Thursday, March 23, 2006

Wondering about Watering

Back when I pretended to run indoor track for about half a season in high school (before I realized that of all the running sports indoor track is by far the worst), someone on the team told me that if you drink too much water too soon after you run you don't absorb it, you just pee it all out. You have to drink it slower over a longer time period to actually absorb it. That seemed to make sense to me... When you drink a liter or two of water it does seem like you pee it all out pretty quickly.

But then about three weeks ago I actually stopped and thought about it. The water you drink enters your gastrointestinal tract (i.e. stomach, intestines, etc) whereas the urine you produce is a result of filtration of your blood. So really, for the water to get from your GI tract out through your urinary system it definitely has to be absorbed. Not to be too gross about this, but if that whole absorption theory were true you'd actually poop out the water. Gross.

So then I thought about it some more and came up with this... Maybe it means that most of the water is absorbed through the large colon into the bloodstream where the increase in blood volume turns off the ADH in the collecting ducts of the kidney allowing you to excrete the excess free water. Likely there isn't enough time for redistribution of the fluid throughout the intracellular and extracellular spaces since derangements in overall blood volume would be correctly quite rapidly.

Yeah. That makes more sense. So to some extent the "non absorption" theory probably is true, just not in the way I'd been thinking about it all these years.


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