Fueling for Multiday Runs

March 5, 2021

Dear Chaskis,

How do I fuel for multiday runs and competitions? Can I rely on the trusty gas station stop to meet my nutritional needs?


Aspiring multiday runners who finally found a time to catch up on their podcasts

Part Four of our nutrition series brings us Chaski coach and crazy fast and accomplished multiday pro runner, Pete Kostelnick, with some nutritional guidance for multiday runs. Following suite with our previous fueling posts Fueling for 50K, Fueling for 50k to 100k, and Fueling for Ultras: 12-24 hours, Pete dives into nutritional best practices, timing, and strategy for long-haul runs.

Pete is one of the most accomplished multi-day athletes in history. In 2016, Pete became the fastest person to run across the USA, covering 3067 miles in 42 days (72 miles per day avg). Always looking for more, he then became the first person to run from Alaska to Florida, covering the 5,384 mile journey in 98 days, entirely self-supported (i.e., he pushed a baby stroller with a tent/food/water/etc).  Pete is also a stud at individual racings, having twice won the Badwater Ultramarathon and with a 100 mile PR of 14:04.

Chaski Coach Pete Kostelnick

So you really want to get away from it all and do some sort of race or FKT (Fastest Known Time) attempt that takes multiple earth rotations.  Hmm… okay.  Who am I to judge?

This is where you can really get creative, but also really screw up on nutrition.  The funny thing about multiday runs is that you probably have the widest variety of nutritional strategies in practice, but it’s also the “distance” where nutrition can’t be faked whatsoever.  Think of it as creating a rocket to go to outer space.  There just isn’t much data to go off of, particularly for the same person for similar efforts.  

You can’t just go out every few weeks to run across Montana and slightly adjust your nutrition strategy.  You might only get one shot in your life at such an incredible undertaking.  You have to go in with something but be more open than ever to your rocket blowing up on take-off, and still be expected to venture off into outer space.  Cautiously optimistic.  Always ready for things to get real.

Disclaimer: I’m not a nutritionist and can’t give you nutritional advice, but hopefully this write-up can give you a good framework to tailor your own strategy or consider things you may be overlooking or overthinking during a multiday adventure.

Before You Take Off

Let’s take a step back, first.  Going into a multiday run, you need to be healthy and having your body functioning at its peak.  Ideally, you did a nice long 2-3 week taper, you’re fit, but maybe also 3-5 pounds heavier than you were during peak training.  That’s great!  I’ve done six “multiday” runs ranging from 6-98 days, and in each one I don’t think I went in particularly skinny.  You may be retaining more water, too, if you’re not training as much anymore.  There is a good chance you naturally get hungry easily coming off a big training block, so simply eating the same as you would during training can be a benchmark in the week leading into the race.  

It also helps to be at least somewhat fat adapted, so your body isn’t reliant on carbs alone to continue chugging along.  A good way to train for this is to run in the morning or coming off a fast for some of your easy runs.  You don’t have to get carried away, though, since doing a lot of long slow training will already have your body burning a higher ratio of fat for fuel.

Chaski Coach Pete Kostelnick


As you start your big run, it can be tempting to want to bank some miles and get out ahead of others or really push that record FKT pace.  As a result, you find quick wins in the carbs to keep you rocketing with no digestive issues.  You might even think you’re the first person ever built genetically to just hammer through each future day no problem.  

Don’t fall for it! Even Yiannis Kouros, the Greek god himself, was human (to a certain extent) in multiday runs.  In the history of marathons, there have been maybe a tiny percentage of people that wish they had started faster.  In the history of multiday runs, there has never been anyone who wishes they went out faster.  

Although this is kind of getting into race strategy, if you force yourself into a well-balanced nutrition routine early, you’ll hopefully find yourself more willing to mix in some walk breaks and hold back as your body balances energy used to digest food with energy used to run.  In most single day ultras, the magic game changer is electrolytes—in multidays, it’s protein.  

Ideally, you’re getting a solid 20 grams of protein every three hours.  The form of protein doesn’t matter so much as the fact you’re getting a steady stream throughout the day to start muscle protein synthesis and decrease muscle damage.  

