Minecraft wiki entry for Food, associated text: Every type of food is fully renewable, except for enchanted golden apples.
It is impossible to damage another entity or break blocks directly while eating.
Brown and Red Mushrooms are the first food items to be added into the game, and used to be directly edible before the addition of Mushroom Stew.
The mushrooms were first made edible in 0.24_SURVIVAL_TEST
Besides spawning in darkness (as usual), Pigs would drop them upon death.