Fat Mass Index vs Body Fat Percentage

While body fat percentage is more informative than body mass index (BMI) because it distinguishes fat from muscle, it can also be misleading because it is dependent on lean (or fat-free) mass.

Fat mass index (FMI) has an advantage over body fat percentage because it is not influenced by lean mass.

For example, if a person is low in muscle, then this can artificially inflate their body fat percentage even though they might have a low or normal amount of fat mass. This is referred to as “skinny fat” when a person has normal or low body weight but has a higher body fat percentage. FMI can help further distinguish the degree of “skinny fat.”

On the flip side, if a person is high in muscle mass then their body fat percentage could be lower even if they have excess and unhealthy levels of fat. In this case, FMI can identify excess fat when body fat percentage fails.

Some studies even show FMI as a better screening tool for predicting the presence of metabolic syndrome than body fat percentage and BMI in men and women.