Someone once said the BMI was a little thing some mathematician came up with but with no intention of applying it to health care. It does sound plausible. I used to train women in a gym and they'd all come complaining about gaining weight but being able to wear smaller sizes after a few months at our gym. I'd tell them to stop looking at the scales and just rely on body measurements and their clothes. Muscle is really important for women because its responsible for our metabolism and bone health. We start losing muscle after the age of 30 so it makes sense to build as much of it as possible.