Thread: Conservation of mass in a human body

Hi. I have been pondering how a human body loses mass from exercising but instead encountered a weird thought.
We often exercise in order to lose weight. When we exercise, stored chemical energy in fats are converted to mechanical energy. However, this conversion of energy does not equate to loss in mass, i.e. mass is conserved. Of course in reality we do lose weight but this is because of the excretion of water and salts. A good practice is to replace our water loss and salts after exercise. So that means exercise more does not result in weight loss!? The only time we loss mass substantially is when we defaecate.. So I should defaecate more instead of exercising to loss weight??

But essentially, the often quoted "burn fat to lose weight" is wrong since mass is conserved during energy conversion! (Except nuclear fission/fusion)

Muscle weighs more than fat per unit area, and helps change the body's metabolism such that it burns fats more readily. You lose mass as a general rule, but it's more about how the body changes how it uses energy... or, more appropriately, how it stores it and for how long.