I'm curious about the maximum rate of fat loss (not weight loss) and how the body works. For the sake of argument, what is the rate of fat loss if one ate nothing at all? I recall that it's about a pound a day. But if a pound of fat stores about 3500 calories, I don't see how the body is going to burn that much in a day's time unless one is exercising like crazy, also. A very strict calorie-reduction diet might result in losing 3-4 pounds a week if a lot of exercise is thrown into the mix. (My wife attained this some years back on a low-calorie, high-exercise program).

Do my numbers appear accurate? (And again, my caveat is that I am not advocating eating nothing. I have to add it, since someone is going to think I'm doing it).

There has been a little bit of research in this area, and as I recall there is a maximum amount of energy one can get from their fat cells in a given day. Exactly what that amount is I can't recall but the more fat one has the more energy they can get.

The energy needs of the body will be met so when required the body will break down muscle for energy. In a true starvation situation, when one is not eating anything, muscle is broken down fairly quickly as there are parts of the body (primarily CNS) that can only run on glucose which is created from broken down muscle.

Interesting though. The pound a day may be "weight" loss and not "fat" loss - which would better correspond with what John explained - that in starvation you will also break down muscle for energy.

Your BMR/RMR is the number of calories that your body needs just to exist.

Let's say it's 2000 calories. So, if you lay in bed all day, if you eat 2000 calories and your body burns 2000 calories processing that food/breathing/thinking/whatever, then you will maintain your weight.

If you move around that increases the calories that you're burning -- that's why some people exercise a lot -- and if you're not eating the calories your burning, then you'll lose weight.

JohnP is right that there is only so much energy that the body can take from fat -- muscle (protein) is easier to break down. But initially, it's the glucose that's stored in your muscle and liver that will get used up first. When that isn't there anymore, it'll turn to other sources of fuel -- some of it will be fat, some of it will be muscle.

Simple and easy read: http://forecast.diabetes.org/magazin...teins-and-fats

Thus, the advice that you can see on these boards and others is to exercise not to lose weight, but rather to keep the muscle. If muscle is being used, then the body is consuming the glucose stored there and if the cells are empty, then when you eat, they will fill up again, rather than turning into fat (storage).