Trainers and coaches regularly check their athletes' specific gravity and osmolality (measures of dehydration), she added.
Some sports are more likely to lead to dehydration than others, Jamieson said. Swimmers typically are at high risk for the condition because they typically can't grab a sip of water in the middle of the event.
If an athlete's event is an hour long or less, they shouldn't drink water during the competition, Gerbstadt said. If it's more than an hour, the amount of water they should drink depends on the temperature, humidity and how much they actually perspire.
Gerbstadt recommends drinking 16 ounces of water, juice or a sports drink anywhere from every 15 minutes to every hour, depending on the individual's needs.
"They shouldn't go overboard on the fluids," she said. "It's actually better to be under-hydrating than taking in too much fluid."
After the event, in the "recovery" phase, the goal is to help the athletes' bodies bounce back quickly. The average Olympian burns about 800 calories an hour, but that can be replaced gradually over four to eight hours, Gerbstadt said.
She advises athletes to eat a quick recovery snack as soon after the competition as they can -- preferably 20 to 30 grams of protein and carbohydrates.
"A fruit smoothie with protein powder would be ideal, or a turkey sandwich is great," she said. "Without the immediate snack, there will be a prolonged recovery time of broken-down muscle fibers."
For most Olympic athletes, one of the hardest aspects of nutrition is finding the time to consume all the calories they need, said Jamieson-Petonic.
"They're training so hard, they have to literally plan to eat and drink multiple times a day," she said. "Because their nutrient needs are so high, they have to schedule meals and snacks very carefully."
The guidance that nutritionists offer Olympic a
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