Most obesity research relies on the measure of body mass index (BMI, a measure of weight by height), but this does not tell us much about what really matters—how much muscle versus body fat we have, and where the fat is stored. Fat stored in the limbs (subcutaneously, so under the skin but not in the muscle) is different and maybe even protective, while fat stored deep inside, in the belly, liver, or muscles, is the real underlying threat.
