Subject: Does the human body ever 'burn' muscle for energy?

     There is a prevalent concept that if a human does not ingest a minimum number of calories in a 
given day, that their body will, "go into starvation mode." When people say this, they usually mean that 
your body will begin to burn muscle, regardless of the amount of fat available to burn.

     From my personal experience, I was able to build muscle and lose fat simultaneously while eating a 
calorie restricted diet. Exercising four days a week, I’d burn an estimated 1,000 calories on those days. 
On exercise days, I’d eat 1,600 calories. On two of my three non-exercise days I’d eat 800 calories. And 
on the other non-exercise day, I’d eat only 160 calories.

     My understanding is that muscle, being different from a lipid cell, does not “store” energy the way 
that fat does. Thus, your body will never “burn” muscle for sustenance. Instead, it uses energy and 
nutrition to build muscle, and if muscle isn’t being continuously built, it begins to diminish. Would it be 
more correct to say that there are both a “Calorie Cycle,” and a, “Nutrient Cycle?” Humans burn calories 
to provide energy for action, but specific portions of humans are “made” from specific nutrients. All 
nutrients contain calories, but not all nutrients are identical. So, as long as you eat enough food to 
maintain a healthy “Nutrient Cycle” and exercise well to continue replenishing your muscles, then if 
you’re operating under a calorie deficiency, you’ll only lose fat.

     Is any of this correct?

Re: Does the human body ever 'burn' muscle for energy?