First and foremost, it's not a good idea to only eat one kind of food. To survive, we need 20 amino acids—of which nine are essential, meaning we can't make them ourselves and must get them from food—as well as a plethora of minerals and vitamins. (And, obviously, we need water in addition to food to keep our cells hydrated so they don't wither and stop functioning.) Throughout history we've often combined foods, like rice and beans, yogurt and nuts, and even macaroni and cheese to a certain extent, in an attempt, or by accident, to intake the proper balance of nutrients that you usually can't attain from eating a single food item. But in times of famine, fasting, or strange double-dog-dares, there are a couple of foods a human could survive on...at least for awhile.