for life style change, seemingly he put up a lot of weight in the years of 1810 - 12 (some very few years of no campaigning) and he expolded when he was at Elba.

It is kind of being a full time athlete and then stopping exercise without adjusting your food intake.

This is for me the most likely explanation, as his second marriage - other eating habits - as a metabolic disorder aside, depression could also be an option, in 1814 at Elba.