Food in your stomach can make a huge difference in how long it takes to peak, ex, 45 minutes to roll, or 2 hours if you've eaten. Not sure about how much it effects total absorption... I say in most cases it's best to have eaten something. If not only because it helps prevent stomach discomfort (like pain killers do to me), than sometimes it's good to have food in you just to keep you up and running during your drug experience which may eliminate your appetite for a long time despite your bodies need for energy. The only thing I really take without food in me are benzos because they are easy on the stomach and when ya need em, you want em to work as fast as possible... well, that and pot-food haha