Discordance Between Body Mass Index (BMI) and a Novel Body Composition Change Index (BCCI) as Outcome Measures in Weight Change Interventions.

Objective: A general assumption is that the body mass index (BMI) reflects changes in fat mass (FM). However, it fails to distinguish the type of weight that is lost or gained-fat mass (FM) or fat-free mass (FFM). The BMI treats both changes the same although they have opposite health consequences.