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Dialysis Discussion => Dialysis: News Articles => Topic started by: okarol on February 11, 2007, 04:26:05 PM
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Weighing the value of BMI
Web Posted: 02/11/2007 05:11 PM CST
Paula Hunt
Express-News
When it comes to keeping score of your health, Body Mass Index (BMI) has become a number to watch.
You can't adopt a baby from China if you have a BMI above 40.
You can't model on the catwalks of Spain if you have a BMI below 18.
If you're somewhere in the middle, this might leave you thinking you're healthy.
Or just confused.
Derived from a calculation based on your height and weight, BMI is an estimate of how much of your body is made up of fat, or what the Centers for Disease Control calls "body fatness." Doctors, government agencies, health-care institutions and insurance companies use BMI to determine whether someone is overweight (as indicated by a BMI of 25 or more) or obese (30 and above) because it's quick and simple to use.
BMI matters because research has indicated that being overweight or obese is strongly associated with increased risk for a number of health problems: heart disease, stroke, certain cancers and diabetes. A BMI under 18.5, considered underweight, carries risks as well.
That BMI has its limitations is widely acknowledged.
BMI doesn't take into account your gender, race, family history, blood pressure, cholesterol level, physical fitness or a host of other disease risk factors. BMI relies primarily on the scale, which can't differentiate between fat and lean tissue when you stand on it.
Thus, BMI can overestimate the amount of fat on a person who carries a lot of muscle mass, like an athlete, while it can underestimate the amount of body fat on someone who has lost muscle mass through aging or illness.
Michael Parchman, an associate professor in the department of family and community medicine at the University of Texas Health Science Center, uses BMI in his practice but not as a measure of health.
"BMI is an easy-to-calculate number that allows me to explain to patients what their risk is of either having or developing some serious health problems," says Parchman. "If your BMI is high, it's like driving to work on icy streets. It doesn't mean you're going to have an accident, but your chances of having a wreck really go up compared to driving when its sunny."
There's a difference between being overweight and being overfat, says Donovan Fogt, an assistant professor in the department of health and kinesiology at the University of Texas at San Antonio.
"Overweight (is) associated with increased risk of disease, but we know that fat itself is an independent risk factor for cardiovascular disease, diabetes and other (diseases)," says Fogt. "So what we'd really like to know is percent body fat."
There are a number of different means of determining body fat percentage that are more precise than BMI, including hydrostatic (underwater) weighing, skin fold calipers and bioelectrical impedance.
Knowing your body fat percentage can be a good gauge of your weight loss or fitness program. While a scale can tell that you've lost 10 pounds, a body fat test can tell you how much fat you've lost and how much muscle you've maintained or gained.
But recent research indicates that the simplest method to determine health risk might require nothing more complicated than getting out your measuring tape.
"The most powerful predictor that we've been able to see is waist circumference," says Dr. Riva Rahl, medical director for the Cooper Wellness Program. "For men, a waist circumference of more than 40 inches and for women a waist circumference more than 35 inches is considered high risk. BMI doesn't take into account the physiologic distribution of adipose (fat) tissue."
Although waist circumference and BMI are interconnected, studies have found that measurement of central obesity — fat around the abdomen, also known as "love handles" — is a better indicator of risk for diabetes and heart disease than is BMI alone. Researchers who published a study in the April 2005 British Medical Journal found that waist circumference was a better test of insulin resistance than any other method they tried.
While BMI alone may not be the best indicator of health, experts say it's not a number you should ignore.
"BMI heightens your sensitivity to knowing if you're overweight and it's helpful if you want something to guide your progress (in losing weight)," says Rahl.
"But," cautions Rahl, "a normal BMI doesn't gives you free range to eat junk food or never exercise."
phunt@express-news.net
http://www.mysanantonio.com/salife/health/stories/MYSA021207.03C.ART0.b9015a.html