Fueling for a 100 Mile Running Race

Nick ClarkFueling for a 100-mile running race through the mountains is not only an enormous feat athletically, it poses great obstacles nutritionally.

Ultra runners typically race between 18 hours and 30+ hours in order to accomplish this feat and do so with little or no sleep at all. This means running through the night often at high altitude and through a wide range of temperatures.

The famed Western States Endurance Run from Squaw Valley to Auburn California climbs 18,000 feet before descending nearly 23,000 feet. Runners endure temperatures ranging from the high 40’s to over 100 degrees through the course of a single race. These enormous variances and distances pose issues physically, mentally and nutritionally.

Runners Face Unique Nutrition Requirements

It is well established that the act of running due to its jarring up and down movement reduces an athletes ability to absorb nutrients versus events like xc-skiing or cycling. Runners must also carry much of their nutrition and fluids between aid stations that at times can be hours apart.

Athletes have just two to three hours of glycogen stored in their muscles and liver.

It’s also well known that athletes have just two to three hours of glycogen stored in their muscles and liver.  Once this glycogen is used, athletes enter the dreaded bonk zone. There is no one perfect nutrition plan for ultra running, in fact our runners vary considerably in their nutrition plans, however there are some consistencies that can offer a greater chance of success when planning out your racing nutrition needs.

We have asked our eight elite ultra runners to map out their nutrition plans for 100 mile running races. Understand these are ultra runners with many years of experience, meaning their bodies have adapted to the rigors of running 100 miles.  They bring both experience and also a physiological adaptation that can only be developed over many, many seasons of running. Even for these elite runners it takes years before they finally nail their nutrition.

Duncan Callahan put it best “For many years, a poor fueling strategy significantly hindered my ultra-running performance.  I felt like a blind guy playing darts – bouncing from idea to idea and ‘wishing’ that something would work. Beginning in the fall of 2009, I went on a research quest to find a nutrition system and plan that would work for me.”   That year Duncan won the prestigious Leadville-100 on EFS electrolyte drinks.

Ultra Running Nutrition Plans

Below is a list of our elite ultra runners with some key attributes of their running nutrition plan.


Duncan Callahan
2X Leadville 100 mile champion
Detailed Nutrition Plan
-Large breakfast (1,400 calories) 2 hours before the race
-Sip on EFS leading up to race start
-240 to 360 calories/ hour
-Majority of calories from EFS
-If really hungry ‘warmed mashed sweet potatoes’


Krissy Moehl
Ultra Trail du Mont Blanc Champion
Detailed Nutrition Plan
-Same breakfast before every race: Oatmeal PB & J, 2 hours before the race
-EFS liquid shot every 30-45 minutes
-PreRace every 2-hours
-Nibble on Clif Bar or potatoes to feel satiated.


Luke Nelson
2nd Place 2012 Wasatch 100
Detailed Nutrition Plan
-Ultragen, Tortilla with Nutella 2 hours before the race
-Sip on EFS liquid shot with PreRace leading up to start
-300 calories per hour
-Sip on the Luke Nelson Slurry (1 scoop EFS, 1 EFS Liquid shot in a 10oz bottle topped off with water)
-Nutella and Jam wraps as solid food at aid stations
“The last 50 miles are the crux when it comes to fueling.  It is the most critical time to keep the calories flowing, but for me at least, my stomach isn’t too excited about anything.  I do well by keeping it simple and keep taking nips of the slurry.


Matt Hart
2012 Tahoe Rim 100 Mile champion
Detailed Nutrition Plan
-Breakfast 2hrs before the start: hard-boiled egg and a banana, Yerba Mate tea
-EFS liquid shot or Luke Nelson’s Slurry every 30-40 minutes (consistent small nips of fuel)
-I try to eat small amounts of real food consistently throughout the day to avoid that hollow feeling; fruit, yams, raisin-almond-coconut balls, avocado wrapped in turkey.


