There are different ways to eat for an endurance event such as the Ironman, but the main takeaway is there is no one size fits all approach. Make sure you do trial and error and see what works best for your body. With that said, I want to go over some general rules that will help you fuel for endurance events.
The first topic is carbohydrate loading. The most important pre-event for carb loading is breakfast and lunch the day before, not the dinner. Add extra carbohydrates to both of those meals to ensure that you will have adequate glycogen in your tank on race day. Your body is limited with the amount of glycogen it can store, so over eating to the point of being uncomfortable will not help. Also, excess carbs/food will be turned into fat if you are not careful.
I competed in the Ironman Wisconsin three years ago. The morning of the race, I ate a huge bowl of oatmeal with fruit and nuts two hours before the race. I stuck with what worked for me in the past and felt good before the swim.
During competition, consuming some protein will help prevent muscle breakdown and damage. You want to consume a solution of 1.2g of protein per kilogram of body weight during normal training days.
Learn to consume solid food during racing. This will allow you to process fluid better because the majority of your fluid can now be water. Hydration can make or break your performance. So find out what food works best and what you can easily digest. Try to take in solids when your heart rate is low and stick to fluid calories when your heart rate is high.
Remember eating before exercise and practice is different than eating during exercise and competition. You need to train your stomach to assimilate calories and the more the better. That does not mean eating on a trainer in controlled conditions of output. Your best bet is gels and liquids because they are easy to carry and digest. However, if the race is long enough, a diet of nothing but maltodextrin will make your stomach hurt and cause you to stop covering your caloric needs. You really need to experiment and see what works best on your stomach. For short, hard races choose only liquid and gel. I say this not just for convenient consumption but for rapid assimilation at higher heart rates. For longer races, a mix of solid and liquid will be more tolerable and, depending on the solid food choice, may help calm the stomach. Look at it like this: eat for your heart rate. When it’s high, use liquid and simple. When it’s low/medium you can use solid, more complex food but small doses, less than 100 calories at a time.
My Ironman race day nutrition went well and it took a lot of practice to figure out what worked. I took in the majority of my calories on the bike and used honey stinger products because t hey did not have many ingredients and were natural.
You need to learn to eat based on the training goal. If you are trying to help the aerobic channel, than you want to do it on as little food as possible so you burn fat. Not on a depleted state but usually in the afternoon well after your breakfast. When you are training with a heart rate less than 85% you should only sip a carbohydrate solution. Again when the intensity is low, teach your body to fuel output with fat so you can spare glycogen.
When the training session is metabolic and high intensity, fill yourself up with glycogen before your session. You will also want to take in carbs during and after the entire session to recover quicker. These should be truly hard sessions and you will not be able to do multiple days in a row if you are doing them correctly.
To summarize:
• Over-eating carbohydrates in the one-two days before an event has been shown to positively affect performance.
• Supplement protein intake during the event with a slow acting protein or BCAAs to prevent muscle soreness, damage and to increase threshold performance.
• Water is still the best choice for hydration. It is better for keeping core temperature down which minimizes dehydration and also absorbs better than carbohydrate drinks.
• As much as possible eat your calories instead of drinking them. Although you will need to ensure you are working at moderate intensity so as to avoid gastrointestinal upset.
Everyone has different nutrition needs and remember everyone responds differently. Don’t test something new on race day and make sure you have plenty of trial and error leading up to your most important race.
