We've been told to drink eight glasses of water a day to keep our bodies hydrated so that the systems in our body can keep functioning properly and for us to keep doing our daily activities well. But Aaron E. Carroll, a professor of pediatrics and assistant dean for research mentoring at Indiana University School of Medicine, recently wrote in The New York Times that it's all a myth, going as far as to say that "there's no science behind it."
Aaron says that the belief originated from a 1945 Food and Nutrition Board recommendation that said people need about 2.5 liters of water daily, but ignored the statement after it: "Most of this quantity is contained in prepared foods."
He goes on to say we can hydrate ourselves with other drinks like juice, beer, tea, and even coffee (while citing this research for the case on coffee), but still points out that water is the best beverage for hydration. Aaron's beef, however, is that past studies have failed to prove a causation that drinking eight glasses of water will really result in a healthier body. And when it comes to hydration, he says "The human body is finely tuned to signal you to drink long before you are actually dehydrated," so you should be fine (unless you have a kidney problem where drinking loads of water is needed).
So should we or shouldn't we drink eight glasses of water?
The amount depends on a number of factors, like your workout and the climate. According to Patrick Joson, a triathlon coach certified by the International Triathlon Union, we need to gulp two mouthfuls of water (4 to 6 ounces of water) every 15 to 30 minutes when exercising because we lose water and salt when we sweat. It works the same way when the weather is hot: We lose water by sweating so we need to hydrate ourselves by drinking water (and yes, eight glasses or even more).
And as for food having water so we don't need to drink so much, Luz Callanta, a senior lecturer at the University of the Philippines College of Home Economics, points out that water is more important than food: "You can survive 40 days without food. But without drinking water for 2 to 3 days, you will die because of dehydration" which goes to show that the water in food isn't enough and that you really should be drinking.
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