BMI vs body composition: which is which?

BMI stands for “body mass index” and is a measurement of an individual’s weight with respect to their height. It’s a basic mathematical equation that is quick and easy to calculate with just a person’s height and weight metrics, giving it accessibility and popularity within the medical community and beyond. It is not a measure of body fat—a common misconception—but it does often correlate with body fat, in that it provides insight into whether or not you’re likely to be at a healthy body weight for your height. It’s important to realize that BMI is a general indicator of health and disease risk rather than a direct measurement of a person’s body composition.

Body composition, on the other hand, specifically measures how much of an individual’s total weight comes from lean mass (muscle, bones, connective tissue, and water) and how much comes from fat. Accurately determining an individual’s body composition is generally much less accessible for most people, often requiring the use of expensive equipment and testing through a variety of methods. The clear benefit is that body composition reveals your body fat percentage, offering greater insight into your health and disease risk than BMI alone.

Body composition testing is also more insightful for a greater variety of body types, including individuals who have a healthy BMI but a higher body fat percentage (sometimes referred to as “skinny fat”), as well as those who are very muscular, who might have an unhealthy BMI but who also have a healthy body fat percentage。