What is Body Mass Index?
Body mass index (BMI), is a numerical measurement that compares an individual’s weight to his or her height. Body mass index does not measure the percentage of total fat in the body, but it does help to estimate what an appropriate weight should be for a person’s specific height. The BMI calculation is quite easy to figure, and helps to identify if a person is of average weight, overweight, or underweight. The concept was first developed in 1830 by a Belgian scientist, Adolphe Quetelet, and is generally calculated by taking a person’s body weight, and then dividing it by the square of his or her height (kg/m2, lbs. x 703/inches2, or lbs. x 4.88/ft2).
Body mass index calculations became quite popular in the early 1950s as western cultures began to become increasingly overweight. This tool was a very simple way to determine an individual level of thinness or fatness and allowed physicians to make personalized recommendations. While the BMI can be quite useful, some have found fault with the calculation due to variances in height. Taller individuals found that their BMI was quite high when their actual body fat levels were not. This was due to the fact that those with a taller height were not simply scaled up to account for the difference; their BMI basically doubled instead of remaining proportionate to their weight.
Current body mass index levels are as follows: optimal weight allows a BMI of 18.5 to 25, levels under 18.5 are considered to be underweight, while levels above 25 are considered to be overweight. A BMI level of under 17.5 is considered to be grossly underweight and may indicate an eating disorder, malnutrition, or other medical condition. BMI levels over 30 are considered to be obese, and a BMI of over 40 is considered to be morbidly obese.
Because body mass index only factors in a person’s height and weight, it makes naive conclusions about that person’s general health condition. The BMI does not take into account the distribution of muscle or bone mass, and does not classify the fat level. Body mass index commonly overestimates the fat composite levels in individuals with high amounts of lean body mass, such as athletes, and frequently underestimates the fat composite levels in individuals with low amounts of lean body mass, such as the elderly. While BMI has a few shortcomings, it is still considered to be a valuable tool to gauge a person’s fitness level. This index should, however, be just one of many evaluation practices used to determine overall health.
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