The theory is, that in order to absorb ice cold water, it has to be warmed by the body to body temperature. I just don't buy that warming ice water to body temperature can use enough calories to make a difference. Its just my opinion, but corp is right, I have read that before too.
I don't think it would be the same for cold food, for this reason.
Water is absorbed by the stomach where food is digested. Water doesn't have to be digested to be used by the body like food. Stomach acids will go to work on the food before it can be warmed up. Im no physiology (sp?) expert though.