Before a discussion can begin on what is best to put in your body, first understand the concept of hydration and its function. Approximately 40 to 60% of a person’s body weight is comprised of water, 65 to 75% of the weight of muscle and up to 25% of the weight of fat. Water is essential to life. It assists in the lubrication of joints, serves as the body’s transport system, aids in the elimination of waste products, and most importantly – in regards to sports and fitness – helps to stabilize the body’s core temperature. Lack of proper hydration can lead to dehydration, when a person can experience an increase in their heart rate, and a decline in cardiac output (the amount of blood ejected from the heart and made available to the rest of the body) by up to 1 liter per hour. The body can become hyperthermic (its core temperature can rise). Studies have shown that even a loss of two percent of one’s body weight due to sweating can lead to muscle cramps, dizziness and fatigue.

While most experts agree on the importance of maintaining a hydrated body, the amount needed tends to be an individual issue, and depends on your health, how active you are, where you live and if a woman is pregnant or breast feeding. The Institute of Medicine recommends that men consume approximately three liters of beverages per day (about 13 cups) and women consume about 2.2 liters of beverages per day (about nine cups). Many still follow the “8 x 8 rule”; drink eight, eight-ounce glasses of water per day. This supplies 1.9 liters of water per day. While this approach is not supported by scientific evidence, it does help to keep a person’s hydration level within the necessary range. Heidi Skolnik, MS, CDN and team nutritionist for the New York Giants also points out that the fluid ingested to maintain hydration levels does not necessarily need to come from water; other beverages – milk, tea, fruit juices – are helpful. She also said that food is a source of fluid replacement. On average, food provides about 20% of the fluid intake, while beverages make up the remaining 80%.

When a person exercises, however, it’s a whole new ball game. According to the book Exercise Physiology, Energy, Nutrition and Human Performance, “the severe loss of fluid that can occur from a prolonged exercise bout places a significant strain on circulatory function that ultimately impairs the capacity for both exercise and thermoregulation.” The primary aim of fluid replacement is to help with the cooling process of the body. And if a person intends to exercise at a moderate to high-intensity level for 60 minutes or more, sports drinks are recommended. The American College of Sports Medicine (ACSM) suggests that the consumption of beverages containing electrolytes and carbohydrates can help sustain both fluid-electrolyte balance and exercise performance. But beware, since not all sports drinks are alike. Look for those that contain six-to-eight-percent carbohydrates. It is thought that anymore than eight percent carbohydrates can cause a fair amount of gastrointestinal discomfort. Another ingredient to look for in sports drinks, according to Skolnik, is sodium. “This is the electrolyte crucial for fluid balance,” she said.

There are no specific recommendations as to the amount of fluid or electrolyte/carbohydrate replacement because of the variability of sweat rates and fluid loss of individuals. It’s basically a trial and error process. A person needs to hydrate before an exercise session, maintain fluid intake during the session – sports drinks for exercise bouts longer than one hour – and continue to hydrate after finishing. Visit www.iom.edu or www.acsm.org for hydration needs specific to certain situations (environmental, medical) as well as amounts to be ingested before, during and after exercise periods. Also, be sure not to take in too much fluid during exercise. This can lead to a condition known as hyponatremia, or water intoxication. Although rare, this can also decrease the sodium levels in the blood. A good rule of thumb for fluid replacement is to try to match the sweat loss; don’t gain weight during a workout or lose too much.