The term comfort food refers to any food or drink to which one habitually turns for temporary respite, security, or special reward. The reasons that something becomes a comfort food are diverse but include the food's familiarity, simplicity, and/or pleasant associations. Small children often seem to latch on to a specific food or drink (in a way similar to a security blanket) and will repeatedly request it in high stress situations. Adults, however, are certainly not exempt.
A substantial majority of comfort foods are composed largely of simple or complex carbohydrate, such as sugar, rice, refined wheat, and so on. It has been postulated that such foods induce an opiate-like effect in the brain, which may account for their soothing nature.
The term comfort food was added to the Webster's Dictionary in 1972.

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http://en.wikipedia.org/wiki/Comfort_food