While I can state countless reasons why before AND after can be viable options, exercising (regardless of when), is paramount. Now, it talking with catabolism, exercising AFTER you eat a well-planned meal is the way to go. Ideally, eating small meals every 2.5-3 hrs is the proper way to go, so exercising before/after that time-frame is somewhat irrelevant.

For those overweight/obese, exercising upon waking up, prior to your first meal is great. For those who are slightly overweight/normal, you should eat something when you wake up prior to exercise.