Defintion of Food

Food - is any substance, usually composed primarily of carbohydrates, fats, water and/or proteins, that can be eaten or drunk by an animal for nutrition or pleasure. Items considered food may be derived from plants, animals or other categories such as fungus or fermented products like alcohol. Although many human cultures sought food items through hunting and gathering, today most cultures use farming, ranching, and fishing, with hunting, foraging and other methods of a local nature included but playing a minor role.
(from http://en.wikipedia.org/wiki/Food#Food_sources)