Drinking water appears to help weight loss. How?

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My blog focused yesterday on a study reported at the American Chemical Society annual meeting, which links the eating of berries with the potential for brain ‘de-ageing’. Another study reported at this meeting that caught my attention, partly as a result of the fact that it was widely reported in the press, was one that appears to show that drinking more water facilitates weight loss.

Like the berry study, we don’t have many details to go on. But it seems that a bunch of people were put on a low-calorie diet for 12 weeks. Half of these were instructed to drink 16 fluid ounces (1 pint/437 mls) of water prior to each of their meals. The other half were not instructed to do this. The group drinking the water lost an average of 15 lbs, compared with 15.5 lbs, compared to an average of 11 pounds in the other group. I’m assuming from the way that this study has been reported that the difference was statistically significant.

If it was, what’s the explanation for this phenomenon? The obvious explanation is that individuals who drink water before a meal eat less during the meal. As a report of this study states here, previous work has found that individuals drinking water before a meal do tend to eat less during it. I don’t doubt that this effect might indeed help promote weight loss.

However, is it the only possible explanation for this phenomenon? As I reported here last year, there is some evidence that enhanced hydration might actually promote weight loss through helping maintain the metabolism, and also by helping cells give up their fat.

It has been found that cells that are dehydrated do not take up glucose very efficiently [1] – something that could cause the metabolism to stall. Also, studies show that when the blood is made more dilute, fatty breakdown in the body (lipolysis) is enhanced [2,3]. This evidence suggests that there is some support for the notion that keeping well hydrated can assist in our quest to shed fat.

And then another thought occurs – time and time again I see people who hydrate themselves properly report enhanced energy. This in itself might be a sign of improved metabolism. But even if it isn’t, I think it would be fair to speculate that individuals will tend to move a bit more if they have a bit more energy. This, in theory at least, might contribute to the weight loss effects of drinking more water.

For information on how to maintain adequate hydration, particularly in the heat, see this recent post.


1. Thornton SN, et al. Hydration increases cell metabolism. International Journal of Obesity [epub ahead of print publication 20 January 2009] Int J Obes (Lond) 2009;33(3):385

2. Mathai ML, et al. Selective reduction in body fat mass and plasma leptin induced by angiotensin-converting enzyme inhibition in rats. Int J Obes (Lond) 2008;32:1576″1584.

3. Schliess F, et al. Cell hydration and mTOR-dependent signalling. Acta Physiol (Oxf) 2006;187: 223-229.

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