I don't think that is why they give it although I have heard people saying that. I know that it is given to AIDS patients for many reasons but for actual muscle wasting (a bigtime AIDS symptom) they use test. But you know, ime, prednisone is one of those things that is overused in medicine and I'm sure many times it is used for reasons outside it's actual effectiveness.
It is a corticosteroid and so it is related to the effects of cortisol in your body. In fact it causes adrenal suppression after a while. And also it is given in cases of adrenal insufficiency. Basically to replace a lack of cortisol in the body. So of course cortisol has to do with protein metabolism but we know what excess cortisol does to muscle. People on pred get fat, not muscular
I had someone say to me that they "request" pridnisone every year for their sinus problems and I was like WTF?!
I worked as a vet tech and it is used for dogs a bunch. They tend to handle it well compared to people. But how would we know?
It definitely does bloat your face, etc like you said. The second time I went on it the side effects were so bad I couldn't even continue taking it. Some people with really bad auto-immune conditions (I have had sarcoidosis) that can't be controlled any other way end up being on pred long-term and it's really a case where the drug itself is slowly killing them but there is no other choice. It causes adrenal shutdown so that is why it has to be tapered off at the end. And that depends on the length of time you've been on it. Going off pred abruptly can be deadly.
But when it is needed it can be a life saver.