Nick Clark
Wasatch 100 Champion
Detailed Nutrition Plan
-Breakfast of donuts, bagel and coffee 2 hours before the race
-Hydrate with EFS leading up to start
-10-30 ounces of EFS drink every hour and EFS liquid shot flask every three to four hours
When it’s cool I drink less total fluid and consume more EFS liquid shot.  When it gets hot I rely more on EFS drink.
-Mostly fruit at aid stations


Scott Jaime
50K USATF Masters Champion 3.13
Detailed Nutrition Plan
-In cool temps 20oz bottle with 200 calories EFS liquid shot
-In hot temps.  1st 20oz bottle with 200 calories EFS liquid shot and water  2nd 20oz bottle with 100 calories EFS grape.


Darcy Africa
1st Bighorn 100 CR
1st Hardrock 100
1st Bear 100 CR
Detailed Nutrition Plan
-200/300 calories per hour
-Don’t change up breakfast: oatmeal, banana, and coffee
-Always carry 1-bottle EFS and 1 bottle water during entire race
-Take OptygenHP after 50mile mark
-Carry EFS LS Kona Mocha, a bar and honey stinger chews


Karl Meltzer
34 – 100 Mile Ultra victories
Detailed Nutrition Plan
-250/350 calories per hour
-80% from EFS LS and 20% from EFS drink
-A few RedBull drinks, Honey Stinger
-Potato soup, Boullion and if hot SaltStick caps


Tips On Developing Your Running Nutrition Plan

Your pace determines what ratio of glycogen to fat you burn

The most overlooked element of nutrition for many runners is pace.   It is your pace that determines what ratio of glycogen to fat you burn.  As you approach anaerobic, high HR efforts you begin to burn almost exclusively glycogen for which you only carry a 3-hour supply.   At moderate aerobic efforts you burn primarily fat, for which you have plenty to last days.

Run or walk aerobically all day and you should be able to keep up with your demand for glycogen.  Pacing usually fails on that first climb when everyone is together.  Stick to YOUR aerobic pace.  If you go anaerobic you immediately start burning your glycogen and can, very early on, initiate a bonk.  Remember that at altitude your heart rate will be elevated 10-20 beats higher, this means you have to slow the pace even further to get to your aerobic level.

-Breakfast 2 hours before (eat what you are accustomed to, though focus on carbohydrates and if possible gluten free carbohydrates).

-Pre-hydrate with an electrolyte fuel drink like EFS

-Consistent fueling, sipping drink every 5-10 minutes.  Don’t get behind.   Most athletes will need 250-350 calories per hour, though only you can determine your exact amount.   Wasatch 100 champion Nick Clark through years of adaptation prefers to run on minimal calories.   Its important athletes know what they can handle and choose an appropriate caloric intake goal.

-The majority of calories should come in liquid form.  This offers hydration and superior absorption.  Being hungry is OK.  This means your stomach is empty which means the fuel you are consuming is going to your muscles.  *First Endurance does endorse the concept of fueling an entire Ultra on liquid alone.  Few practice this, though the elite runners do tend to have fueling strategies that have far more liquids than solids. 

-Limit solid foods and spread out evenly in small portions.  Solid foods can back up your system if you are not careful.  Consume them with adequate water.

-Solution percentage should change as temperature changes:  Hot temperatures mean you can consume a minimum of 12oz fluid for every 100 calories.   In cold temperatures you can consume a minimum of 12oz fluid for every 200 calories.

Solution percentage chart

-Have contingencies built in.

a) If stomach gets upset or sloshy, go to straight water, or nothing at all.

b) If ‘very hungry’ take small amount of solid food.

c) If cramping go to water and very salty snack (pickles) or sip on EFS  drink at an 7%-8% solution.


Remember that proper training will give you the fitness to get to the finish, but poor nutrition will prevent you from getting there.   Not only should your training plan be meticulous, so should your nutrition plan.

