I read recently in a magazine that you can lose weight just by drinking cold beverages, since your body has to burn calories in order to warm the liquid up to body temperature. Is that true?
The short answer is 'yes, perhaps', the longer answer is 'not very effectively'.
To start, we need to understand that the word 'calorie' has two distinct but related meanings:
- in science a calorie, or gram calorie, is the amount of energy needed to warm one gram of water by one degree Celsius*.
- a dietary calorie, or kCal, is a measure of the energy contained in food and is equivalent to the amount of energy needed to warm one liter of water by one degree Celsius, or the same as 1,000 gram calories.
So, suppose you were to drink a cup of ice water. One cup of water weighs close to 236.6 grams. Ice water is 0°C and the average normal body temperature is around 37°C, so your body will spend about 236.6 X 37 = 8,754.2 gram calories, or just short of 9 dietary calories to bring the water up to body temperature.
Because you need to burn off about 3,500 calories to lose a pound of fat, at 9 dietary calories per glass, you would need to drink about 389 glasses of ice water to make a one pound difference in your weight. If you believe the dictum that you should drink 8 cups of water a day and you made them all ice cold, then you would lose one pound every 48 days by drinking eight cups of ice water each day.
The idea that your body would burn calories to warm the water is based on an untrue assumption that your body is a closed system, not affected by outside conditions. External conditions may also influence the results. For instance, in the summer, when your body is trying to shed heat to keep cool anyway, the actual benefit of drinking cold water may be reduced.
If you choose to drink unsweetened ice tea instead of water, it contains 2 dietary calories per cup so the time to lose one pound would go from 48 days to 63. If you add a teaspoon of sugar to your iced tea, then the balance reverses. One teaspoon of sugar has 16 dietary calories, plus the two from the ice tea itself, means that you would end up gaining a pound every 48 days.
To put this all into another context, if you were to walk at the leisurely pace of 2 miles per hour for one hour, you would burn up an additional 164 dietary calories, the equivalent of 18 glasses of ice water. Nine dietary calories would burn off in just 3.3 minutes of walking. One bagged potato chip, what the British call 'crisps' as opposed to french fries, has just about exactly 9 dietary calories (160 kCal per 17 chips) and so eating 8 fewer chips would have the same effect as drinking 8 cups of ice water. Having a hamburger made with ¼ pound of ground beef instead of a ⅓ pound could save 90 dietary calories, which is more than you burn up from drinking 8 cups of ice water the day.
Bottom line - it might work but there are far more immediate and effective ways to lose weight than drinking ice water, or as the marketers say, "as part of a healthy lifestyle, including a balanced diet and exercise, drinking ice water can help you lose weight", with the emphasis, of course, on the healthy lifestyle, including a balanced diet and exercise.
* Since the initial definition of calorie was created centuries ago, the science part has become so exacting that there are now multiple refinements on the term, but for this purpose the above definition is completely adequate.
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