I might not quite be ready for a burger or turkey wrap three hours into a multiday run at 10 am, but I can certainly start thinking about a protein bar.  Since protein takes much more energy to digest than carbs or fat, it can also act as a good governor on your energy and speed to keep your pace honest early on.

Cruise Control

It shocks me both how under-prepared and over-prepared some runners are for multiday runs.  Some just go by feel while others stay calculated to the calorie with some scientific model.  In my opinion, if you’re getting enough protein and found a rhythm of replenishing 50-100 calories per mile run (overall) with food spaced out no more than an hour apart, you’re on the right track.  

I like to rotate 6-7 ~100-150 calorie foods every half hour such as bananas, rice krispies, peanut butter balls, protein bars, energy chews, stroopwafels, etc, as my “base” to stay on track—those fuels I feel most comfortable, with at least one or two having meaningful protein content.  From here, I can layer in meals every 5-6 hours, certain fun but messy treats like potato chips with avocados, and a quick hit of a sugary drink like soda if I feel like my stomach is working hard to keep up after a meal.

Day one is notorious for being that “let’s party all night” day, because you’re fresh and well rested.  It’s difficult to say how far you should extend yourself on day one in mileage terms due to the vast differences in goals, terrain, race/FKT duration, etc, but you probably don’t want to go overboard by more than 20-30% above daily average on day one before taking your first extended break/full sleep.  

For example, if you’re racing for six days and have a goal of 300 total miles, you probably don’t want to do more than 60-65 miles before your first real sleep break.  Your body needs sleep to help the recovery process, so getting in a big meal rich in protein, fat, and carbs can be a win-win to food coma town and recoveryville.  Hopefully this is within 24 hours of starting the run, and if an attempt of 10+ days, hopefully no more than 15 hours of time on feet.  

Some multiday runs of 2-3 days can allow for simple nap breaks in order to optimize distance.  However, races (or, more commonly FKTs) lasting more than 10 days really require at least eight hours or more of rest so you aren’t in a vicious cycle of always trying to keep up as your body breaks down and your pace slows down.

Chaski Coach Pete Kostelnick

What About Mixed Drinks, Electrolytes, and Hydration?

I’m not really opposed to drink mixes or electrolyte drinks like Gatorade, but I’ve found for me they can upset my stomach when my stomach is literally working non-stop for days.  I love electrolyte drinks during races lasting under a day where I’m sweating more or in a hot climate.  I prefer water with a side of soda as safer bets for multidays, with the occasional electrolyte pill or salt pill.  

Unless you’re running in warmer circumstances, the beauty of multiday runs is that you’re not pushing yourself that hard, and you probably have cooler temperatures for the majority of the 24-hour calendar.  There have been times where I only consumed about one ounce of water per mile covered (northern Canada), and there have been extreme cases where I was consuming nearly 10 ounces of hydration per mile (Key West).  

My best advice on hydration is to hydrate often, make sure you’re urinating often, and like food, be open to calling it quits on a particular cocktail if something isn’t sitting well.  I’ve found that coffee can make me jittery, but drinks like Mountain Dew and Pepsi can be great ways to get some caffeine and a sugar boost if it’s getting late and you feel good enough to knock out more miles.  

I do typically have an energy drink or two on hand, but I try to only rely on these in the final push.  You’re already asking a lot of your body!


There’s a lot of emotion tied to multiday runs.  I always say that no matter what, it’ll “be something”.  Once you finish, your body might hurt more than when it was in motion.  If you have to fly home, you’ll probably be moving around restlessly the entire flight.  You’ll be extremely sleepy but may still find it hard to sleep at first.  

The collateral toll mentally and physically is undeniable.

My best advice is to just know everyone feels off after something like this.  You’ll probably be hungry all the time for at least a week or two.  You definitely want to indulge in some delicious food, and even though you’re so sick of what you ate during the race, may find yourself snacking on it at the hotel or airport just because it’s available.  I usually donate or throw away any of my race fuel left over so I’m not tempted to graze on what is most likely something my body doesn’t need for recovery.  

Allow yourself some time to forget about running for a week or two—maybe try a new hobby, read a book, or get into a new show.  Going for a walk or a hike can be a great way to stay active while still letting your body get back to neutral.  If you were smart, you don’t have anything on the calendar for a while, so let your body tell you when it’s ready to resume play.

— Pete Kostelnick

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