If you eat 500 calories and burn 600 calories, the energy has to come from somewhere. So in a sense it is actually a pretty simple physics problem.
It gets tricky because calculating calorie consumption is really hard (how much of what you ate was actually turned into energy) and calculating calorie expenditure is probably even harder.
It gets tricky because calculating calorie consumption is really hard (how much of what you ate was actually turned into energy) and calculating calorie expenditure is probably even harder.