Fueling for Ultras: 12-24 hours

March 5, 2021

Dear Chaskis,

How do I fuel for REAL ultras, like races that take 12 hours or more?


Every runner questioning how many gels is too many gels

Lucky for you, Chaski coach and ultra runner Kris Brown has offered up some advice on fueling for events lasting 12 to 24 hours. Here's his take on what to do and what not to do when fueling for ultra running.

Full disclosure: Kris is sponsored by Gu (as well as HOKA, Rabbit, and Squirrel's Nut Butter).

Chaski coach Kris Brown

Let’s just get this out of the way: every runner is different when it comes to fueling, whether it’s in daily life or during a grueling mountainous 100 mile race. Courtney eats candy, Jim eats gels, Magda likes liquids, and all three won Western States. Meanwhile, Mike McKnight just ran a 100-mile solo effort in 18:37 on zero calories. So there’s that.

It’s impossible to say what the best fueling strategy is in general, but part of your journey as an ultrarunner is figuring out what the best fueling strategy is for you. And I don’t think it’s impossible to get a pretty good answer to that question over time. And you’ve got time! Lucky you: a big part of training for ultra running is learning to adapt and deal with adversity, not just hitting the right splits for the right number of miles per week, so if you have a fueling pattern during training, break it. Try something new. If it doesn’t go well, try it again next week just to make sure. Go ahead, I’ll wait.

Now, there are some strategies that are more commonly practiced than others, and I would even go so far as to say that there are some strategies that are more likely to work for more people than others, but that’s about the most absolute I’ll get. The rest of what I say is pretty much just going to be extrapolation based on personal experience, plus some myth busting, since there is a lot of conventional wisdom when it comes to ultra-fueling that is at least tinged with nonsense, if not utterly contaminated with it. So without (much) further ado, here’s an outline of a strategy based on my experience that I would recommend to someone with a relatively traditional approach to in-race fueling. But first, a basic premise.

Premise: Race fueling is all about sugar.

Now that I’ve upset the keto crowd, let me clarify: my approach to in-race fueling is all about using sugar, so that’s what I’m going to talk about. It’s clearly possible to rely on fat consumption while running. The fact is, all of us are going to burn a personally patented blend of fat and carbs while running (the faster you go, the more you’re going to skew toward carbs), and it’s possible to train your body to use fat in much greater proportions, but our capacity to store fat is much greater than our capacity to store sugar -- even very lean athletes have hundreds of miles worth of fat stored on them, while in general we run out of glycogen around 20 miles --  and so if you’re going to be using both at a relatively normal ratio, sugar is the one you need to be worried about replenishing.

Chaski coach Ashley Brasovan

Pre-Race Strategy: Don’t eat.

I’m losing almost everyone, here, but I think this is a much better strategy than people are willing to admit, mostly because they’re afraid to start a race without eating. Try it out. After all, when you start running you’re going to be burning energy already stored in your muscles, not the food you ate for breakfast. And if you start the race feeling hungry? Great! You get to start your in-race fueling earlier! So sleep in, folks -- it’s going to be a long day, and those extra couple hours of rest are going to help you more than breakfast. Definitely drink coffee, though...

Did I mention this is my personal strategy, not a guaranteed manual for success? Let’s get to race time.

In-Race Fueling Myth #1: You Should Eat When You’re Hungry

Yes, you should eat when you’re hungry, but you should also eat a bunch of other times, too. Unlike thirst, which is a pretty reliable indicator of hydration, your hunger is not going to keep up with your need for calories. At best, relying on your hunger response is going to lead you to ingest calories too late.

One of the most interesting parts of getting into ultrarunning for me was learning the variety of non-hunger cues that my body could give me that I needed to eat. Sometimes my energy level would dip and I would get grumpy and unmotivated. I wouldn’t feel hungry, so I wouldn’t eat, and I would feel that way until, for whatever reason, I decided to have a gel, and my mood would immediately turn around! I would start to feel positive and motivated, and I could create some momentum that would help me rally and save the last part of a run or race. It’s often confusing, but I find this part of ultrarunning to be a valuable opportunity to learn about my body.

In Race Fueling Myth #2: During long ultras you have to eat real food

This is a tough one. It is conventional wisdom that ultrarunners ought to eat whatever it is they’re craving, and lots of it, which is why aid stations in ultras tend to be elaborate. There’s a prevailing sense in the running community that, considering the intensity of the event, and the likelihood of digestive problems, runners should pretty much eat like maniacs for the duration of the race, gorging on a wide variety of foods to whatever extent possible for as long as they’re able. From a performance standpoint, I think this is a bad strategy.

I’ll admit that sometimes, when things go poorly, eating comfort food (whatever that means to you) is a good strategy to avoid a death march or a DNF, and I’ll get into that later, but in general, I think that the “real” food you’ll find at aid stations -- like quesadillas and PBJs -- will take too long to digest, leaving you feeling low-energy with a gut full of food. Again, I think they’re fine if you’re planning to hike and just want to eat appealing food, but as long as you can stomach gels and sports drinks, they’re going to provide you with more energy, faster, without sitting in your stomach.

It can be hard to eat a ton of gels, but it is also a skill you can acquire with practice. The more I’ve raced, the longer I’ve been able to go without my stomach revolting, forcing me to switch to real food, and the effect on my energy level and the speed I can sustain is undeniable.

So What’s My Strategy?

During a long ultra I aim to consume about 400+ calories per hour in the form of a gel every 30 minutes plus a 200 calorie bottle of sports drink every hour. That’s the strategy I’ll use for the majority of the race. In the first hour or two I’ll allow myself to play it by ear, but once the first gel goes down the proverbial timer starts for the second one. Some people use a literal timer, and I probably should, because it’s easy to lose track of when I took my last gel, especially if your pattern gets disrupted by an aid station.

During the race I’ll also sometimes supplement with fruit or soda at aid stations, but I’ll avoid anything with complex carbs or too much fiber. I learned this strategy the hard way after throwing up a bunch of watermelon pulp at mile 94.

Even while taking in that many calories, I’ll always be alert for signs that I may be getting behind on nutrition because after a tough section or late in the race, I’m still likely to hit a patch of low energy. In those cases I’ll eat another gel between two that I have planned without modifying the schedule otherwise, effectively injecting another 100 calories into that hour. I’ve even switched to a gel every 20 minutes, upping my hourly consumption to 500 calories plus aid station food. If it’s late in the race and your stomach is cooperating, more is better. After all, you’re probably never going to eat as fast as you’re burning.

So if there’s one thing I can emphasize, it’s that running relatively fast for these huge chunks of time takes a lot of fuel. I talk to tons of athletes who have the impression that a gel every 30 minutes and a zero-calorie beverage is enough to get through a 100 mile race. For some it may be, but they could probably sustain a faster pace if they ate a lot more.

But that’s too many gels!

You’re right. It’s a lot of gels and sports drink, and it’s really likely that you won’t be able to manage this protocol for the entire race, so it’s important to have a couple of “oh shit” plans.

“Oh Shit” Plan #1: Gels aren’t sitting right

If this happens, switch the emphasis to sports drink, trying not to reduce the number of calories consumed. Supplement with fruit at aid stations, or whatever else you can stomach, aiming for simple carbohydrates if possible.

“Oh Shit” Plan #2: I’m in an irredeemable bonk, I can’t eat gels, I’m dizzy and puking, and this has been going on for hours

It is very often possible to come back from a situation like this. You likely won’t be able to run well for the rest of the race, but you might actually feel pretty good again, as hard as that is to believe right now. I recommend abandoning your fueling strategy and gorging on hearty food at the next aid station. Once you’ve gotten down several hundred calories, start walking. Since that food is composed of more complex nutrients and since there’s a lot of it, it is going to take a while for it to make you feel better, but if you spend some time walking, you may find that in 30-60 minutes your energy starts to come back. Return to the gel protocol if you want, or just jog it in slowly and keep eating cookies and soup at the aid stations.

Chaski coach Pete Kostelnick celebrating with post-race champagne

Advanced Black Magic Stuff: Not all sugar is created equal

If I’ve convinced you to try running your next race using only simple carbohydrates, unfortunately the work doesn’t stop there. Even within the category of what we can colloquially refer to as “simple sugars,” like whatever is in your preferred gels, chews, or drink mixes, there is plenty of experimentation to be done to figure out how each type of sugar affect you personally, and in my opinion there’s a little bit of magic in this part.

You can look into the glycemic index (GI - a score given to foods related to how quickly they affect your blood glucose level) and you’ll find some variation among different sugars, but I don’t think this totally explains it.

Have you ever heard of the wine concept of terroir? The idea is that two grapes from cloned vines given the exact same treatment will still produce different flavors in wine, probably because of small differences in soil composition and climate. Now terroir has obviously nothing to do with what we’re talking about except that it helps me illustrate the point that “there’s some other shit going on here, and we don’t exactly know what it is, but it’s definitely real.”

I find myself using weirdly druggy terminology like how different sugars have a different “come up” and “come down,” and how they “hit.” I don’t know why some are better than others, but I think it’s real, and you should try a bunch of different products to see how they affect you. Pro tip: watermelon hits really well, but if you overdo it you’re going to end up with a belly full of pulp, so try making watermelon juice for crew checkpoints!

Post-Race Recovery: Mental and physical:

In his last post about fueling for the 50k-100k distances, Tyler wrote about letting yourself eat whatever you want for a little while after a huge effort. After all, you put a lot into the race, and so a little cathartic gorging seems appropriate. I’m totally on board with this, but I would add one caveat.

In addition to eating a lot of whatever you want, I think you should pre-prepare a bunch of really healthy, recovery-oriented foods. Make a bunch of smoothies with insane amount of turmeric to ease inflammation and store them in your freezer so they’re ready for you. Do the same with big portions of salmon and hearty veggies. Buy a lot of nuts, berries, and avocados. You’re going to be a garbage disposal after this race, whether it happens immediately or a few days after the race, so pre-stock yourself with healthy options, that way when you’re raiding the fridge for your tenth snack of the morning, you’ve got something other than Frosted Flakes (why are the Frosted Flakes in the fridge?). By all means, eat the Frosted Flakes, too, but if you’re going to eat like a vacuum, you might as well have some of it be healthy. I won’t tell you what “healthy” is, since it’s different for everybody, but I would at least suggest Googling “anti-inflammatory foods” and loading up on some of those.  

Hopefully some of this has been useful! If I haven’t made it clear, race nutrition is a personal process of discovery, but it can be expedited by talking to people and hearing their strategies. Take a bit from different places, and don’t be afraid to experiment!

Comment below or send us an email at with any questions, tips, or tricks you may have for Kris or other Chaskis. Happy running!

— Kris Brown
— Tyler Andrews
— Ashley Brasovan
— Pete Kostelnick

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