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Metabolic Rate Increases Slightly With Water Consumption

Jan. 5, 2004 -- Whether your weight-loss strategy espouses carbs with no fat or protein with few carbs, there is one thing your plan most certainly recommends -- water. From the veggie-based Ornish diet to steak-loving Atkins (and virtually all diets in between) "drink lots of water" is part of the mantra.

Now comes scientific evidence that H2O really does help you lose weight. Researchers in Germany report that water consumption increases the rate at which people burn calories. The impact is modest and the findings are preliminary, but the researchers say their study could have important implications for weight-control programs.

Eight Glasses a Day

Despite the fact that most diets call for drinking at least eight, 8-ounce glasses of water a day, few studies have been done to determine if the practice actually speeds weight loss. In an effort to answer this question, Michael Boschmann, MD, and colleagues from Berlin's Franz-Volhard Clinical Research Center tracked energy expenditures among seven men and seven women who were healthy and not overweight.

After drinking approximately 17 ounces of water, the subjects' metabolic rates -- or the rate at which calories are burned -- increased by 30% for both men and women. The increases occurred within 10 minutes of water consumption and reached a maximum after about 30 to 40 minutes.

The study also showed that the increase in metabolic rate differed in men and women. In men, burning more fat fueled the increase in metabolism, whereas in women, an increased breakdown of carbohydrates caused the increase in metabolism seen.

The researchers estimate that over the course of a year, a person who increases his water consumption by 1.5 liters a day would burn an extra 17,400 calories, for a weight loss of approximately five pounds. They note that up to 40% of the increase in calorie burning is caused by the body's attempt to heat the ingested water. The findings are reported in the December issue of The Journal of Clinical Endocrinology and Metabolism.

"Very, Very Small Effect"

The researchers write that up to 70% of the increase in metabolism, "cannot be attributed to the heating of the ingested water," but exercise physiologist Daniel Moser, PhD, tells WebMD that it is unclear from this small study if this is the case.

"Larger studies are clearly needed to confirm this extremely modest weight-loss effect," he tells WebMD.

Nutritionist and American Dietetic Association spokeswoman Leslie Bonci, MPH-RD, says even if the findings are confirmed the clinical implications are slight.

"Obviously people are looking for ways to increase metabolism, but this is an very, very, small effect," she tells WebMD. "We are talking about just a few calories a day."

Bonci says the standard weight-loss plan dictates encouraging people to drink more water stems from the belief that the liquid fills the gut to make people feel fuller.

"Some plans say that drinking water flushes fat out of your system, which is absolutely ridiculous," she says.

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