Does caffeine dehydrate you? Is water the best fluid to drink to rehydrate?

Here is a series of interesting questions and answers put to Penny L. Wilson, dietitian and nutritionist at the Memorial Hermann Ironman Sports Medicine Institute*.

THE MYTH: Caffeine dehydrates you.

THE TRUTH: Caffeine is helpful for sports performance, but it is also a diuretic, isn't it? Not exactly. Recent research shows that caffeine doses of between 250 and 300 milligrams (about 2 cups of coffee) cause a minimal increase in the urge to urinate about 3 hours after they are taken. But the study also explains that exercise seems to cancel out this effect. If you run within 1 or 2 hours of drinking coffee, the amount of urine does not increase. During exercise, blood flow tends to be concentrated towards the muscles and away from the kidneys, so urine production is not affected. Moreover, if you usually have a caffè latte in the morning or an espresso at lunch, your body gets used to caffeine and the effect on both your psychological state and your performance is minimal.

Energen 30 ml is the single-dose energy gel based on maltodextrins that also contains 50 mg of caffeine. Alternatively, for those who want an energy supplement with maltodextrins only, we have Maltovis.

THE MYTH: There is nothing better than water for rehydrating.

THE TRUTH: Although water is an excellent means of hydration, in some situations it may not be the best choice. For an easy one-hour run on a cool day, sipping water is perfectly fine. But if you are doing a 15 km run on a hot morning and your sweat is salty (there are white streaks of salt on your face or clothes after the run), you also need to take in some sodium. Salt helps you retain water and makes it harder to lose through urine. A sports drink or an electrolyte-enhanced water (see Isodrink) are excellent choices, whereas taking high doses of salt before the run is not. There is no way to pre-load sodium and avoid losing it. Whatever is not used is eliminated in the urine.