I highly doubt the two calories or so used to heat water would effectively replace gym time. It takes what, one calorie to heat one gram of water by 1 degree C? So a glass of ice cold water, to heat to body temp, would take ~20 calories. A body, even at rest, is constantly generating heat. The energy used to heat the water would have been lost by the body in other ways if the water hadn’t been consumed. The only way that it would increase calorie expenditure is if the combined temperature increase of the volume of water was enough to consume all of the heat that the body is losing plus a bit more. You then burn the “bit more” calories as a bonus.
I highly doubt the two calories or so used to heat water would effectively replace gym time. It takes what, one calorie to heat one gram of water by 1 degree C? So a glass of ice cold water, to heat to body temp, would take ~20 calories. A body, even at rest, is constantly generating heat. The energy used to heat the water would have been lost by the body in other ways if the water hadn’t been consumed. The only way that it would increase calorie expenditure is if the combined temperature increase of the volume of water was enough to consume all of the heat that the body is losing plus a bit more. You then burn the “bit more” calories as a bonus.
http://message.snopes.com/showthread.php?t=20027