The quality of fast food is pretty good actually, the preparation of it is horrible though. So much stuff is fried in fats. You eat a fast food meal and you're looking at 700-2000 calories after burger, fries, coke, onion rings, apple pies, hot fudge sundays, shakes, supersizes, etc. And you eat it all in 5-15 minutes usually. This stuff is all goin in to digestive tract. Well your body basically puts blood supply priority to your digestive system, so other places like your skeletal muscles get less blood. It's a good reason you shoudn't excersize after eating a heavy meal, basically why your mommy told you to not swim for an hour after eating. So naturally your parasympathetic system kicks and your sympathetic (aka adrenaline/fight/flight stuff) is toned down. So you are going to hit that food coma. I'm sure when you are not eating fast food you are eating much less fat and less calories at a time so this isn't as pronounced.
