The Effects of BMI on Health
BMI, or Body Mass Index, is a measure of a person's body fat, based on a simple calculation of body weight in kilograms, divided by the square of the individual's height in meters.
It is used by health professionals around the world to determine whether a person is overweight or clinically obese. A person with a BMI equal to or over 25 is considered overweight, while an index of 30 or more is considered obese. At the opposite end of the scale, a BMI of less than 18.5 is an indication that a person is underweight. The optimum, healthy range is between 18.5 and 25.
Because BMI doesn't take any factors other than height and weight into consideration, many people argue that it is far too simplistic. A frequently quoted example of where it is likely to be misleading is with regard to muscle mass
Since muscle weighs more than fat, people who have a higher percentage of body muscle, such as athletes, could, on a strict interpretation of their body mass index, be considered obese a classification that for most professional athletes would clearly not be the case.