Fueling your body during a run is, as I’m sure you can imagine, a really big deal. Many runners use gu during events of a half marathon, and close to 90% use some form of sports energy during the marathon.
For an ultra, mishandling your food can destroy your event. Trial and error is the only way to figure out what is going to work for you. The one factor that is the same regardless of how you fuel is using small amounts frequently rather than eating a larger amount. A quarter of a peanut butter and jelly sandwich is going to be easier than the whole sandwich. The other rule, which cuts across all aspects of running, is train with it before you race with it. After that, there are four approaches to maintaining your energy during an ultra.
First, is to use sports energy options, such as gu, stinger, or hammer gel, throughout the run. There are a few ultrarunners who do this. Sports energy delivers a fast supply of sugar, which is what your muscles are burning. Personally, I’ve never been able to do it this way and none of my runners have been able to do this. The gels and such become torture to get down. Even if you like them, by mile 75, you won’t. Your body needs a little more than just sugar when you are moving for more than 24 hours. That’s where the other approaches come in.
Second, is to use a mix of sports energy and regular food. A lot of the runners I work with, even marathoners, choose this option because it gives them quick energy and a more sustained slow burn energy. To implement this strategy, find some foods you think are easy to digest such as fruits, potato chips, candy, cookies. These still give you the carbs you need, but they take a bit longer to get to the muscles. You can throw in small amounts of protein as well, which slows the breakdown of the muscles in the later part of the run. Be cautious and chose easy to digest proteins such as nut butters and protein bars or drinks.
Third, is all regular food. I use solid regular food throughout my runs. You want a mix, again, of slower and faster digesting items. With solid foods, you need to keep in mind it takes longer to digest so you will need to eat before you need the energy, rather than when you are starving. The other problem with waiting until you are hungry to eat, is you over eat. Over eating can cause stomach irritation.
Fourth, is low carbohydrate. Low carb is a life style not merely used during an event. It requires the runner to stay below a certain amount of grams of carbs everyday, which allows them to burn fat rather than the glycogen in their muscles. Fat is an excellent source of energy. However, being low carb also requires the consumption of a lot of fats as well. Consuming a lot of fats is not necessarily bad. The research is a mixed. The type of fats a person consumes does make a difference. Anyway, low carb runners have to bring their own food (same as vegan runners). In theory, they don’t have to consume many calories because they are burning the fat. That was not my experience. I was low carb for 18 months and found I was not able to consume enough fats to maintain the energy I needed to run ultra-distances. Some low carb runners use a product called Vespa which enhances the body’s ability to burn fat. Others supplement with high doses of sugar at strenuous times (big climbs) during the event to give them the extra boost. The sugar hits their system fast and furious because it doesn’t get it very often.
Regardless of the approach you use, practice during training runs is the key. You have to train your body to digest at the same time it sends energy to muscles. Use trial and error to find what works for you. Keep in mind that it is best to try one thing at a time and to give your body a couple of weeks to decide if it is alright with it. When you introduce a new thing, it may cause some issues at first, but those may go away with continued use.