well, i dont think that eating really brings your high down so much as it is moreso that the passage of time doesnt seem so slow so really your just naturally coming off your high and are just consumed with the fact of eating, also i think that when you are done eating your more aware of other sensations your feeling, so the high isnt so much in your head as it was, but i do believe that it slows it some because your body is metabolising the food so some of the energy is spent on the food rather than the weed as well, there are many different explainations.