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Doing the math on BMI is worth the effort

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Are you or your children part of the obesity epidemic?

Is there really an obesity epidemic or is this just a new scare tactic used by health officials to coerce you into a more healthy lifestyle?

Maybe the answer is a little bit of all of the above.

There's no question that the weight of Americans has grown over the previous 50 years. Some say it's a natural result of more and more prosperity, while others point toward increasingly unhealthy lifestyles and burgeoning appetites for not-so-healthy foods. 

Whatever you blame it on, we Americans are definitely heavier than our parents and grandparents and that should, rightfully, alarm us. Although the percentage of adults who are considered merely overweight for their height has changed little between 1960 and 2006 (31.5 percent versus 32.7 percent), the percentage of adults who are considered obese or extremely obese has risen dramatically.

Surveys by the National Health and Nutrition Examination Survey dating back from 2006 to 1960-1962 utilize a Body Mass Index quotient of body measurements — height and weight — to categorize people within normal, overweight, obese or extremely obese groups. A BMI number is the result of dividing a person's weight by twice their height in inches squared and the result multiplied by 703. 

For example, if you weigh 170 pounds and are 6' tall (72"), then your BMI is 170 divided by 5,184, with the result (.0328) multiplied by 703, which equals a BMI of 23. 

The BMI categories for each weight status are:

• Below 18.5 - underweight

• 18.5 - 24.9 - normal

• 25.0 - 29.9 - overweight

• 30.0 - 39.9 - obese

• 40.0 and above - extremely obese

So, a BMI of 23 is in the normal weight range. 

BMI for adults and children, regardless of sex, are computed the same way. It's a relatively simple measure, one that's important to roughly gauge someone's weight category without either precise measurements or more extensive body fat measurements.

But it's far from perfect. Clearly, it is just a rough indicator tool to tell people and their health care providers when people are entering an at-risk weight class for their height. It doesn't account for the unique physiological differences inherent among individuals or between sexes. 

You could be a "thick" body type. You could be "big boned." You could be wider than another person that's your same height. You could just be a heavier body type that's perfectly healthy — muscle does weigh more than fat.

You could also successfully argue that BMI does not account for the differences in body fat between men and women.

Body fat content measurements, whether calculated through specific trunk and appendage measurements or through actual pinch or weightless environment measurements, are considered a more effective manner of determining a weight class and their appropriate health risks. It also accounts for the different body types of men and women.

Among the six classes of body fat groups, a body fat of 10 percent or less for men or 17 percent or less for women is categorized as athlete, while an individual is in the overfat category if a man's body fat reaches 25 percent or a woman's reaches 29 percent. Obese for women is 35 percent or more, while 25 percent is the threshold for men.

The problem with body fat measurement is that it's a bit more complicated and not readily available to most of the general public. The military services use it and medical facilities utilize it for more precise calculation of actual body fat and condition. But, by and large BMI has become a standard measurement for weight classes in America.

The BMI is an important number since organizations like the Centers for Disease Control and many others describe BMI as "a reliable indicator of body fatness for most people and is used to screen for weight categories that may lead to health problems."

The BMI also lets us look at simple trends and that's where we get numbers that show American adults (ages 20 and older) in the simple overweight category (BMI 25.0-29.9) have stayed about the same, the rate of those rated obese (BMI 30.0-39.9) has more than doubled from 15 percent to 34.3 percent since 1980. The extremely obese category (above BMI 39.9) has sky-rocketed from .9 percent in 1980 to 5.9 percent in 2006.

This isn't just about feeling like your weight is normal. A BMI is much more useful for its potential to improve your health.

Those whose BMI places them in overweight and obese categories are higher at risk of diseases like hypertension, Type 2 diabetes, heart disease and stroke. Gallbladder disease, sleep apnea and even some cancers are more prevalent in people who fall into those categories.

A BMI in those categories should, at the very least, trigger you to speak to a medical professional about your health, as well as cause you to reassess your lifestyle with the intent of reducing your BMI and the associated health risks. 

The BMI of your children should also be of concern. That number may not be the only factor in determining whether your child is heading down an unhealthy path, but it's an important one to pay attention to. 

It's not perfect, but we should all use BMI as an indicator, not as a final measurement. It should not, for example, serve as a diagnostic device to determine a specific health condition. 

And, clearly, a low BMI doesn't guarantee you are healthy.

Rather BMI should be considered a big red caution flag that simply tells us we're moving in the wrong direction and that we'd better do something about it.

Oh, and if you're concerned about the math, Google "BMI calculator" and choose from a plethora of easy sites that will do the math for you.

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