Hi, my name is Massimo, my wife Cinzia has MG. I'm lurking here for a while.
I know how hard it is to be in a good shape on prednisone. I can tell you our experience hoping it might be usefull to you.
Cinzia finded out she has MG in 2004 since then she's on prednisone. We came across a diet "the zone diet" that is supposed to contrast some of the side effects of prednisone and so far is being very effective. We use it has a "base" replacing all the Industrial products with fresh foods.
My wife is not obsessed with the diet. We are human beings an we need to pamper ourselves with a dessert or a pizza from time to time and being on an diet during the week days helps us to enjoy them more.