People lose fluids by sweat and urine at different rates due to their body mass, their metabolic rate, their core temperature and the air temperature and humidity. When water is lost through perspiration and urination, the blood volume becomes concentrated and the molecules and particles in the blood attract water out of the salivary glands and the mouth becomes dry, (Hamilton, 1991). This may be perceived as a wonderful signal to stimulate thirst. However, since the blood becomes depleted of water before the mouth becomes dry, the sensation for thirst is actually a delayed metabolic response. Unfortunately, this is why the sensation for thirst lags behind dehydration. The bodys demand for water is high since approximately 60% of the entire human body is water, and approximately 70% of our muscles are water. Because the body cannot readily store nor effectively conserve water, it is essential to replace lost fluids.
Tap water is a great for meeting your basic hydration needs. Many bottled waters are marketed with the claim of having improved flavor and being purified. However, when it comes to hydration, there is no research evidence that shows a difference between tap and bottled water. Most people do not realize bottled waters are not regulated by the Food and Drug Administration (FDA). Many bottled waters are simply filtered tap water manufactured to taste better and sparkle more. Brands labeled, Natural Spring Water, legally have to be from a natural spring unless the words are part of the companys brand name. Waters that are labeled as distilled are filtered through a reverse-osmosis system, and are the most purified sources of bottled water (Colgan, 1993).
Fitness waters also known as designer waters are great tasting with very few added calories and just a sprinkle of vitamins and minerals. When is a designer water useful? If you are burnt out on plain water and want some added flavor without a ton of calories, reach for a fitness water. Several popular fitness waters are: Propel, Reebok, Life O2, and ChampionLyte (Applegate, 2002). The basic recommendation is to use plain water for any exercise activity lasting up to 60 minutes. An exercise activity exceeding 60 minutes should include water and a carbohydrate source. Research has shown that after 60-90 minutes of continuous aerobic activity, most storage areas for glucose are depleted. Glucose, a by-product of carbohydrate metabolism is stored in the circulating blood stream, the muscle, and the liver in the form of glycogen.
Sports drinks should be the beverage of choice for activities exceeding one hour in order to provide both a carbohydrate source for energy and adequate hydration. When choosing a sports drink, the carbohydrate content should be 8% or less to facilitate fast absorption. A sports drink with more than 8% carbohydrates, will take longer to digest and may cause stomach cramps (Coleman, 1995). Most sports drinks provide carbohydrates in the form of glucose, sucrose, fructose or maltodextrins, and a dash of electrolytes such as sodium and potassium. For adequate refueling, consume 5-12 ounces every 15-20 minutes during workouts lasting more than 60 minutes. Several popular sports drinks are: Gatorade, Powerade, All Sport and G-Push (G2). Diluted juices at ½ strength are another great source of water and carbohydrate. Any carbohydrate source will fuel the muscles; for example, licorice, marshmallows, gummy bears, etc.). However, the focus for selecting a carbohydrate source should be on nutrient density and optimal health.
In order to be adequately hydrated you need to know your sweat rate. To determine your sweat rate, weigh yourself naked before and then immediately following an event to determine the amount of fluid lost. For every pound of weight lost, you must replenish with 2 cups (16 ounces) of water. Water loss is due to the intensity and duration of the physical activity and the climate. When you exercise and deplete the muscles of stored carbohydrate (glucose), your body also releases water. Water is lost when carbohydrates are burned for fuel because for each ounce of carbohydrate you store as glycogen, your body stores three ounces of water. Many experts agree on consuming one ounce of water for every two pounds of body weight for basic hydration (Gastelu, 1997). In general, clear, frequent urination, every 1½ - 2 hours, indicates adequate hydration.
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Coleman, M.D., Ph.D., and Glenn Tisman, M.D. Total Nutrition from the Mount Sinai School of Medicine. St.Martins Griffin, New York: 1995.
Gastelu, Daniel, Dr. Fred Hattfield, Dynamic Nutrition for Maximum Performance, Garden City Park, NJ: Avery Publishing Group, 1997.
Hamilton, Eva May
Nunnelley, B.S., Eleanor Noss Whitney, Ph.D., and Frances Sienkiewicz,
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