Drink two glasses of water and burn 23 kcal extra
You can lose weight by drinking ordinary tap water, according to researchers at the University Medicine Berlin. In the Journal of Clinical Endocrinology & Metabolism they describe how after drinking two glasses of water the body's level of energy expenditure increases. The effect is probably due to the fact that the body has to invest energy in absorbing water.
Water & calories
That the body burns more energy after drinking water was already known. The same researchers published the results of a study which showed that drinking six glasses of water made men burn more fat, and women more carbohydrates. [J Clin Endocrinol Metab. 2003 Dec;88(12):6015-9.] In that study the researchers got their test subjects to drink half a litre of water. If you extrapolate the figures from their study – and assume there's nothing wrong with this – then you could lose an extra 2.4 kg body fat in a year by drinking 6 glasses extra water daily.
The question is: how is this possible? A small part of the effect is due to the temperature of the water. Water is colder than body temperature; so warming up the water costs the body some energy. Another part of the effect could be to do with the extension of the stomach. A full stomach activates nerve paths, and as a result the concentration in the blood of pep hormones, such as adrenalin and noradrenalin, increases. Because adrenalin causes cells to work harder, the amount of energy expenditure also increases slightly.
In the study referred to here, the researchers gave their test subjects – 8 fat women and 8 fat men – 0.5 litre water on one occasion, on another 50 ml water, and on the third occasion 0.5 litre water containing a little salt. The salt solution was iso-osmotic, meaning that the salt concentration was the same as in the blood.
The body doesn't just absorb water. When you drink water, it only enters your bloodstream once it contains the same amount of salt as your blood does. So when water enters your stomach, the body first gets salt from somewhere, which it mixes with the water you've drunk until the right salt concentration is reached. That's why isotonic thirst quenchers work better than ordinary sports drinks.
The graph below shows the effect that the 3 different drinks had on the body’s energy expenditure [EE] over a period of 90 minutes.
The figure below shows the effect on total energy expenditure for all test subjects. It is clear that the increase in energy expenditure disappears when the test subjects were given a salt solution to drink. That means that the stomach extension is not so important for the energy enhancing effect.
Getting salt to the stomach after drinking half a litre of water is what costs the body energy, the researchers suspect. That is apparently what caused the increase in energy expenditure.
The first author of the study, Michael Boschmann, works for Forum Trinkwasser. Forum Trinkwasser is an organisation of German drinking water companies, whose aim is to improve the image of drinking water. Forum Trinkwasser also financed Boschmann's study.
If you're thinking of experimenting with an increase in your water intake, don't forget that it is possible to overdose, even on something as apparently harmless as water. Water poisoning is not a rare phenomenon. Just ask Wikipedia. It may sound crazy, but people die every year from drinking too much water.
J Clin Endocrinol Metab. 2007 Aug; 92(8): 3334-7.
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Water & Hydration