Being Normal or Obese is All in the Measuring

In spite of one study that says those who are a bit overweight might live longer than those who are “normal weight,” you still need to know where you stand – are you within your healthy weight range, overweight or obese? What that now-famous study published in the Journal of the American Medical Association failed to discuss was quality-of-life issues, including any diseases you might be living with during this longer life span. That’s why it’s critical to know your weight status. Many of us believe we can simply look in the mirror or jump on a scale, but that’s just not the case.

“A large proportion of overweight individuals do not have an accurate perception of their weight status,” said Marney A. White, an obesity researcher at the Yale University School of Medicine Eating Disorders Research Program who co-wrote a study in Obesity Research. “This underscores the need for measurement of obesity. People in the overweight range who don’t know it may not make the effort to manage their weight. As a result, they may be at heightened risk for developing obesity and associated health problems.”

Dr. White’s study suggests a substantial proportion of Americans incorrectly perceive their weight status. More than half of all men reported they were normal weight when they were, in fact, overweight; almost 20 percent of men who thought they were normal weight were obese. About 25 percent of women who thought they were normal weight were overweight, and 10 percent who thought they were normal weight were obese.

Another study in Obesity Research showed that even physicians have trouble determining their status. About half of the overweight physicians thought they were fine.

Is Body Mass Index the perfect tool to predict whether you’re at increased health risk from being overweight or obese? Not exactly. The problem is that BMI, based on your weight and height, doesn’t distinguish between muscle mass and body fat. In other words, two people can have the same BMI but very different percentages of fat.

For example, a bodybuilder with lots of muscle and low body fat might have the same BMI as a person who has more fat and less muscle. Highly trained athletes typically have low body fat and more lean body mass and therefore cannot be defined by standards based on the average community.

Despite this drawback, BMI is used because it’s cheap and easy. More exact body fat measurements are costly and inconvenient. In fact, the Centers for Disease Control and Prevention state: “BMI is one of the best methods for population assessment of overweight and obesity. It is low-cost and easy to use.”

BMI is used to determine health risk factors related to obesity.

“It correctly predicts if someone is overweight or obese approximately 80 percent of the time. It’s considered a surrogate measure of obesity,” said Arlette Perry, a professor of exercise and sport sciences at the University of Miami. It is not particularly effective with athletes or the elderly, she added, but as long as you are aware of that, BMI can be a valuable tool.

Here’s how to calculate your BMI:

Take your weight in pounds and multiply by 703. Then divide this by your height in inches, and then divide that by your height in inches again.

Or you can r use a BMI calculator at http://nhlbisupport.com/bmi/ bmicalc.htm.

Here is the breakdown for adults older than 20:

Below 18.5: Underweight

18.5-24.9: Normal

25.0-29.9: Overweight

30.0 and above: Obese

MANY EXPERTS SAY your body fat percentage is a more important indicator than BMI for disease prediction. The best ways to measure body fat include: underwater weighing, bioelectrical impedance, dual energy X-ray absorptiometry (or DEXA, which measures the density of your bones), computerized topography or calipers (skin-fold measurements). These methods, however, are expensive, might not be readily available to the public or in general clinical settings and need to be administered by highly trained personnel.

Here is how to evaluate your body fat percentage, according to the American Council on Exercise:

Essential fat

Women: 10-12 percent; Men: 2-4 percent

Athletes

Women: 14-20 percent; Men: 6-13 percent

Fit

Women: 21-24 percent; Men: 14-17 percent

Acceptable

Women: 25-31 percent; Men: 18-25 percent

Obese

Women: 32 percent-plus; Men: 26 percent-plus

There are body fat scales that are relatively accurate and inexpensive. One of the best ones is the Taylor Body Fat Analyzer Bathroom Scale (Model 5553, about $35), rated best by both Good Housekeeping and Consumer Reports.

What about waist size? A recent study completed at the Johns Hopkins Bloomberg School of Public Health and published in the American Journal of Clinical Nutrition looked at more than 27,000 participants and reported that waist size might be a better indicator of health risk than BMI. The study showed that a waist of more than 40 inches for adult men or 35 inches for adult women puts them at risk for type 2 diabetes.

CHARLES STUART PLATKIN IS A NUTRITION AND PUBLIC HEALTH ADVOCATE AND THE AUTHOR OF BREAKING THE PATTERN (PLUME, 2005) AND THE AUTOMATIC DIET (HUDSON STREET PRESS, 2005). COPYRIGHT 2005 BY CHARLES STUART PLATKIN. WRITE TO INFO@THEDIETDETECTIVE.COM.