A frequently used index to assess a person's body composition (or amount of body fat) is called the body mass index, or BMI. This assessment compares your body weight to your height to come up with a value that indicates whether you are underweight, normal weight, overweight, or obese.
Understanding your body composition is valuable because a person's level of body fat is directly correlated with health outcomes. Obesity-related diseases include heart disease, type 2 diabetes, hypertension, and stroke. Thus, working toward weight loss if you are overweight or obese can have a profound positive effect on your health.
The table above provides established BMI norms based on various categories of health and fitness.
For most people, BMI is a quick and easy way to assess body composition, which is why it is so commonly used. However, since body weight (and not percent body fat) is used in determining BMI, there may be problems when using BMI to assess people who are heavily muscled (such as body builders) or who have an athletic body type. Because muscle weighs more than fat, those who have well-developed muscles typically appear overweight or obese according to the BMI reference chart. If you are a person with an athletic or muscular build, do not use BMI as the only method to assess your body composition. An estimation of body fat using the skinfold method would be a more accurate choice.