Dehydration

As we enter to hot days of summer, it is even more important to be aware of your fluid intake.  We live in a place that gives us access to some of the best terrain for surfing, mountain biking, trail running, etc. Exercising in the heat increases the risk of dehydration and we need to be aware of this as we play in this amazing terrain.  Remember when the only guideline for staying hydrated during exercise was to drink–and drink often? And plain water took the podium as the perfect sports drink? Thanks to new insights on how our bodies process fluids and other nutrients while we’re working up a sweat, the conventional wisdom on when and what to drink is evolving. And although the rules may have changed, the objective remains the same: improved performance and optimal health.

Here’s a look at the old and new views on hydration.

Old: Drink ahead of your thirst.

New: Drink according to your thirst.

For years, sports nutrition experts advised athletes to drink “ahead of thirst,” that is, to drink before getting thirsty and more frequently than what thirst dictated during exercise. Experts warned that by the time you feel thirsty, you’ve already become dehydrated. However, recent studies show that being in this state of slight dehydration has no negative impact on performance or health.

For example, in a study from the Sports Science Institute of South Africa, runners did three two-hour workouts while drinking a sports drink at three different rates: by thirst (roughly 13 oz. per hour), at a moderate rate (about four oz. every 15 to 20 minutes), and at a high rate (about 10 oz. every 15 to 20 minutes).

The study found no significant differences in core body temperature (rising body temperature hastens dehydration) or finishing times among the three trials. However, during the high-rate trial two of the eight runners suffered severe stomach distress and couldn’t finish the workout, suggesting that drinking too much too often can cause problems.

“The idea that thirst comes too late is a marketing ploy of the sports-drink industry,” says Tim Noakes, M.D., a professor of sport and exercise science at the University of Cape Town, South Africa. While thirst is not a perfect indicator of hydration status, it does appear to be a good indicator of the optimal drinking rate during exercise, according to Noakes. “The answer is just drink as your thirst dictates.”

Old: Aim to completely prevent dehydration.

New: Aim to slow dehydration.

You’ve probably been told to drink enough fluid during exercise to completely make up for what you lose through sweat. In other words, the goal is to weigh the same before and after your workout. But the latest research has revealed three problems with this advice.

First, when athletes drink according to thirst, they usually replace only 60 to 70 percent of the fluid they lose, but studies have shown that this state of slight dehydration does not harm performance or health.

Second, the recommendation to drink enough fluid to prevent weight-loss is based on the false assumption that all the weight lost is from body fluid evaporating as sweat. However, recent studies show that a significant amount (as much as 60 percent) is actually due to the loss of water stored with fat and carbohydrate molecules, which is released from the muscles when these stores are converted to energy. Although it contributes to sweat and weight loss during exercise, this kind of fluid loss has no dehydrating effect because it doesn’t reduce blood volume.

Third, the problem with drinking to completely prevent dehydration is that it tends to dilute the concentration of sodium and other electrolytes in the blood, especially during prolonged exercise of more than two hours. Electrolytes are dissolved minerals that regulate your body’s fluids, helping create the electrical impulses essential to physical activity. When you sweat, you release more sodium than any other electrolyte. Since even the most electrolyte-packed sports drink has a lower sodium concentration than sweat, when you replace sweat with a sports drink you essentially water down your blood. In extreme cases, blood sodium dilution leads to Hyponatremia, a potentially fatal condition where fluid balance is thrown off to the point where cells literally become waterlogged, causing the brain to swell.

Therefore, instead of drinking to completely replace the fluid you sweat out during exercise, aim for keeping thirst at bay. Respond to your thirst right away with small amounts of sports drink, but don’t allow your thirst to build to the point that you’re forced to guzzle down a full bottle at one time. Taking a few sips about every 10 to 12 minutes will help you stay hydrated and avoid stomach upset.

Yours in Health,
Cody
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