Everyone from nutritionists to diet gurus claims that drinking lots and lots of water can help you lose weight, make your skin rosy and supple and flush toxins from your system. It's especially important, they say, because we supposedly suffer consistently from low-grade dehydration.
But is all this chug-a-lugging doing us any good?
Not really, say other health and medical experts.
There's no medical evidence that Americans are chronically dehydrated, says Dr. Robert Alpern, dean of the University of Texas Southwestern Medical School in Dallas and a kidney specialist.
Any extra water you consume doesn't flush your system or make your skin glow, but simply passes through your body as urine, Alpern says.
"Your body has a very good way of telling you when you're not drinking enough water: You get thirsty," he says. "The thirst mechanism is very sensitive. It kicks in long before there are any health problems related to dehydration."
Also, says Barbara Rolls, a nutrition professor at Penn State University, drinking water will not curb your appetite by making you feel full. In fact, she says, the thirst and hunger mechanisms are separate.
However, eating water-rich foods can help you feel satisfied when eating fewer calories, says Rolls, who's also author of the book Volumetrics Weight-Control Plan.
Water, of course, is crucial to the body. It makes up 70 percent of the body's tissues and plays a role in nearly every body function, from regulating temperature and breathing to digestion and removing waste.
But we generally get all the water we need through food, Rolls says.
Many foods, in fact, consist mostly of water. Soup, for example, is 95 percent water, she says, while fruits and vegetables range from 85 percent to 90 percent water, and meat generally is between 45 percent and 65 percent water.
In a published study, 24 healthy women had a chicken and rice casserole with a glass of water for lunch. The next day, they were given soup made with the same ingredients as the casserole. On the first day, they consumed an average of 392 calories each. The soup they had on the second day had 100 fewer calories, but the women said they felt just as full, says the study, published in 1999 in the American Journal of Clinical Nutrition.
"The premise is that, if you drink just water, it doesn't help to control hunger," Rolls says. "But when you incorporate it into foods, it helps satisfy you with fewer calories."
So how did water gain its reputation as a diet and beauty aid?
Nearly three-quarters of all Americans have heard the mantra that adults should drink eight, 8-ounce glasses of water a day, according to a study by the International Bottled Water Association. But doctors who say it's not necessary to drink that much water are baffled by the rule's origins.
"I don't think there is any physician who knows where it came from," Alpern says.
Of course, not everyone agrees that people get plenty of water through their diets.
Barbara Levine, director of the human nutrition program at Rockefeller University in Manhattan, says the typical American diet does not contain many water-rich fruits and vegetables. And too many people drink too many sodas and high-calorie beverages, she says.
Americans drink an average of six glasses of water a day, according to a survey Levine conducted for the bottled water association. Questioning 2,800 people in 14 cities, the researchers found that about 34 percent drink eight glasses a day, and fewer than 10 percent drink no water at all.
But besides water, Americans drink an abundance of caffeinated, sweetened and alcoholic beverages, the study says: 3.7 servings a day of soda or sports drinks; 3.2 servings of coffee and tea; 1.9 of juice; 1.7 of milk; and 1 serving of alcohol a day.
Drinking so many caffeinated beverages is leaving many of us dehydrated, Levine says. Caffeine acts as a diuretic, she says, causing fluid loss.
While severe dehydration can affect blood pressure, circulation, digestion and kidney function, mild dehydration can be blamed for some of the fatigue, dry skin, headaches and constipation that plague people today, she says.
"Water is so pure," Levine says. "There is nothing wrong with telling people to drink it.
"Why not encourage consumption of a beverage that does not contain sugar, caffeine or calories?" she asks. "It's a no-brainer."
But Alpern says that, while it's true caffeine is a diuretic, drinks such as soda and coffee are mostly water -- meaning the net effect is increased hydration, not the other way around.
"I would tell people to drink when they're thirsty," he says. "And, other than that, don't worry about it."
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