One thousand calories. Roughly a third of many athletes' normal daily allotment. That's how many calories you're likely to burn during the swim of an Ironman-distance event. With a 5,000-calorie bike ride and a 3,500-calorie run yet to come, that's a pretty deep hole you've dug for yourself, and the event has only just begun.
There's really no way to avoid burning a ton of calories during the swim—or to prevent an energy deficit by eating in the water—but your performance for the rest of the day depends on adapting your nutrition strategy to compensate for this deficit. Fortunately, a few tweaks to your pre-race routine and your bike-leg nutrition can help you catch up on lost calories from the swim and set yourself up for a strong run.
Keeping Topped Up
Breakfast is the most important meal of the day, and that old adage is never truer than on race day. You burned most of the carbohydrate stores in your liver overnight, and breakfast is your last big chance to pack more carbohydrate into your body. From then on, it's a constant battle between using energy and replacing it.
The body runs on a seemingly flawed system that lets us burn energy faster than it can be replaced; you can easily burn 800 to 1,000 calories per hour, but you can only replace a portion of that. To maximize performance, it's crucial that you start with as much fuel as possible in your body, and that you consume enough calories during the event to maximize the replenishment capacity of the system.
Plan to get up a few hours before the start of the race so you can eat a large breakfast and give it time to digest. For most people, this means sitting down to your final pre-race meal three to four hours before the start. You obviously don't want to go to the swim start with food sitting in your stomach, so practice your race-day plan in training to know exactly what you'll be eating and how much digestion time you'll need to feel comfortable when you start racing.
Before shorter events, like sprint- and Olympic-distance triathlons, you can often get away with a smaller meal about two hours before the race. And for all race distances, it's a good idea to consume a bottle of carbohydrate-rich sports drink in the last hour before the start.