How Reliable Is BMI As An Indicator Of Good Health And Fitness?

For a while now, BMI or the Body Mass Index has been the gold standard for indicating a person’s fitness and body fat levels.

A number of BMI calculators such as this one from the NY Times require you to fill in your current height and weight based on which your BMI will be calculated.

A BMI result of below 18.5 is considered underweight, between 18.5 and 24.9 is normal; 25 to 29.9 is considered over weight and a BMI of over 30 is considered overweight.

However, is this standard reliable? Does it apply equally to all? According to several experts, there are several problems relating to this standard of calculation:

  • The BMI calculator is not able to differentiate between fat and muscle, it calculates based only on absolute terms of height and weight. The formula presumes a sedentary lifestyle and a high body fat percentage and low muscle mass.
  • The BMI formula is supposed to apply to the ‘average man’ or the ‘average woman’. However, it does not take into account that the average man or woman may have a very wide range of physical features. For instance, there may be a lot of difference between two individuals based on factors such as body buildup, bone structure, the genetic tendency of the person to create muscle or horde fat etc.
  • BMI may be a reliable indicator for the health and fitness levels of a sedentary person, but a person such as an athlete or a bodybuilder who has a lot of muscle mass will wrongly be classified as overweight or obese when the BM index is relied upon.
  • BMI is also an unreliable indicator for those of advanced age who would typically have lost a lot of their muscle mass. So here typically a person may have high percentage of body fat which is calculated (erroneously) as being of normal weight when in fact the low muscle mass could mean that the person is overweight.
  • The formula ignores waist size, which is an excellent indicator of the state of a person’s good health and risk from obesity related disease.
  • The BMI formula was developed by a Belgian mathematician called Adolphe Quetelet and not by a physician. Though it is a formula that sounds scientific it is not universally reliable.

So though BMI is useful to an extent, it is not to be considered an absolute indicator of a person’s fitness and overall health.