I recently completed a half marathon, and it seems that my body was able to store enough calories to allow me to stay running at a constant pace through the entire race. Although I felt good through the 13.1 miles, my next target is a full marathon, and I am told that at some point the body will run out of available calories at which point it will become necessary to take on calories for a variety of reasons. The most obvious reason being a degradation in performance. My question has two parts: how many calories and how often should I take nutrition through a full marathon and what natural products can you suggest (e.g. bananas and peanut butter)?
Dear SatSat (Jesse),
Congratulations on your half-marathon, and for your well thought-out question. You will indeed need to take on more calories in order to complete your marathon.
Sports nutrition can be complicated or it can be very simple. I am opting for a fairly simple approach: Determine calories, choose how you will get those calories, how you will carry them, and when you will ingest them. Because everyone is unique when it comes to what works for them, I only have one rule: practice, practice, practice.
To determine a baseline for number of calories, try this formula, developed by Kim Mueller, M.S, R. D. (Note: there are other ways to determine this, but they will all give you a ballpark range which you can fine tune to meet your needs).
1, Determine Running Calorie Expenditure per mile by taking your body weight and multiplying it by 0.63 Example:150 pound runner X 0.63= 94.5 calories per mile.
2. Determine Realistic goal pace for your race per hour, for example at 10 minute miles you would cover 6 miles an hour.
3. Calculate hourly expenditure based on goal pace: In this case 6 miles an hour x 94.5 calories a mile= 567 calories per hour.
Since you ran your half marathon without any need for additional calories, my suggestion is to go the first 60-90 minutes just drinking water. Research shows that you can replace up to 30% of calories per hour- take in much more than that and your body will not be able to absorb it, and you risk G.I. distress.
4. The formula for goal calorie replacement would be 0.3 X the calories per hour, or in the example above: 0.3 X 567= 170 calories per hour.
So, for example, if you were running a 4:22 marathon (10 minute miles), and you just did fluids for the first 90 minutes, that would leave you with approx. 3 hours to fuel for. So at 170 calories an hour, that would leave you with 510 calories to ingest in the final 3 hours.
As far as what kind of natural foods you take in, here are some suggestions:
- 2 Fig bars, approx: 198 calories
- Small box of raisins: 123 calories
- ½ cup of mashed sweet potato: 125 calories
- Medium size sliced apple: 77 calories
- A large banana: 121 calories
This is by no means a complete list, but you can get an idea of how much you would need to carry to get to (in this example) your goal of approximately 500 calories.
If possible, it is preferable to take in calories at frequent intervals, rather than loading up in one gulp. Try to time it with the water stops in your race.
At most races it is illegal to receive outside help, so you need to figure out how to carry your food. A product such as a Spibelt which has a lightweight but expandable pouch is an excellent choice, or perhaps a FuelBelt, if you are going to carry your own water as well.
I love that you used the phrase “at a constant pace” in your question. It indicates consistency, and that is the key to all good racing and refueling. Best of luck in your marathon.