Okay, after many hours of meditation I have finally cracked the Luke-eating thing.
For one: he didn't really eat. He took a bite and decided he hated it. Now, since he didn't really have a "meal" or eat more than a bite, he doesn't die.
Two, the fact that food in SW has lethal capacities is indeed demonstrated in ESB. Luke gets a major injurie i.e. his hand gets chopped off. The very same hand he used to put the spoon in his mouth. So one bite doesn't kill you, but it will lead to a major injury.
Food Theory Rules!!!