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The Food and Nutrition Board of the Institute of Medicine* (IOM) recently convened a panel to determine the appropriate dietary intake levels of water, salt and potassium necessary to maintain health and reduce the risk of chronic disease.
The panel discussed:
According to the IOM report, “The vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide.”1 The report states that healthy adults do consume enough water from drinking fluids (about 80%) and eating food (about 20%) to maintain health and proper physiological function on a daily basis—an average of about 3.7 liters (125 oz.) for men and about 2.7 liters (90 oz.) daily for women. However, this statement may not be true for individuals with higher than average fluid and electrolyte needs.
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While the IOM report states that most people drink when they’re thirsty to stay hydrated, research shows that this seemingly simple statement may be misleading for two reasons:
- Daily fluid requirements fluctuate greatly for people in hot climates and for those who are physically active. Dehydration resulting from the failure to adequately replace fluids during exercise can lead to impaired heat dissipation, elevated body core temperature and increased strain on the cardiovascular system.
- Behavior, not thirst, is primarily responsible for determining fluid intake. That’s because people typically drink when they’re eating, passing a water fountain or refrigerator and whenever they find fluids readily available, such as at meetings or parties.
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The American College of Sports Medicine (ACSM) and the National Athletic Trainers’ Association (NATA) caution physically active people against “letting their thirst guide them.”1 After all, research shows that thirst—a physiological response to the stress on our bodies from fluid and sodium loss (via sweat, diarrhea or vomiting)—is NOT a good indicator of hydration status or the body’s fluid levels.
Instead, these groups recommend active adults drink before, during and after exercise and other active occasions (i.e., sports, physical work, recreation, etc.) to:
- Regulate their body temperatures.
- Replace fluids lost through sweat—preferably at a rate close or equal to sweat rate to minimize the potential for heat illness. (To determine adequacy of fluid intake, weigh individuals before and after exercise.)
- Stay properly hydrated without overdrinking.
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The IOM report warns that active people should avoid drinking too much, which in extreme cases may result in hyponatremia. Hyponatremia is a dangerous condition that may arise when athletes drink too much water, diluting the body’s sodium levels. Because exertional hyponatremia is so rare, the IOM panel did not set an upper limit for water consumption.
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The average American consumes between eight to 12 grams of salt daily—too much, according to the standards set by the IOM. In its report, the Institute advises healthy adults should consume an average of no more than 3.8 grams of salt (1.5 grams of sodium and 2.3 grams of chloride) each day—going no higher than 5.8 grams.1 This upper limit is based on the suggestion that eating more sodium leads to high blood pressure.
Yet, while cutting back on overall dietary sodium may be sound advice for the sedentary public, it is not recommended for athletes. They need sodium in the diet because they:
- Can lose large amounts of sodium in sweat.
- Have to replenish sweat sodium losses to ensure proper fluid homeostasis in the body.
Instead of cutting back on salt, the ACSM and the NATA recommend that athletes liberally salt their food and consume sports drinks—especially when exercising in hot conditions.
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Thirst, behavior and occasion all drive fluid consumption. That’s why it’s important to consider the practical application of the IOM’s report on an individual basis, since some of its recommendations may not be appropriate for athletes and active individuals. Team physicians, athletic trainers, sports nutritionists, registered dieticians and other professionals who work with athletes must work to make correct interpretations.
In that spirit, it’s important to consider that optimal hydration is the replacement of fluid and electrolytes based on individual needs. A properly formulated sports drink is an effective hydration beverage that helps to replace fluids and electrolytes (including sodium and potassium) lost in sweat by sustaining the physiological drive to drink and by helping maintain fluid homeostasis.
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