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Updating Hydration Information

September 29, 2005 03:02 PM

By Amanda Carlson, Nutrition Manager and Research Coordinator, Athletes’ Performance, and Jim Brown, Ph.D., Editor, Sports Performance Journal

No matter how much information is available to athletes, parents of athletes, coaches, and trainers, there are always issues that need to be emphasized, updated, or re-visited. In this column, we look at replacing fluids with foods, the mixed evidence on caffeinated drinks, and hydration for children who are tennis players, athletes, or serious exercisers.

Replacing Fluids With Food
Drinking enough water to offset the fluids lost through perspiration, evaporation, feces, and urine can be difficult for some young tennis players. Juices, sports drinks, some soft drinks, tea and coffee, and low-fat milk are all acceptable fluid-replacement choices, depending the intensity level and timing of subsequent workouts or athletic events.

But there is also the food alternative. The fluid that players need doesn’t have to come exclusively in the form of water or other drinks. Every mouthful of food contains water, and there are some foods that contribute significant amounts of water to your diet. These foods, especially fruits and vegetables, supplement fluid intake and supply other nutrients. Below is a list of foods and their approximate percentages of water.

  • apples, 84 percent
  • bananas, 75
  • blueberries, 85
  • cabbage, 92
  • cantaloupe, 89
  • carrots, 88
  • celery, 95
  • cucumbers, 95
  • grapefruit, 91
  • grapes, 81
  • iceberg lettuce, 98
  • oranges, 86
  • peaches, 88
  • pears, 84
  • spinach, 91
  • squash, 93
  • tomatoes, 94
  • watermelons, 91

Just a reminder --- drink 16 ounces of fluid in the two hours before your workout, take 4-6 gulps every 10 - 15 minutes during training or competition, and drink 16 ounces of fluid for every pound lost during your training session (base this by weighing yourself before and after the session).

Caffeine and Hydration
There is mixed evidence in the literature regarding caffeine and hydration. In a review article published in the International Journal of Sport Nutrition and Exercise Metabolism, researcher Lawrence E. Armstrong, University of Connecticut, found that caffeine may not be as dehydrating as once thought. In fact, he concluded that caffeine is no more a diuretic than water. Armstrong’s analysis of the scientific literature focused on moderate amounts of caffeine (equal to one to four cups of coffee a day). Following are some of his findings.

** When consuming a caffeinated beverage, the body retains some of the fluid.
** Moderate caffeine consumption causes a mild diuresis very similar to that of water. Water, when consumed in large volume, increases urine output.
** A person who regularly consumes caffeine has a higher tolerance to the diuretic effect.
** There is no evidence that consumption of caffeinated beverages causes a fluid-electrolyte imbalance that is detrimental to health or exercise performance.

Hydration Guidelines for Active Children
Children produce less perspiration than adults and have less ability to move heat away from the core of the body to the skin. As a consequence, they generate a disproportionate amount of heat during exercise. Chris Rosenbloom, PhD, RD, a sports nutritionist at Georgia State University in Atlanta, offers the following guidelines for hydrating younger athletes.

** Children 6-12: 4-8 ounces of cold water 1-2 hours before exercise.
** Teenagers 13-16: 8-16 ounces before activity.
** During exercise: 5-10 ounces every 20 minutes (lower end of scale if younger; upper end if older)
** After exercise: 16-24 ounces of fluid for every pound lost during activity

© 2005 HMS Publishing, Inc.
Jim Brown will be contributing new content to this site on a monthly basis. If you have a question for Dr. Brown please feel free to email him at
sportsmed@mindspring.com.

 

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