HYDRATION 101

No doubt about it–water is critical. In fact, it constitutes more than two-thirds of your body weight. However, you might not need to work as hard as you thought to get enough. Here are answers to the most common questions about staying hydrated.

Q: Do I really need to drink eight glasses every day?

A: No. According to a key review in the Journal of Physiology by Heinz Valtin, M.D., a hydration expert and professor emeritus at Dartmouth Medical School in Hanover, N.H., there’s no evidence to support drinking eight glasses of water each day.

So how much water do you really need? According to the Institute of Medicine of the National Academies, women should consume 91 oz. a day, and men need 125 oz.—a good deal more than the 64 oz. (8 cups) generally recommended.

Here’s the catch: We get most without heading for the tap or uncapping a bottle of Evian even once. The main reason? We get the water we need from a variety of sources, including food and other liquids.

Foods that supply a good amount of water in our diets

Virtually all food has some water in it. Natural, whole foods have the highest water content. Fruit and vegetables contain 80 to 98 percent water. Eating dense vegetables such as cucumbers, jicama, beets, carrots or celery with a meal or snack is one of the easiest ways to improve your hydration. Other fruits and vegetables, such as watermelon, broccoli and tomatoes, contain 90 percent or higher water content by weight.

“Approximately 45 to 50 percent of daily water intake comes from drinking fluids, about 35 percent from eating food and the rest from metabolism,” says Stephen Rice, M.D., Ph.D., M.P.H., a sports medicine specialist at the Jersey Shore Medical Center in Neptune, N.J.

Vegetables and fruits are the most hydrating (e.g., lettuce is 95 percent water). But we also get a lot from meat, as well as soup, juice, soda, milk and even coffee.

YOU DON’T HAVE TO DRINK PLAIN WATER TO HYDRATE.

All fluids count, as do foods that have high water content. For example:

• Oatmeal is 84 percent water.

• Low-fat milk is 90 percent water.

• Coffee is 99.5 percent water.

• Lettuce is 96 percent water.

• Tomato is 95 percent water.

• Broccoli is 89 percent water.

• Low-fat vanilla yogurt is 79 percent water.

• Ice cream is 60 percent water.

YOU CANNOT FUNCTION WITHOUT WATER.

Your body cannot survive without sufficient water, as noted by the fact that athletes die from dehydration. Water is the solvent for your biochemical reactions.

YOU NEED WATER FOR DIGESTION.

Water is required to moisten food (saliva), digest food (gastric secretions), transport nutrients to and from cells (blood), discard waste (urine), and dissipate heat (sweat). Water is a major component of the muscles and organs; about 60 percent of a male’s body weight and 50 percent of a woman’s body weight is water.

Q: How long can I go without any liquids?

A: “It depends on a myriad of factors including body size, sweat rate, amount of activity and environment,” says Douglas J. Casa, Ph.D., a professor of kinesiology at the University of Connecticut at Storrs. But just to give you some idea, according to Valtin, a person can die in one day without water in a desert but could last as long as two weeks in a hospital.

Q: If I’m thirsty, am I already dehydrated?

A: No. “You are underhydrated, not totally dehydrated. Thirst is a signal that your body would like more fluid,” says Nancy Clark, M.S., R.D., Boston-area sports nutritionist and author of Nancy Clark’s Sports Nutrition Guidebook (Human Kinetics, 2003).

Hydration is measured by blood concentration (e.g., the concentration of sodium in your blood)–the higher the concentration, the more dehydrated you are. When this concentration increases by just two percent, you get thirsty.

“Thirst is a warning mechanism, letting you know that dehydration is lurking around the corner, but to escalate to actual dehydration, the blood concentration must rise by five percent,” says Valtin.

What about “storing” water (i.e., drinking a lot before you go out and lose fluids)? “That doesn’t work,” says Valtin. “Assuming we’re healthy, all liquids we drink will be out of our bodies within a half-hour. So you can’t store up your liquids.”

Q: Are sports drinks better than water?

A: Sometimes. “Sports drinks are designed to be taken during exercise that lasts for more than an hour,” says Clark. “They are particularly helpful for athletes because they contain a little sugar to fuel the muscles and the brain, as well as a little sodium to enhance fluid absorption and retention.”

Q: Are coffee, tea and other caffeinated drinks dehydrating?

A: Absolutely not, says Casa. “They provide fluids just like any beverage. A slightly greater percentage of the ingested fluid may be urinated, but it’s still providing water.” In fact, “People who are used to drinking caffeinated beverages get accustomed to the caffeine and don’t urinate more fluid than they consume via their coffee or tea,” adds Clark.

Q: Is water an effective appetite suppressant?

A: “There’s no real evidence. However, people often mistake thirst for hunger, which means you could be eating food when you actually don’t even feel the need,” advises Clark.

How can you tell the difference? Finish a tall glass of water when you feel a snack attack coming on, and then decide if you still need some food afterward. Nevertheless, extensive research by Barbara Rolls, Ph.D., a professor of nutrition at Penn State, found that eating soup and other liquid-based foods at the beginning of a meal helps reduce hunger.

Q: Is cold water better for your body than water at room temperature?

A: No. “The reasons that cooled liquids (55 degrees Fahrenheit) are recommended for rehydrating–specifically for athletes–are several-fold, including the facts that they empty the stomach faster than room-temperature fluids, cool the body down a little and may increase the willingness to drink,” says Rice.

Q: Is it true that you can never get too much water, or any beverage for that matter?

A: According to Rice, you definitely can ingest too much water–resulting in hyponatremia (water intoxication). “This is most commonly seen in marathoners who run so slowly that they don’t generate much temperature rise or sweat yet are drinking water excessively,” says Rice.

But don’t worry. Someone who’s healthy couldn’t really get to this point, says Valtin. He estimates that it would take almost 15 liters of water for a healthy person to develop hyponatremia.

Proper Hydration During Exercise in Hot Weather

In warm weather, how can you find the energy to get outside and exercise? By using the proper hydration strategies, you can have energy to perform your best even if the weather is at its worst.

Water is an important nutrient that composes approximately 50-60 percent of our body weight. For years, we’ve been told to drink eight glasses of water a day for optimal health. But that one-size-fits-all prescription no longer fits a training athlete. Fluid intake is an important part of training and athletic performance. The benefits of adequate fluid and electrolyte intake during exercise include lower heart rate, improved blood flow to working muscles and skin, body temperature control, support for muscular contraction, preventing hyponatremia (low blood sodium levels), quick recovery, improved performance and lower perceived exertion.

Health experts have found that fluid requirements vary from person to person, and for many of us, the best way to stay adequately hydrated is to stick to a schedule. Most recreation athletes require approximately 11 to 15 cups of water daily, according to the Institute of Medicine.Several factors influence the need for water, including climate, muscle mass, physical activity, and diet. The goal of athletes is to consume enough water during sessions to maintain 100 percent fluids lost through perspiration. Sports science research conducted with many differing sports contested that in hot weather when an athlete loses even as little as 2 percent of fluids, performance may decline by as much as 10 percent.

Proper hydration is achieved during exercise by consuming fluids and electrolytes at regular intervals. During training distractions may prevent athletes from recognizing their thirst, occasionally fluids are not available precisely when thirst occurs, and by the time thirst is felt an athlete may already be dehydrated. Recommendations for hydration before, during and after exercise to ensure optimal sports performance are as follows: