An ex-girlfriend of mine used to nag me about my caffeine intake (which really was far from bad) because, “It dehydrates you.” I argued that any coffee or carbonated beverage with caffeine was largely… umm… water. “You’re telling me that the caffeine in my Coke not only completely obliterates the 11oz. of water in the can, but also saps existing water from me like a parasite? Bullshit.”
Turns out I was correct.
One Comment
I always wondered about this also. I did finally find out that caffeine keeps you from effectively concentrating your urine when you are slightly dehydrated already. If you are trying to determine whether you are dehydrated by the color of your urine, you could be deceived because your pee is more clear (more water = less concentrated = less yellow) with caffeine than it would be without it. So it’s easier to make the mistake and think that you are more hydrated than you really are. Shouldn’t make a difference in ordinary life, but if you are running or racing you want to perform your best.