BMI and Body Fat: How Do the Two Work Together?
Weight Loss
Morgan Medeiros MSc
June 20, 2019

Difference Between BMI and Body FatIf you’ve set out on a path to lose weight, tone up, or both, you’ve likely stumbled across an age old argument: weight vs BMI vs body fat/body composition.

Which is most important, and are any a fair measure of health?

Let’s Start By Breaking Each One Down

Body Weight

Body weight simply refers to how many pounds or kilograms your body weighs period, regardless of height.

Body Composition

Body composition refers to how much of your body weight is lean mass/muscle and how much is fat mass.


BMI (derived from a calculation using your height and weight) serves as an estimate of body composition/body fatness.

For the overwhelming majority of the population, BMI is an accurate assessment tool, providing a range in which weight according to height will predict a healthy body composition.

For the average, untrained (non-professional athlete) individual, a BMI of 18.5-24.9 is appropriate and indicates that the individual likely has an appropriate weight or body composition for his/her height.

A BMI of less than 18.5 typically indicates that the individual is underweight and has less body fat than is healthy.

A BMI of greater than 24.9 typically indicates that the individual is overweight and has more body fat than is healthy.

Exceptions to the Rule

Trained athletes (professional or collegiate athletes, for example), often serve as outliers for BMI: because they have a greater degree of body mass, they can have a higher than expected BMI (exceeding 24.9) without the health risks typically associated with a high BMI.

So, if you have a high BMI, how do you know for sure whether or note your weight is appropriate?

You have a few options: first, speak with your physician. He or she will be able to assess your health and provide you with a weight appropriate for your height and individual health.

You may also opt to have your body composition tested. However, this is somewhat unreliable depending on the method you choose: calipers, bioelectrical impedance (hand sensors or sensors on scales) are oftentimes inaccurate.

DEXA and hydrostatic weighing (although potentially costly and difficult to locate) are the most effective means to measure body composition.

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