BMI is NOT TMI

BMI vs. Body Fat Percent

Ok, this is something that’s bothered me for a while and I just wanted to clear the air a bit.  The terms body mass index (BMI) and body fat percentage are both used to classify people as normal, overweight and obese.  However, there is a clear difference in the way these two terms are used to analyze a person’s body weight and composition and therefore should not be used interchangeably. 

BMI is just a ratio of a person’s mass (in kilograms) to their height (in meters²) or kg/m² and as a result doesn’t give any information about a person’s body composition.  This measurement should only really be used for the general population and more specifically those who are sedentary because it doesn’t incorporate any information about a person’s actual body composition, specifically muscle mass.  According to this measurement bodybuilders and athletes, who typically have very low levels of body fat, are classified as overweight or in some instances obese.  This happens because they generally have large amounts of muscle mass and because BMI is just a ratio of weight to height, a larger muscle mass will increase their body weight while leaving the height unchanged and as a result the ratio is increased.

On the other hand, a body fat percentage is a more accurate measurement of a person’s actually body composition and should be used to classify a person as overweight or not.  This will give you very specific information about how much body fat and lean mass (fat free mass) a person has.  That’s why body fat percentages should be used as the standard for classifying people as overweight or not.

I do realize that a BMI is a lot easier and quicker to attain because all you need is a person’s height and weight instead of equipment needed to measure body fat percentage but if at all possible try to use the latter!