 25 kg/m2 as the definition of overweight. This is obviously
too simple, but it is a common method used in data analysis. Numerous studies have confirmed that having a body mass index
over 25 kg/m2 is associated with increased risk of disease (like diabetes, high blood pressure, heart attacks, etc), and risk
of a shortened lifespan.
It is important to point
out that this simple definition of "overweight" by medical researchers, is not representative of how people regard each other,
nor is it how a doctor would judge an individual patient, nor is it used by most nutritionists.
Furthermore,
the BMI of 25 kg/m2 definition of overweight is a "unisex" threshold, that suits neither men or women particularly well. Nevertheless,
a BMI of 25 to 29.9 is defined as "overweight" by some important institutions.
Body
Fat Percentage - Body fat percentage is the amount of adipose (fat) tissue in your body as a percentage of total body
weight. If your total body weight is 140 pounds and you have 28 pounds of fat, your body fat percentage is 20 percent.
How they relate:
In September 2000, the American Journal of Clinical Nutrition published
a study showing that body-fat percentage may be a better measure of your risk of weight-related diseases than BMI. Steven
Heymsfield, MD, director of the Obesity Research Center at St. Luke's Roosevelt Hospital in New York, and his colleagues evaluated
more than 1,600 people from diverse ethnic backgrounds. Researchers took body-fat measurements and studied how their body
fat related to disease risk.
"Many studies have related BMI to disease risk," noted Heymsfield. "What we did was correlate
body-fat percentage to BMI, allowing us to take the first big step toward linking body-fat percentage to disease risk. This
new research reveals the value of assessing body fat more directly using the latest scientific technology to measure body-fat
percentage," he added.
"If we think of BMI being a rough measure of body fatness, there are people - especially some
highly trained athletes - who are overweight but not overfat," says Heymsfield. "Likewise, there are people who are of a normal
weight according to BMI scales but who are overfat. BMI is a broad, general measure of risk. Body-fat assessment is much more specific to your actual fat content and thus provides a more accurate
picture."
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