Myth No. 1: We need to drink at least eight 8-ounce glasses of water a day
Researchers aren't sure where this familiar advice came from, but most agree there's very little solid scientific evidence to support it. The average adult loses only about 1 liter of water a day through sweating and other bodily processes -- the equivalent of only four 8-ounce glasses. We typically get that much water just in the foods we eat. Drinking an additional eight tall glasses of H20 is probably more fluid than most of us need.
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"People who drank less than four glasses of water a day were no more likely to show signs of dehydration than those who drank six or more," says Lindeman. "We found absolutely no difference between those who drank a little and those who drank a lot when we looked at all the standard markers for dehydration."
Myth No. 2: Caffeinated beverages make you dehydrated
"For years, newspaper and magazine articles have repeated the notion that caffeine is dehydrating as if it's absolute fact," says University of Nebraska researcher Ann Grandjean, EdD. But in a study published in the October 2000 Journal of the American College of Nutrition, Grandjean and her colleagues at the Center for Human Nutrition showed that it's pure fantasy.
The researchers looked at how different combinations of water, coffee, and caffeinated colas affected hydration levels in a group of 18 men between the ages of 24 and 39. During one phase of the experiment, the only fluid the volunteers consumed was water. During another, 75% of their intake was caffeinated.
"Using almost every test ever devised to measure dehydration, we found no difference at all," says Grandjean.