The first step is to have some semblance of a plan and practice it during your training.   You can choose different race nutrition segments to practice on different run occasions, i.e., pick three different breakfasts of varying nutrients and calories and see how you feel going on a long run two hours post breakfast.  Learn what works for breakfast,   then move on to determining what concentration you want your calories at varying temperatures.

If you’d like to give our First Endurance products a try risk-free, click here for our new customer discount.

17 replies
  1. Ultrarunninfool
    Ultrarunninfool says:

    First off Thank you Robert! 3 1/2 weeks ago I started on First Endurance products. EFS sport drink, liquid shots, optygen HP and Ultragen. Being an ultra runner it’s always really hard finding the right nutrition for long training runs and long ultra races. I used every product under the sun and nothing seem to work well especially past the 50k mark. So I recently stumbled on an article about Karl Meltzer and saw he uses this product called First Endurance. So I went onto the web site and watched every video of every product. After watching the videos I found all the FE products at my local Triathlon shop and picked up EFS drink, liquid shot, optygen HP and Ultragen. The next day I went out on a 21 mile training run using EFS drink and liquid shot and can I tell you I was amazed. I had so much energy, no gasy feeling and didn’t feel hungry. Well 3 weeks later, very last minute I decided to enter The Double Top 100k ultra in Northern Georgia, 3 days before the start. I had emailed Robert and after about 10 emails going back and forth he helped me dial in a proper dosage of calories I should be taking in for my size, weight and ability for the 100k. Im 6’1 195 lbs. Well he hit the nail on the head. I mixed 1 scoop of EFS to 5 oz’s of water, so I mixed 4 scoops to a 20 oz bottle which was a 2 hour bottle, also included sucking on 1/2 a liquid shot flask for that 2 hours. That gave me 600 calories for every 2 hours (300 calories an hour). That was the magic mixture for me. I had never trained with that mixture, Robert basically gave me that as a ball park and I went with it. Amazing! Never did I feel hungry, never had low energy, energy was always high and I could basically blow through the aid stations only having to grab a little water.
    Every time I came through the aid stations all the aid station volunteers were blown away that I wasn’t taking in any food, just water. They would say “what are you eating then” I would say , drinking First Endurance and I mean every aid station would ask that.
    The 100 milers took off at 3am and us100kers took off at 6am, mind you at the start it was dumping snow. It was snowing unexpectedly the night before and during the whole race, temps never got above 28 degrees. We all took off and by the 21 mile aid station I had about a 1 mile lead on second and was feeling so strong even though the weather was absolutely horrible. I got to the 31.5 mile turn turnaround at 5hrs 50min. This race had over 20,000 ft of elevation gain and never once did I feel sluggish, on my way back from the turn around I checked my watch and passed by the second place runner 3 miles later which gave me a 6 mile lead cause he still had 3 miles to the turnaround. Well I got to the 42 mile aid station and got some bad news from one of the aid station volunteers, I rolled in feeling great and was told “your not going to believe this but they have to call the race” I said call it how? They said they have to stop the race, the conditions are so bad at the upper aid stations they can’t get aid to the 100 milers do to the snow and ice. I’ve never felt so deflated, with over a 6 mile lead, feeling so strong and knowing I was going to win the Double Top 100k, I was truly bummed. So I got a ride back to the start/finish line where we all were in a cabin, I had so many volunteers who were also ultra runners ask me. What in the world do you eat and drink??? I told so many people what it was “First Endurace” they all said I’m going out on Monday and buying what ever it is you are using.
    So all I want to say is not only Thank You to Robert but how amazing First Endurance products work. I am so over the moon about these products and I have now found the nutrition that works for an avid ultra runner.

  2. Matthew Van Horn
    Matthew Van Horn says:

    When these guys say they mix liquid shot with 10-12 OZ water, do they mean they dump the entire 400 calorie flask into the water bottle?

