It’s true that when you drink ice water, your body uses energy (calories) to raise the liquid’s temperature to body temperature. But not very much.
Roger Clemens, DrPH (doctor of public health) in nutrition and biological chemistry, and associate director of regulatory science at the USC School of Pharmacy, walked us through the math. For the sake of simplicity, he didn’t take thermodynamics into account, which would change the numbers very slightly.
You have an 8-ounce glass of ice-cold water in front of you. That’s about 240 grams of water.
When you drink the ice water, which is roughly 4 degrees Celsius, your body will expend calories to bring it to body temperature, which is about 37.5 degrees Celsius; that’s a difference of 33.5 degrees. To raise 1 gram of water 1 degree Celsius, 1 calorie is expended. (This is a “little” calorie—what scientists use to measure small units of energy. The calories we refer to colloquially are actually 1,000 of these and are known as kilocalories in the science world.)
Raising 240 grams of water by 33.5 degrees Celsius will take 33.5 calories x 240 grams of water, which equals 8,040 little calories.
Dividing 8,040 by 1,000 gives us 8.04 food calories (kilocalories). Therefore, you’ll burn about 8 calories for each glass of iced calorie-free beverage you drink. That’s equal to about one Life Saver: not exactly a weight-loss miracle.
Using Clemens’s figures, it would take about 435 8-ounce glasses of ice water to lose a pound.
And do we have to tell you? Consuming large quantities of cold water can have serious health effects, such as an overall lowering of body temperature, a decrease in the functionality of the gastrointestinal tract, and, in extreme cases, anemia. Drinking a lot of water can also lead to water intoxication.