Monday, January 29, 2007

BMI is a Joke when Measuring Obesity

Seriously, what was the government thinking? I cannot believe all the money they spent on this only to come up with such a flawed formula for measuring obesity.

BMI is a calculation derived from your height and weight. Per the government, there is a set guideline for how much a person should weigh based on their height. So why is BMI flawed you ask? BMI does not take into consideration deviations in the human body. It does not factor in someone with a big bone structure versus someone with a small bone structure. It does not factor in how bone mass lessens with age. It does not factor in how much muscle mass someone has. A professional football player with next to no body fat would be considered morbidly obese because of how much he weighs (which is really due to muscle, not fat).

The government needs to wake up and learn that body fat percentage is a much more accurate way to determine whether or not people are obese. Not just any body fat test will do, but the hydrostatic water tank method (the most accurate of all) should be the gold standard.

What is hydrostatic body fat testing? Bone, muscle, and connective tissue, (collectively known as lean mass) sinks, while body fat floats, is the premise behind hydrostatic testing. By figuring out your land weight and water weight (based on buoyancy), a computer program calculates your body fat as a percentage of your total weight. This type of body fat testing is based on the Archimedes principle which states "when a body is submerged under water, there is a buoyant counter force equal to the weight of the water which is displaced". Since bone and muscle are denser than water, a person with a larger percentage of lean body mass will weigh more in the water and have a lower body fat percentage versus someone with less lean muscle mass. A person with more body fat will make the body lighter in water and will have a higher percentage of body fat.

Yes hydrostatic testing is more difficult (price, time, availability, etc) than punching in a few numbers in some BMI calculator, but no one ever said the truth was easy.