  3. Ultrarunninfool
    Ultrarunninfool says:

    I did have on a Ultraspire Revolution racing vest, so I carried 2 20oz bottles of EFS, a 26 oz bottle of water and always had 2 liquid shot flasks with me. Our drop bags were at the 21 mile aid station. So carrying the 2 20oz bottles, 2 liquid shot flasks and filling my water bottle up at every aid station would give me a range of about 25 miles. Especially with how much climbing there was during this race that amount worked perfect. Thanks again FE! Richard

  4. Ultrarunninfool
    Ultrarunninfool says:

    Oh yeah! Within 30 After every training run and after the 100k…It’s cappuccino Ultragen! Amazing how great I Feel the next morning, that stuff really works.

  5. First Endurance
    First Endurance says:

    YES. You can mix EFS liquid shot in a water bottle. Unlike other gels it goes into complete solution.

  6. Ultrageek
    Ultrageek says:

    Really like efs but it gives me the shits after about 10hrs. Not sure it’s a complete fueling system. Interested to read about what other ultra runners do.

    • Robert Kunz
      Robert Kunz says:

      @Ultrageek start tracking your solution % on long runs.   Track how many total calories your consume and how many total ounces of water you consume.   More than likely your gastric distress is due to a concentration of calories that is too much to handle.

      • Ultrageek
        Ultrageek says:

        @Robert Kunz good comment. generally try for about 300 calories/hr and 700ml of water/hr. with other products this seems to work. Eating liquid calories for 12+hrs creates gas issues but only had other issues with efs. Really like the product just this issue is pushing me away from it.

        • Robert Kunz
          Robert Kunz says:

          @Ultrageek  @Robert You can read by each athlete what they do for their long distance racing.  The main theme is using EFS, limiting other foods and drinking enough water to assure all items get absorbed.   Are you also eating food on your long runs?

        • Ultrageek
          Ultrageek says:

          @Robert Kunz  @Ultrageek  @Robert Hi Robert,  could send you a fueling plan send me a note at ultrageek@shaw.ca. Would appreciate your help.  Generally hemp seed and yogurt for breakfast before the race.  EFS and water through the race.  Maybe a basic ham/cheese sandwich but generally don’t like trying to chew stuff while running.  My stomach is fine but end up in the bushes numerous times later in the race.  Other fuels have give me gas that’s it. And understand how my body reacts to over fueling or under fueling. Can’t believe I’m writing this on a public site.  Would love more of your thoughts.

        • Robert Kunz
          Robert Kunz says:

          @Ultrageek  @Robert  We can do this privately via e-mail.  Once you make the changes, please test it and post results here so at minimum our readers can read about the results.

  7. su
    su says:

    Hi, I have just read about First Endurance and would like to give it as try. I am running my first . 100 miles in May and I am really struggling with my nutrition atm.Would you kindly be able to advise me as to ratios/amounts I would need please
    I am about 5ft 4inch , weigh approx 54kg and I am 43yrs of age.At present I have been using perpetuem and by but I am not sure if by is a simple sugar and if it is I shouldn’t be mixing it with a complex carb? I have been given so much conflicting advice, I would like. To keep it simple and after reading your page, I thought First Endurance products sound great.I live in the UK.

  8. Henry osgood
    Henry osgood says:

    I live in Bellingham WA, who sells these products here, I haven’t found them yet

    Thanks, I’m 70 and according to ultra running no one over 70 has run under 24.

    I’m going to do a year build up to attempt sub 24
    When I’ll be 71. I’ve done several 50s in the 10’s, and I struggled with bonking, recovering and bonking yet again. Yet I finished strong.

    In one race in the alps I fell at 25 and broke my arm and still finished in 10:30.
    I read all the advice and know this will ne quite the ordeal but if i dont try, it certainly wont happen.

    Better to aim high and fail than aim.low and succeed.

    • Robert Kunz
      Robert Kunz says:

      If your local stores do not carry what you are looking for you can simply ask them to bring it in, or get our products directly from http://www.firstendurance.com.

      Good luck with your quest to go sub 24 hours. We are happy to consult with your nutrition plan to make sure you don’t bonk. This is typically a reflection of incorrect osmolality or concentration of your calories. We can help assure that does not happen.


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