Two reasons. One is that the muscles have degenerated again, and the density of fat meat has decreased.

The second is that during exercise, the basal metabolism of the body becomes higher, that is to say. Doing nothing, the body will consume more calories than before fitness. Therefore, the energy absorption rate will be high during fitness. Now suddenly stop, the energy absorption rate is low, and then it will lead to weight loss.

I can't say the second reason, probably related to these factors. I don't quite understand how to say it.