What Is BMI?

What Is a “Body Mass Index”?

“BMI” stands for “body mass index” and is a measure of how overweight a person is. A person’s B.M.I. tells if that person is overweight and, if so, whether that person is obese. There are two ways to determine your BMI using height and weight in pounds.

One method of calculating BMI is to take your lbs and multiply them by 703. Then take your height in inches and square that number. Then divide the first number by the second number.

If you have a BMI of 25 to 30, you are considered overweight. If you have a BMI of 30 to 40, you are considered obese. If you have a BMI over 40, you are generally considered morbidly obese. Since the invention of the Body Mass Index since in the 1850s, doctors and scientists have developed their own BMI categories and tweaked the formula somewhat.

BMI Explained – Body Mass Index Example

Let’s use the above formula to come up with a BMI for a man who’s 6 ft tall. 6′ would be 72 inches and the square of 72 is 5184. If that man were 200 pounds, his weight x 703 would be 140,600. Next, you would take the 140600 and divide it by 5184, coming up with a BMI number of 27.1. This man would be considered overweight.

Next, let’s take a man who is 6 feet tall and 250 pounds. His weight x 703 would be 175,750. Divided by 5184, his BMI would be 33.9. The 6′, 250 lb man would be considered obese.

A 6′, 300 lb man would have a BMI of 40.68, making him technically “morbidly obese”. A 6′, 175 lb man, on the other hand, would have a BMI of 23.7, and would therefore be considered fit.

Alternate BMI Measurements

Another way to measure BMI would be to take your weight in pounds and multiply it by 4.88. Then take your height in feet and square it. Finally, take the first number (weight) and divide it by the second number (height), which would give you a similar BMI.

Finally, if you use the metric system (which is how BMI was first used), you would take your weight in kilograms and divide it by your height in meters squared. As you can see, the original formula was much less complicated.

Disputes Over BMI’s Usefulness

Though the BMI is simple to use and widespread, many doctors have disputed exactly how good the BMI is at measuring one’s health risks associated with weight. This is especially the case with U.S. doctors after 1998, when the U.S. chose to change its standards for the definition of “overweight” from 27.8 to 25, brining another 30 million Americans under the definition of overweight.

For instance, some studies have shown that a lower risk of heart disease in people who are slightly overweight than in those who are considered fit.

Also, experts have pointed out the rigid nature of the Body Mass Index can discount those who have naturally dense body types, or who have increased their body mass through athletic muscle weight gain and weight training. Many sports doctors prefer to measure percentage of body fat as opposed to the BMI, using test methods such as underwater weighing or skinfold measurements.

BMI is an important tool for medical insurance underwriting, because the higher one’s BMI, the more a person pays for medical insurance. At a certain BMI level, many insurers will deny coverage to a potential customer.

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