After he stopped his diet, paul found that he gained back more weight than he lost. this is probably because he decreased his resting metabolic rate increased his resting metabolic rate gained muscle mass he stopped exercising

Probably because he stopped exercising

It's a common mistake that people do in their diet plan. Exercise burn calories, so if someone suddenly stop his/her exercise without lowering their calories intake, they will gain weight. The key for a good body is watching your calories and nutrients intake. If you don't want to get fat without exercising, then simply dont eat too much