WEIGH SMART

Practically everyone has done it.

Walking by the scale in the bathroom, the urge to weigh yourself overcomes you and you (regretfully) step on.

The little wheel spins to reveal a number bigger than you'd like, and depression ensues.

Ed Jones, assistant director for wellness and fitness at Binghamton (N.Y.) University, says some people who closely monitor their weight can end up doing more damage to themselves than good.

"Weight is a real emotional issue," Jones says. "A scale is a great thing if you put it into perspective."

You may be a healthy weight for your body, and a simple bathroom scale can't tell you that. So before you start fretting that the scale doesn't match up with what you think you should weigh, it's best to find out what the numbers should be for your age, height and fitness level.

There are several methods for determining if you are a healthy weight. First, see your doctor. Your doctor would have the best handle on what weight you should be according to your height and your health history, which includes your family health history.

Weight and height charts may work for children, but they are less accurate for adults, Jones says.

Body Mass Index is a better indicator of healthy weight. It is an equation that takes into account height and weight, and spits out a number that can be used to measure appropriate weight. There are some scales that can be programmed to give Body Mass Index instead of weight, and dozens of Web sites are set up to calculate it for you.

To calculate Body Mass Index on your own, multiply your weight in pounds by .45. Then, multiply your height in inches by .0254 and square the result. Divide the pounds answer by the inches to get your Body Mass Index.

If your Body Mass Index lands in the healthy range, 18.5 to 24.9, according to the National Institutes of Health, you're probably fine, right? Wrong.

Some unhealthy people may fall inside the healthy range because they have little muscle and a lot of fat. Fat weighs less than muscle. Likewise, some healthy people may not fall inside the healthy range because they have a lot of muscle and little fat.

Ratios indicate risk

Waist-to-hip ratios may tell more about a person's health. To calculate your ratio, measure around the smallest part of your waist with a tape measure. Then, measure around the largest part of your hips. Divide the waist measurement by the hip measurement.

According to the National Institutes of Health, women with waist-to-hip ratios of more than 0.8 or men with waist-to-hip ratios of more than 1.0 are "apples." They are at increased health risk because of their fat distribution.

For men, the ratio should be less than 1.0, and women's should be less than 0.8. The National Institutes of Health says those who have ratios higher than that may have an increased risk for diabetes, heart disease and hypertension.

In addition to where a person carries his weight, body fat percentages have been associated with heightened health risks, Jones says.

New technology has made it possible for people to measure their body fat percentages at home. Scales that double as body fat monitors tell percentages without the poking and prodding of the skin fold method, and without the water and expensive equipment of the immersion method.

The scales use technology called bio-electrical impedance to measure body fat. It works by sending a small electrical signal through the body, measuring resistance to it by various tissues.

The signal, which cannot be felt by the user, is slowed by fat tissues, which contain only 20 percent water. It determines body fat percentage by how fast the signal travels from one foot through the body to the other foot. It also takes into account sex, age (in some cases), height, weight and fitness level.

The scale is a little more expensive than a regular scale, but it is small and portable. The process is quick and non-invasive. However, it doesn't always work accurately, admits the company that makes the scale.

Not all body fat scales have the ability to calculate percentages for professional athletes, children or very obese people. Nylons interfere with conductivity, and dehydration can affect the result. Badly calloused feet also may change the answer. People with pacemakers should not use the monitor.

Given that the body fat monitor has been shown to be within 5 percent accurate compared to a new, expensive and relatively accurate X-ray method, the monitor is an easier option. Keep in mind the most accurate method of measuring body fat is an autopsy, not a very appealing option.

Don't obsess

People can fall into the same trap with body fat monitors as they do with scales. Don't continuously check your body fat percentage. It changes even slower than weight. Jones suggested checking it no more frequently than every two or three weeks, being as consistent with time and day as possible.

Jones says men and women should have different goals for body fat because their bodies require different amounts of fat. According to Shape Up America, a national initiative to promote healthy weight and increased physical activity in America, a healthy body fat percentage for women between the ages of 18 and 39 is 21 to 32. Men the same age should have between 8 and 19 percent body fat.

For women between the ages of 40 and 59, a healthy body fat percentage falls between 23 and 33 percent, while men the same age are between 11 and 21 percent, according to Shape Up America. Between 60 and 79 years old, a health body fat percentage for women is 24 and 35 percent. Men are between 13 and 24 percent.

"Weight is a real emotional issue. A scale is a great thing if you put it into perspective."

Ed Jones, Binghamton University