If you're an Atkins fan, fill up that CamelBak. A recent University of Connecticut study suggests that athletes on high-protein diets need more water than those who load up on carbs.
U of C nutritionist Nancy Rodriguez recruited five men from the university's track team and fed them all their meals for three months. The first month, the guys ate a diet consisting of seven percent protein, the second month, 15 percent, and the final month, 30 percent-roughly equivalent to the Zone diet or a moderate Atkins plan.
As the athletes boosted their protein intake, their hydration levels dropped. Rodriguez wasn't surprised-metabolizing protein requires lots of water. "The more protein you eat, the more water you need to help the kidneys get rid of the waste," she says. The kicker: Though results showed that the men required more water when they ate the high-protein grub, none of them felt thirstier. "Thirst is not a good indicator. By the time you're thirsty, there's a good chance you're already dehydrated," Rodriguez says.
Don't despair, burger buffs. No one's insisting you ditch the patties-just be sure to chase them with plenty of fluid. Standard recommendations call for one and a half to two liters of water per day, whatever the diet, but Rodriguez advises upping that to two and half to three liters if you're getting more than 40 percent of your calories from protein. And don't dally: Rodriguez estimates that your body's water needs rise after only about a week of high-protein fare.