It seems there's virtually no end to the power and stamina of Olympic athletes, which is due in part to the detailed guidance they get from experts about the right amount and type of food they need.
So what do Olympic athletes eat? A lot.
On average, they need to consume between 33 600kj and 42 000kj a day, compared to just 8400kj to 10 080kj a day for the average moderately active man, according to the Academy of Nutrition and Dietetics.
The science of fuelling athletes for elite sports goes way beyond kilo joule intake to include percentages of carbohydrates versus proteins, quantities of fluid and the timing of meals and snacks.
"There is a huge range of different needs, depending on the event and how much speed, endurance and strength the athlete needs," said Dr Christine Gerbstadt, a registered dietician and anaesthesiologist in Gaithersburg, Md.
The advice athletes get has changed a lot in the past 20 years, Gerbstadt said. "You used to see an NFL football team sit down to a huge steak dinner before a game," she said. "No more."
Instead, the new approach is designed to feed athletes not just a combination of foods they need prior to an event, but to ensure that they ingest the right nutrients to help repair their muscles for the next competition, Gerbstadt said.
Nutritional needs for athletes
There are three phases to consider when planning the nutritional needs of athletes, Gerbstadt explained. An hour or two before an event, the Olympians should have an easily digestible light meal - ideally oatmeal and a banana with milk or yoghurt. An hour or so before the competition, they also need 16 ounces of water.
Hydration is a big issue, said Amy Jamieson-Petonic, a registered dietician and director of wellness coaching for the Cleveland Clinic.
"Athletes can lose 2% to 3% of their body weight from dehydration, which can negatively impact their aerobic performance," she said.
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 3360kj 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 fibres."
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 athletes is also highly individualised, going beyond their sport to their particular preferences. "Everybody's got something a little different in their sports bottle," Gerbstadt said.
Lesson for everyone who exercise
Although most people will never experience the athletic demands Olympians face, there are some important lessons from the nutrition experts for everyone who exercises:
If you wonder whether you get enough hydration when you exercise, try weighing yourself first thing in the morning and then again right after your workout. The decrease in weight will represent the amount of fluid you lost, Jamieson-Petonic said. You'll need to replace every pound you lost with 24 ounces of fluid, she added.
Concerned you might be dehydrated? It will probably be evident through your performance. "You feel like you just can't go on, your body can't do what it's used to doing," Jamieson-Petonic said. "You can walk but you can't run."
Don't roll out of bed and go straight to a 5K run without some breakfast, Gerbstadt said. "Be sure to get some carbohydrates, lean protein and fluid on board before you go."
(Health Day, July 2012)
2012 Olympic Schedule