gaining weight....
Someone used to joke that since the universe neither allows matter to be created or destroyed then if someone loses some body fat it goes to another person as weight gain.
Transcendental dieting.
Nah. It goes down the commode, where eventually, it comes back to us as purified water or compost/topsoil/worm food, etc. An old-fashioned outhouse with area wildlife probably does it a whole lot better, but not as purty.