Hydration and Electrolytes: When do they matter?

To listen to advertisements for pre-workout products, sports drinks, electrolyte replacers, and recovery beverages, you’d think every person who exercises needs to worry about maintaining optimal fluid and electrolyte balance for every workout. While there is no harm in vigilantly replacing sweat losses, please rest assured: most fitness exercisers and athletes who train for less than 60 to 90 minutes a day are unlikely to become dehydrated or depleted of electrolytes. That’s most of us!
Indeed, certain athletes should pay close attention to maintaining a proper fluid and electrolyte balance, including long-distance cyclists, marathoners, triathletes, and other endurance athletes who train in the heat for extended periods of time. So should soccer players during a hot-weather tournament, competitive tennis players baking on sunny tennis courts, football players training in full uniform during hot weather, and athletes who simply sweat a lot. (Some athletes sweat more than others; sweat rates vary widely!)
Dehydration can happen during one bout of intensive exercise; other times, it sneaks in over several days of hot weather. The longer your exposure to heat, the greater your risk of becoming dehydrated. That’s why soldiers, construction workers, and gardeners who are exposed day after day to hot weather should have a fluid plan that contributes to a need to urinate at least every four hours. The goal is to lose no more than 2% of your body weight during a workout. That’s three pounds of sweat for a 150-pound athlete (as calculated from pre- and post-exercise weigh-ins). Minimizing dehydration during exercise contributes to a far easier recovery. Post-workout, you’ll feel better and have more energy during the rest of your day. No need to feel zapped!

The following hydration facts and fallacies can help you better survive training and competing in today’s hotter climate.

• Being well-hydrated makes exercise feel easier. Your body functions best physically and mentally when it is in fluid and electrolyte balance—not under-hydrated and certainly not seriously dehydrated.
• When you exercise dehydrated, your muscles, heart, lungs, and brain function less efficiently. These negative effects get amplified by heat and your performance will decline. In a study with cyclists who biked for two hours in the heat, those who drank too little and lost 2% of their body weight reported higher heart rate, perceived effort, and glycogen use compared to the 1% dehydrated cyclists.
• Interestingly, many top marathoners lose 5% to 6% of their body weight (a gallon of sweat!) during a marathon. Would they perform even better if they could drink more? Seems likely.
• As humans, we cannot adapt to dehydration, but we can adjust to the feeling of being dehydrated. That is, if from time to time you train underhydrated, you will become familiar with how it feels. The far wiser path is to learn to prevent dehydration by matching sweat losses with fluid intake. Practice doing this during training sessions!
• Your desire to drink is controlled by feedback loops that make you feel thirsty (or not). The feedback is based on losses of water and sodium from the kidneys. Tanking up two hours before exercise allows time for the kidneys to process and eliminate the excess before you start to exercise. During exercise, kidneys conserve water and produce less urine; hence you’ll experience less of an urge to urinate.
• The right balance of body fluids inside and around cells gets regulated by electrolytes such as sodium and potassium. The concentration of sodium in your blood actually increases during exercise because you lose proportionately more water than sodium—unless you overhydrate by drinking too much plain water during extended exercise. (Bad idea!) The more you train in the heat, the less sodium you lose because your body learns to conserve sodium (and other electrolytes).
• An effective way to help maintain fluid and electrolyte balance is to consume about 500 milligrams of sodium 90 minutes before you start to exercise in the heat. That’s as simple as adding extra salt to pre-exercise oatmeal, eggs, or potato before you exercise in the heat. Doing so will help retain fluid, delay dehydration, and enhance endurance.
•  In general, commercial electrolyte replacers are more about convenience than necessity. Real foods like olives, pickles, and crackers with cheese after a sweaty workout can “work” as well as a commercial product. You just need to plan ahead and buy the salty foods so they are readily available (and that just might not happen…).
• Athletes who sweat heavily might lose about 500 to 700 milligrams of sodium in an hour of vigorous exercise. While a sports drink is handy during exercise, real foods offer more sodium afterwards. (Eight ounces of Gatorade can offer less sodium than a slice of bread.) Some options for replacing sodium losses include:

• In a study with subjects who drank either whole milk, skim milk, orange juice, or a commercial replacement solution, the beverages that retained fluids best were whole and skim milk. That’s because milk has a strong electrolyte content and rehydrates better than a low-electrolyte beverage (i.e. plain water). Carbs, along with electrolytes, further stimulate rapid fluid absorption. For post-exercise recovery, chocolate milk is an excellent carb-electrolyte choice. Plus, it also offers protein to help repair and build muscle. And most importantly, it’s yummy. Let’s drink to that!

Boston-area sports nutritionist Nancy Clark MS RD CSSD counsels both fitness exercisers and competitive athletes. Her best-selling Sports Nutrition Guidebook is a popular resource for answering your food questions. Visit NancyClarkRD.com for more information.