I can say for myself, based on no scientific evidence, other than having lived in my body for 32 years, that I can't eat protein before a workout. It screws me up big time (nausea, cramps, etc). I can do a little fat (never tried anything other than peanut butter, so anything truly heavy would probably be out) and I'm totally fine on simple carbs (fruit) or starches like bread/pretzels/etc.

I can, on occasion, hit some light cardio in a fasted state after waking up. It isn't preferred and I have a lot less steam than I do if I eat something roughly an hour before I work out. I can't eat less than an hour before I lift or it makes me sick to my stomach.