In just a couple of minutes you can determine your nutritional requirements for your 70.3. I use the My Fitness Pal app to record my daily nutritional input and minutes of exercise. I use a 60-20-20 percent for fat, carbohydrates, and protein, respectively, with the sweet spot being 130 grams of carbs.
Here is the break down of how many calories I will need for the entire event with a goal of 6 hours 20 to 30 minutes..
swim: 42 minutes = 605 calories
bike: 195 minutes = 3370 calories
run: 135 minutes = 1750
total calories = 5725
With traditional carbo loading on the two days prior to the race and a pre-race meal, I should begin the race with approximately 2500 calories.
If I subtract the calories burned from the swim from the 2500 I begin the race with, I get a balance of 1895
calories.
Now I divide 3370 (calories for ride) by 56 and I now know that I will burn approximately 60 calories per mile on the bike.
The next step is to determine at which mile on the bike I should bonk or hit the wall: 1895 /60 = mile 30.
This means that I have approximately 26 more miles on the bike which is followed by a 13.1 mile run after burning the original 2500.