> your body may respond by only burning 4 instead of burning its usual 5 Absolutely. In fact your body will repsond and burn less (because you weigh less). So

> your body may respond by only burning 4 instead of burning its usual 5 Absolutely. In fact your body will repsond and burn less (because you weigh less). So what that means is this is an iterative process. Put 4 in your body and watch how much you're burning. If you're now burning less than 4, put 3 in your body. Now watch how much you're burning. If you're now burning less than 3, put 2 in your body. It's an ongoing process of re-evaluation and adjustment, and every body is different. But they are very much the same in the one way that science limits to universe. If you put in less energy than you use, your body can't invent that extra energy it needs to function, and therefore your body must start to consume it's energy reserves. It's not possible for anything else to happen.