Body Mass Index
What is BMI and why should I care?
BMI is the common acronym given to Body Mass Index
, a number calculated from your weight and height that roughly correlates to the percentage of your total weight that comes from fat, as opposed to muscle, bone or organ. The higher a person's BMI, the higher the percentage of fat in their body. If your BMI is under 20, you might be underweight. Between 20 and 25, you are probably at a good healthy weight for your height. A BMI over 25 is considered overweight, and over 35 is considered obese.
Charts and calculators to determine your BMI are easily
found on most health and diet sites. Of course, these
calculators are rough translations of true percentages,
and there are a number of factors that might influence
whether or not your BMI is a true reflection of your
total body fat.
For instance, muscle is denser than fat and takes up
less space. Therefore a heavily muscled person might
weigh more than a same sized over-weight person, or
two individuals with identical BMI might have widely
different percent body fat. In this case, calculating
your percent body-fat might require more sophisticated
equipment, such as an immersion tank. Since fat is more
buoyant than muscle, two same-weight individuals will
not float at the same level if they have different percentages
of body fat.
Women typically carry more subcutaneous fat than men
do, particularly in the breast and hips, so their percent
body fat may be higher without it necessarily being
reflected in their BMI or having any adverse health
effects. Very low body fat, which may or may not show
up in a BMI, depending on the individual's musculature,
might be unhealthy as well. Your body needs some stores
of fat to draw upon for energy and if fat is absent,
the body will begin to consume muscle mass to keep itself
going. Athletes who overtrain may find themselves losing
strength rather than gaining strength, for instance.
BMI, for all its approximation, is a good tool to use
in determining whether you need to lose weight, gain
weight, or congratulate yourself for being just right.