BY NANCY CLARK
PHOTO BY PETER SPURRIER
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Steaming hot summers bring up nutrition questions for athletes who are training and competing in the heat:
* How can I tell if I’ve had enough to drink?
* Should I be consuming extra electrolytes?
* Is it possible to drink too much?
With summers getting hotter and longer, here are some practical hot-weather sports nutrition tips.
To start, let’s look at the physiology of keeping the body cool. Normal body temperature is 98.6°F. When you exercise, your body temperature increases. At 104°, you are in the danger zone. If you were to really overheat and get to 107.6°, your cells would get damaged–similar to how raw egg white coagulates as it starts to cook. You don’t want that to happen!
To dissipate the heat generated by working muscles, blood flow to the skin increases, and your sweat glands get activated. As sweat evaporates from the skin, it provides a cooling effect.
Humid heat (New England) is physiologically more stressful than dry heat (Arizona). Hence, athletes who will be traveling to a sporting event want to acclimatize to the environment in which they’ll be competing.
With repeated training in the heat for more than an hour a day, the body acclimatizes over the course of seven to 14 days. You’ll notice greater exercise capacity. In one study, endurance increased from 48 to 80 minutes.
The more you train in the heat, the more you sweat. While this helps keep you cooler, the additional fluid loss can easily lead to progressive dehydration if you do not fully replace sweat losses on a daily basis.
Sweat losses of two to three pounds per hour are common among athletes who exercise vigorously in the heat; some lose more than that. You don’t need to replace every drop of sweat, but you do want to minimize losses, so you end up losing less than two percent of your body weight (three pounds for a 150-pound athlete).
“Drinking to thirst” generally works for day-to-day living and fitness exercisers, but not always for athletes. Studies suggest drinking to thirst often results in body-water deficits of two percent to three percent among athletes who sweat heavily in the heat. That level of dehydration impairs athletic performance. Hence, Ironman triathletes, marathoners and other endurance athletes should have a drinking plan that balances losses with intake.
To learn how much sweat you lose during exercise, weigh yourself nude before and after a hard workout, accounting for any fluid consumed during the session. If you have lost, let’s say, two pounds per hour (32 ounces, 1 quart), target drinking six to eight ounces every 15 minutes the next time you exercise at that intensity and under those weather conditions. Practice drinking that volume of fluid to train your gut to handle it comfortably.
Monitor progressive under-hydration by weighing yourself daily first thing in the morning. A downward weight trend can be a warning sign of inadequate fluid replacement, particularly if your morning urine is dark and concentrated. (Yes, it could also reflect fat loss.)
You can tell if you have adequately rehydrated by monitoring the color and volume of your urine, as well as how often you need to urinate. For example, if you sweat heavily during your workout and then don’t pee for five hours afterwards, you are under-hydrated. Urine that is dark and concentrated is another warning sign.
On a daily basis, your goal is to void a significant volume of urine that looks like lemonade, not beer, every two to four hours. Google “urine color chart” for a visual resource.
When you sweat, you lose not only water but also electrically charged minerals (electrolytes), specifically sodium, calcium, magnesium and potassium. Sodium (a part of salt) is the main electrolyte of concern.
Because you sweat proportionately more water than sodium, the concentration of sodium in your blood increases during exercise. In standard (i.e., not extreme) exercise situations, replacement with electrolyte supplements is unnecessary; food eaten at meals/snacks offers ample electrolytes.
The primary purpose of sodium in sports drinks is to enhance fluid absorption and retention, as well as foster the absorption of carbohydrates. The amount is inadequate to replace sodium lost in sweat. For example, a slice of bread offers about 125 to 200 milligrams of sodium; eight ounces of Gatorade offers only 110 milligrams. Gatorade Endurance formula: 200 milligrams.
If you’ll be exercising for hours on end in the heat (i.e., all-day bike ride, ultra-run, tennis tournament, etc.), you can lose a significant amount of sodium. Assuming you’ll be consuming food during the extended exercise session, you can replenish lost sodium with peanut butter and jelly sandwiches (500 milligrams of sodium), thin pretzels (490 milligrams per ounce), and cheese sticks (200 milligrams per stick).
Caution: Do not overconsume plain water and/or sports drinks during extended exercise unless you are taking in other sources of sodium. Excess water dilutes the reduced amount of sodium in the blood and can lead to hyponatremia (low blood sodium), a life-threatening condition that can result in death. This can happen, for example, with slow (four-hour) marathoners who diligently drink at every water station, regardless of thirst.
After exercise, if you need sodium, you will crave salt and should honor those cravings with crackers and cheese, pickles, pizza, potato chips, V8 Juice–or more simply, sprinkle salt on your recovery meal.
Most healthy, sweaty athletes can ignore the public- health directive to “limit your salt intake.” Replacing sodium losses is important to rebalance your body.
When you know you’ll be sweating for more than an hour or two in the heat, plan to boost your pre-exercise salt intake. By consuming 300 to 500 milligrams of sodium before you exercise, the sodium will already be in your body, working to retain water and retard dehydration. During extended exercise, aim for 500 to 700 milligrams of sodium per hour (and more if you experience muscle cramps).
Chocolate milk is preferable to a sports drink to enhance rehydration. It offers more sodium (150 milligrams versus 110 milligrams per eight ounces) as well as more carbohydrate (to replenish glycogen stores) and protein (to repair muscles). Drink wisely!
Sports nutritionist Nancy Clark, M.S., R.D., counsels sports-active people in the Boston area (617-795-1875). Her Sports Nutrition Guidebook offers additional hydration information. For more, visit www.NancyClarkRD.com.