While
fats can not be used to replenish muscle tissue, that's a
moot point: carbohydrates and
fats aren't just fuels — a lot of them go towards rebuilding the body (
fat, for example, is in part used to form brain tissue, myelin, bile, bone marrow, and various cellular organelles — all of which are things that you use up to allow your body to exercise and to recover from it).