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Thursday, August 27, 2009

Skeptical About BMI

Skeptical About BMI
Body Mass Index or BMI has become the standard indicator used by health professionals to determine if a person is too fat or not. Basically, using only height and weight as input variables, a BMI number is produced. If a person has a Body Mass Index number of between 18.5 and 24.9 you are of a health body weight. If you have a number higher than this and you are overweight, below this and you are underweight. The formula for calculating BMI in standard units is as follows:

In 1998 the US National Institute for Health decided to lower the cut off number for being overweight to a BMI of 25.0, previously it was 27.0. This one move effectivly redefined 30 million Americans as overweight. Unfortunately this has made a bad indicator of weight, even worse. Actually, BMI was never intended for use as a health indicator. It was developed in the 1850's as a way to decide if people fit in to mesomorphic, endomorphic, or ectomorphic body classification types. This quakery indicated that peoples personality was determined by their body type as well. With endomorphs(fat) being Jovial, and Ectomorphs(skinny) being intellectual.

By far the largest flaw that BMI has, is the fact that doesn’t distinguish between body fat, and muscular mass. For example a 5’ 6”, well built bodybuilder weighing 190 lbs would be classified as “obese”. While a 6’ 2” ectomorph with toothpick arms and legs, and a pot belly, who happens to weight 160 lbs, would be classified as “ideal” weight. In reality our short weight lifter only has 10% body fat, and exercises very regularly. While our pot bellied geek only exercises virtually on a x-box, and possess a whopping 18% body fat, because he has no muscle mass.

If you would like to calculate your own BMI click this link:

For an interesting exercise, continue to lower the weight you enter in the calculator for your height, until you find out at what weight you would be considered "too skinny" according to the BMI. If your like me you will find the number absurdly, and unhealthily low!

Why does care about an innacurate fatness index? The answer is simple. By pushing this easily dismissed standard for body weight, we simply provide the obesity denial crowd an easy way to dismiss weight loss all together. When the “fat excuse” crowd points out the obvious practical fallacy of BMI, they can in turn stretch their argument that the “fat crisis” in the United States is a fabrication of the diet industry and their friends the drug makers. How can we argue against this rather appearent observation. These same “fat acceptance” types will go on to further conclude that we should forgo dieting altogether since it is unhealthy and destined to fail or worse yet cause anorexia. By not acknowledging the obviouse about BMI we run the danger of legitimizing the irresponsible behavior of the “fat excusers”.
Skin fold caliber tests provide a more accurate way to measure body fat compostition, but they are impractical for every day use, and can be difficult to get consistent results from. But once you master it you can get the most accurate picture of your body fat percentage

Here is an economical skinfold caliper I own and use

Another very usuable, and more accurate gauge of body fat is the Hip to Waist ratio. This indicator uses the ratio of the circumferances of a persons waist versus the circumferance of their hips to determine if they care carrying weight in a fashion that may be unhealthy.

You can caluculate your Waist to Hip ratio at this link:

If someone has a high BMI number, of over 30 (which is the World Health Organization’s cutoff), they more than likely have a weight issue. Since most females lack the ability to gain large muscle mass it is probably a better indicator of body composition women. Frankly if you aren’t doing deadlifts, squats, and drinking protien powder shakes and your BMI is high, you probably do have a weight issue. We all should be carefull not to fall into the denial path that the “fat acceptance” crowd has set up for us. But it is important as well to fully understand what BMI is and how it is calculated before we formulate a weight loss or fitness plan around it

1 comment:

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