This is just a question out of curiosity, but it's been niggling at my mind for a while. Why does the body break down muscle before it burns fat when fat is its secondary source of energy.
In a famine, which is what the body thinks it is when you go into starvation, wouldn't you need muscles to carry on looking for food? Or is it just a case of your body trying to keep you alive for as long as possible regardless of how it does so? Sorry if this has been asked before, I didn't quite know how to search for it...
Based on what I know about energy metabolism (I could be wrong!), the first thing that goes is your blood sugar - it's use up to fuel your muscles. When that's gone (and you haven't fainted) your liver kicks in and releases glycogen. This is then turned into glucose for that to be taken up by your muscles. After that, your fat storage is depleted and finally your muscles. This is because muscles are much harder to break down than fat is, since they are made of protein/amino acids rather than fat.
Thus, in a famine, this is why you see the skinniest of children. However, most of them have been starved for so long that they've lost their muscles too.
Hope this helps!
Actually, (I heard this on Fitness Rocks, it's a podcast by Dr. Monte Ladner and he takes scientific papers and reviews them, as well as talking to some of the people who did the research) the body breaks down muscle first because it is much easier to break down muscle. Fat is only used as a last resort. I don't remember the biology behind it though. But, that is why it is very important to do weights along with cardio, so you at least maintain whatever muscle you have.
It doesnt break down muscle before it uses fat as an energy source, Its a simples question but probably not a simple answer I'll start and someone else will probably finish it, strangely enough the body can make fat out of sugar but it can't reverse the process so when your body is in caloric deficit and can't provide sufficient glucose to maintain proper vital functioning, your muscles are degraded back into amino acids to be turned into glucose in the liver, but only after the glycogen stores are depleted, also while in caloric deficit metabolic hormones are higher and anabolic hormones are lower which makes building muscle very hard, proteins and amino acids are also very inefficient at yielding energy so it take quite a bit of muscle to provide enough glucose in times of need,
I always thought that the reason the body breaks down muscle first is because muscle requires the most amount of calories to maintain (meaning: muscle burns more calories than fat even when you're simply at rest). Therefore, if your body thinks you are going into starvation, it would get rid of what is using up the most fuel first.
I could be completely wrong though.
This has much more detailed information.
Thanks all! I've had my question quite thoroughly answered, I think!
Muscles go first too because they are made of protein which is better than fat when you are starving.