The BMI (Body Mass Index) is a simple tool used to categorize individuals as underweight, normal weight, overweight, or obese based on only two factors: height and weight. Age, gender, race, muscle mass, bone density, and overall body composition are not taken into consideration. According to the BMI, you are of normal weight if your BMI is between 18.5 and 25, overweight if it is between 25 and 30. Anybody with a BMI of 30 or more is categorized as obese.
BMI is derived from a simple math formula, BMI = weight (kg) / height2. Lambert Adolphe Jacques Quetelet, a Belgian astronomer, mathematician, statistician, and sociologist, devised it in the 1830s. When Quetelet devised the BMI formula, there were no computers, calculators, or electronic devices, so he developed a simple system. It was never designed to assess the "healthy weight'' of an individual, so it really only sort-of works at that.
And, although we now have technology that can help us add some complexity to the calculation, any one single number will still not be able to assess our overall level of health or true risk for disease.
Unfortunately, the CDC (the Centers for Disease Control and Prevention) and the NIH (the National Institutes of Health) still stand by the BMI. It is still used by many researchers, health care providers, and fitness professionals and seems to be the “gold standard” for many insurance companies. The BMI really is just a number. When considering your overall level of health and risk for disease, I recommend finding a provider that will also take into consideration your family history and a handful of other tests and measurements that together can help pull together a more complete picture for you.