I was doing some swimming today, and when I got out of the pool and dried off the first thing I did was to get some ice water to cool down a bit. Good stuff, there’s not much that’s as satisfying as cold water to a thirsty person on a hot day.
Ice water is at or about 0 degrees Celsius, and my insides have to hold themselves quite closely to the classical Fahrenheit value of 98.6, which is 37 Celsius. If my body were a perfectly insulated system with no way to generate heat internally, my body would warm the water up and the water would cool my body down until they reaches a equilibrium somewhere south of that 37 degrees. But this doesn’t happen, or we would die. The human body is not very tolerant of large changes in internal temperature. Therefore all other things being equal, the body has to crank up a little bit more metabolism to produce the heat required to heat that water up to the temperature of the rest of the body.
This immediately suggests a tempting diet plan, if not a very lucrative one: drink lots of cold water. Your body burns calories warming up the H2O, you lose weight without much effort. Plausible?
Well, there’s two possibilities depending on how determined/foolhardy you are. If you actually swallow ice, your body has to warm the ice from its negative temperature up to the melting point, add the substantial heat of fusion needed to turn the water from 0-degree ice to 0-degree liquid, and then finally raise the 0-degree liquid to 37 degrees. Swallowing ice sounds like a good way to choke to death and/or damage your esophagus and stomach so I would advise strongly against it. You could chew the ice if you like enormous dental bills after you wreck your teeth. For completeness though, we’ll do the math.
Let’s say you have a kilogram of ice. It’ll fill about a liter of space. Heating it from a freezer temperature of (say) -2 C requires 2060 J of energy (which is the specific heat of 1 kilogram of ice) times the temperature change, for a total of 4120 J per kilogram.
Now add in the heat of fusion: 333,000 J per kilogram. A big number, not bad.
Finally add in the heat required to get the water from 0 to 37 degrees, i.e., 37 degrees times 4,186 J per kilogram per degree, or 154,882 J per kilogram. The total is about 492,000 J/kg. What’s that in food calories? 118, for swallowing a 1 kg block of ice whole. Not bad, but certainly not worth the effort and risk of swallowing a tremendous amount of ice whole.
What about just drinking ice water? That cuts out the first two parts of the calculation, just leaving us with the 154,882 J per kilogram. And that’s 37 food calories.
37 food calories for a liter of ice water is not a lot, but it’s not trivial either. Done once or twice a day it could add up. More importantly if you drink sugared beverages you can replace the Coke with ice water and suddenly you’re close to having 300 fewer calories per drink switched.
So of course there’s no magic way to lose weight. But considering how easy drinking cold water is, I’d say it can’t hurt. And if you switch cold water for a 270 food calorie Coke, you’ve suddenly done yourself quite a bit of good.