Free Calorie Burn from Cold Water?

WaterIt has been suggested that by drinking a gallon of cold water a day, you can burn an extra 150 calories.

Such statements provoke my inner skeptic so here’s the math… (sorry folks but this calls for metric).

Q: Will drinking a gallon of water burn burn 150 calories?

A: energy required = mass * change in temperature * specific heat capacity

  • 1 gallon of water = 3.785 kilograms
  • Cold water temp = 5C (estimate of course)
  • Body temp = 37C
  • Specific heat capacity for Water = 1 Kcal per kilogram

Therefore: 3.785 * (37-5) * 1 Kcal = 121 Kcal

OK close but no cigar.

To burn 150 Kcal, the starting temperature of the water needs to be… -2.6C!

Yikes! That’s a block of ice.

But perhaps they are also adding in all the legwork back and forth to the toilet.


4 thoughts on “Free Calorie Burn from Cold Water?

  1. Well, the kidneys have to pump water against a concentration gradient, which is a fancy way of saying they are trying to push water in the opposite direction of where it naturally wants to go. The laws of thermodynamics say you can’t do that without energy. So the kidneys must surely burn up a lot of calories every day. (Here’s a great post about this:

    So drinking a gallon of water (at any temperature) must surely increase your kidneys’ need for energy as it tries to keep all those precious minerals from getting flushed out with the excess water. Maybe that’s where the extra 29 calories comes from.

    On the other hand, do you want to wear your kidneys out so fast? πŸ™‚

  2. Oh and technically – sorry, but you started this geekery with your fancy metric stuff πŸ™‚ – consuming a gallon of ice would consume way more than 150 calories, because with ice you’d have a phase change, which consumes much more energy than a simple change of temperature. I think for water the value is about 80 cal/g, or 80 Kcal/kg. So to get your body to melt that ice, add another 3.785 * 80, or 302.8 Kcal, for a total of 452.8 Kcal.

    By the way, the high energy involved in a phase change explains why the ice in your drink melts faster on a humid day than on a dry one (temperature being equal) – the condensation of water vapor on your glass adds more heat energy to your drink! Neat, huh?

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