3. Go Easy on Fat
For long events, such as marathons, your body turns to fat for energy when carbohydrate sources run low.
Most athletes get all the fat they need by following the basic dietary guideline to eat mostly unsaturated fat from foods such as nuts, avocados, olives, vegetable oils, and fatty fish like salmon and tuna.
Avoid fatty foods on the day of an event, since they can upset your stomach.
4. Drink Fluids Early and Often
Intense exercise, especially in hot weather, can quickly leave you dehydrated. Dehydration, in turn, can hurt your performance and, in extreme cases, threaten your life.
"All high-intensity athletes should drink fluids early and often," Dubost says. "And don't wait until you're thirsty. By the time you feel parched, you may be seriously dehydrated."
A pale yellow color means you're getting enough fluid. Bright yellow or dark urine means you're falling short.
Because intense exercise makes you lose fluid quickly, it's a good idea to drink fluids before as well as during an event, Dubost says.
Endurance athletes such as marathon runners or long-distance cyclists should drink 8 to 12 ounces of fluid every 10 or 15 minutes during an event. When possible, drink chilled fluids, which are more easily absorbed than room-temperature water. Chilled fluids also help cool your body down.
5. Replace Lost Electrolytes
Sweating removes both fluids and electrolytes. Electrolytes help transmit nerve signals in your body. To replenish them, reach for sports drinks. If you’re also losing a lot of fluid as you sweat, dilute sports drinks with equal amounts of water to get the best balance of fluid and electrolytes.