Fueling During Exercise


Now that I’m actually going to run a marathon, I think it’s important to learn about fueling while running. The other day I was trying to research online about a few of the guidelines for fueling during races, and it was kind of difficult. There is no perfect formula for fueling during exercise – only estimates.

This is because we are all different and so are our bodies. Some people might have no problem eating a slice of pizza a few minutes before their run, while others might have serious stomach problems. Some people might need to fuel every 25 minutes of a long run while others might not have to for 45 minutes. The bottom line is that what works for one person might not work for another. With that being said, here are a few general guidelines I found for fueling during exercise.

A Few General Guidelines

  • Fuel during exercise that lasts longer than 1 hour. There is no proven benefit for people to fuel for exercise that is shorter than this.
  • Ingest 30-60g carbohydrates for every hour of exercise.
  • Ingest sodium for exercise lasting longer than 2 hours.

Why to Fuel During Exercise?

Our bodies are pretty awesome at using stored energy and converting it into usable energy. However, our bodies can only do so much. Therefore, we need to do everything possible to make it easier on our bodies and therefore improve our performance.

When we ingest fuel during exercise, it’s kind of like giving our body a break. Our glycogen stores are easily converted to usable energy, but fat can be harder to convert. The fuel we ingest is easily accessible and it also helps to spare our glycogen stores for when we really need them (the end of the race).

Fueling during exercise also helps to maintain our blood glucose levels or “blood sugar”. That way we don’t “bonk” or get that awful dizzy/weak feeling. Our bodies can stay strong and keep our motor skills sharp, which is crucial in a race.

My Experience with Fueling

I think the farthest I’ve run before was about 15 miles (roughly 2 hours of running). For me, I don’t really fuel for runs that are shorter than 10 miles and for my 15-mile run I only fueled once. Therefore, I don’t have much experience with it.

I’ve run a couple half marathons where I’ve ate along the way, but I’ve also run some that I haven’t fueled for (not including water) and I haven’t noticed much of a difference. My personal experience is that I don’t necessarily need to eat during half marathons. However, I know that for a full marathon almost everyone needs to fuel so that they don’t hit the wall. Here’s the link to my previous post about the importance of carbohydrates in avoiding the wall.

I’ve tried out eating GU’s, crackers, power bars, and blocks. I now prefer GU’s as they are really easy to eat while exercising. Chewing and breathing hard just don’t go well together in my experience. It normally ends with me semi-choking.

Last weekend I went to a local running store that I had a gift card to and spent it all on GU’s.



I got a mixture of lemon-sublime, salted caramel, vanilla bean, and peanut butter. I wish the store had the chocolate-mint type as I remember REALLY liking that flavor. I didn’t want to get ones with that much caffeine in them just because there isn’t much caffeine in my diet. Since my body isn’t used to it, I don’t really want to test something new out right now.

I tried some GU’s on my long run and found that they worked well. They were pretty easy to eat and tasted fine. My only complaint is that they were a little messy since there weren’t any trashcans for me to get rid of the wrappers in, so I had to stuff them back in my coat pocket. EW! I’ll be able to have a better idea of how well they work for me once I get closer to race day and my long runs get longer.

How to Find What Works Best for You

Experiment. You’ll never find out what works best until you try it out. You shouldn’t expect that it would be fine to eat and drink during a race if you haven’t practiced it before. Our bodies need time to adapt! If you start experimenting long before your race then you will probably find something that works well and will therefore work well during your race.

Since I’m pretty inexperienced with fueling during exercise, I would love some advice. I’ve taken nutrition classes where I’ve learned about fueling, but nothing is better than real-life experience.

What works best for you? What doesn’t work well? Thoughts?


26 thoughts on “Fueling During Exercise

  1. I agree that the only way to find out what works for you is to test out different things. 🙂 No one products affects each runner the same. Nothing new on race day though! That being said, I love Island Boost and Accel!

      • Island Boost is a gel… but it’s more liquidy than most gels. It’s like an instant rush of energy. I LOVE it. Accel is a gel too. I like it because it’s a 3:1 carb:protein ration and some of their flavors have caffeine too. Because it’s mixed with protein, it’s less harsh on your tummy.

        • Awesome – thanks for letting me know! I think GU is probably the big brand name out there for gels, but there definitely a lot more (possibly better) gels on the market.

  2. Another general guideline is that the more intense an activity is, the earlier you have to eat prior to it. For example, when running the 800m, you probably don’t want to eat anything too solid within the preceding 3 hrs. The corally is true too: low-intensity, long-duration events allow for food consumption almost until the event starts.

    Running is a high sweat rate sport. Sodium needs per hour can be between 2x and 3x a sedentary person’s. As a result, many runners underestimate their sodium needs, especially when it is humid and they are running for a long time.

    I never really like using Gu or any of its competitors, because they are expensive for what they are and don’t actually provide a substantial nutritional benefit over at-home concoctions. My favorite at home concoction was (1) Maple syrup or honey, mixed with (2) water, and topped off with a little (3) salt. Dextrose works too, but it is totally flavorless and the mouth feel it produces is, in a word, unappetizing. I prefered using this approach because it allowed me to adjust consistency and sodium content. As an added bonus, it is substantially less expensive than buying energy gels and it doesn’t create as much waste, if you are using a refillable flask.

    By the way, I enjoy reading your blog. Keep up the good work!

    • Thanks for the info, Sully! I’m glad you’re enjoying my blog. 🙂 That “concoction” sounds pretty good and easy to make. I love maple syrup so I’ll probably try that out.

  3. Great post! Experimenting is definitely the best advice, no matter what people swear by, you never know what’s going to work for you and a race is not the time to try things out. I fuel for long runs only if I’m planning on making a hard effort, if it’s an easy pace long run then I don’t fuel, unless I were to go over 3 hrs I guess.. For a half marathon I would fuel around the half point since I’m making a hard effort, no fuel during a shorter race. Never ran a marathon but I guess I’d fuel at least twice (training for one will allow for experimentation).

  4. I’m not a fan of Gu. It makes my stomach sour and it’s too sweet. I’m testing out Generation UCAN mad thus far love it. My husband is a distance swimmer and has been using it a couple years.

  5. Since I’ve only run 5 miles I have zero experience with fueling, but I love this post because as I train for a half marathon I’ve been thinking about this. Great post! Thanks for the tips!

  6. Mmm, the salted caramel flavor is really good! I definitely need water to get those things down though (one of the many reasons I love running along the Esplanade- water fountains!).
    I also enjoy Swedish Fish 🙂

    • I’m excited to try the salted caramel! I feel like I will either love it or hate it – hopefully love it. mmm, swedish fish sounds good! I might have to experiment with that.

  7. Great post! Experimenting and figuring out what works for you is definitely key. I used to do Gu all the time but am now in a “non-gel” phase (just got sick of them) and am doing the Cliff Bloks…will probably go back to gels someday tho!

  8. I’m a big proponent of the Clif Shot Bloks for long runs. I find them easier to eat than the gels as the gels do get quite messy. On my training runs over an hour I also swap out straight water for a nuun.

  9. Bananas and grape sugar / dextrose works fine for me. I never consume any artificial nutritional supplements, it’s too unclear to me what they contain, how they are manufactured. Take a granola bar or two as well and you are set for two to three hours. A Marathon ist different…but I will only do a marathon based on healthy, organic, sustainable food.

    • I definitely like the idea of eating more natural and organic food when I’m running. I’ve tried eating bananas before my run and it’s worked great, but never on my run. Maybe I’ll try that out. Thanks for stopping by!

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