Fight the Bonk Part II: Pepper’s Magic Marathon Nutrition Formula

The finish of the 2007 Flying Pig Marathon. Not quite a bonk, but close.

I can honestly say in my 24 marathon finishes (these include races, pacing, and a few trail marathons), that I have never been a victim of the infamous marathon bonk. The closest I have ever come was at the Cincinnati Flying Pig in 2007. For whatever reason that day I did some really stupid things with my nutrition and suffered major stomach issues after the race. I remember hitting some tiny incline around mile 24 and after having been on pace for my goal all day I watched it slip away.

Determined not to let that happen again, I researched like crazy and devised a nutrition plan based on the information I found. Because I’m a big geek, I came up with a mathematical formula to calculate exactly how many calories one needs to take in during the marathon to prevent bonking and minimize GI distress.

Are you ready to see how many calories my magic math says you need to take in per hour of your next marathon? Well get your calculators and come along and see!

Marathon nutrition comes down to preventing two things: 1) bonking and 2) GI distress. In other words, when coming up with your race day nutrition strategy you need enough calories to provide the energy you need to cover 26.2 miles without upsetting your stomach.

I found it hard to believe that everyone’s consumption would be the same, and while the general recommendation of a gel every 30 – 45 minutes seems a good baseline, I think it generally causes people to overconsume gels and thus get into GI distress territory. In my experience, custom designing your nutrition plan using my magical math formula has resulted in no stomach issues and sustained energy throughout my best marathons.

Alright, let’s get to the good stuff. Here’s the formula to determine how many calories you need to take in during your next marathon!


Weight  x  .63  x  GMP  x .3  =  Amount of Calories to Consume per Hour of the Marathon 


The Dreaded Scale! Don’t worry, this is just a measurement for optimal fueling! (Photo credit: vividBreeze)

Ok, let’s explain!

Step 1! What is your weight in lbs.? This is the “Weight” in the formula.


Step 2! The .63 is used to determine how many calories you burn per mile of running. You multiply your weight x .63 and this tells you approximately how many calories you’ll burn each mile of your marathon.


Step 3! Now we need your “GMP” or goal marathon pace, but in miles per hour (like on a treadmill). Here’s a calculator for converting your pace to miles per hour.


Step 4! When you multiply the first three steps together, you get the amount of calories you burn per hour, but when you’re running you can only replace/digest at most 30% of those calories. So now we need to take 30% of our calories burned per hour and this is our target calorie intake per hour of the marathon! We’re done!


Let’s do a quick example. Say Jenny is 130 lbs and plans to run a sub-3:30. A sub-3:30 is about 8:00 pace or 7.5 mph. Here’s how the math works for Jenny: 130  x  .63  x  7.5  x  .3  = 184 calories per hour.

My gel of choice! Image via

Remember, this formula tells us how many calories we can digest and use in race, at most! So if in doubt, err on the side of taking in a little less, especially if you are prone to GI distress. Jenny would probably be best off rounding down to 150 calories per hour, so taking a gel every 40 minutes, or 5 miles in her case, would be about right.

Conveniently most commercial gels have 100 calories per packet, which helps make the math easy when it comes to deciding what to take to get in those calories.


Additional Notes!

When to take your last gel. Remember gels don’t “kick in” for 30 minutes, so consider that when deciding when to take your last gel in the race.

There are 50 calories per 8oz serving of Gatorade. Image via wikipedia.

– To sports drink or not to sports drink? I do not take any sports drinks on the course. I am getting all the sugar I need from my gels. If you do take Gatorade rather than water, you would need to adjust the timing of gels if any to figure out how many calories you want to take in at each aid station. This obviously makes things trickier, but if you can’t stomach a whole gel at once and prefer your calories liquid style, it is easy to adapt the equation to your needs.


What marathon day nutrition plan do you use Salty Readers? Do you have a stomach of steel and can consume more than 30% of what you expend? Are you lucky enough to never have bonked in a marathon? Share your tips for nailing race day nutrition!


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A gal on a mission to save Cuyahoga County streams one storm water facility at a time. An ex runner of many facets including marathons, pacing, ultras and more. Chronic left side issues have me cycling more than running these days but I'm attempting to get back to my running roots.

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  1. Interesting! Using my last marathon’s weight and goal gives me 167 cal/hour. That is pretty close to the gel every 5 miles in your example which is what I was using. However, I remember feeling really “uck” and not wanting to take my last gel.

    I don’t feel like I’ve ever bonked in a marathon. Any second half fade that I experienced was due to injury.

  2. I wrote about the same topic back in January, based on a podcast interview Jay Johnson did with Trent Stellingwerff of the Canadian Sport Center – Pacific – The conclusions were about the same as yours regarding calories / hour that you can absorb, though he gave a flat figure versus weight-based (perhaps he assumed a “typical male runner” or something of the sort – I don’t recall him being specific about this). Frankly, I prefer to consume the calories via Gatorade to spread them out more evenly over the hour, though I don’t get precise about the amount I’m taking (as it would be difficult to do so given my unpredictable, umm, yield in actually getting Gatorade into my mouth when running).

    1. Also keep in mind most sports drinks at races are made from a mix, so the amt of calories will vary depending on how dilute they made the mix. Plus, good luck getting in even 4 oz out of a cup on the run as you say!

      1. I honestly don’t think you can “strictly” fuel your way to avoiding the bonk, by the way. Avoiding the bonk comes from training – getting used to running on little fuel by runs of 90 minutes or more, preferably before breakfast. A topic I’m particularly passionate about. To me, the best approach is to become as insensitive as possible to the specifics of your race day fueling, so that you can handle a variety of situations. For example, at Akron two years ago, I twice had a “bad exchange” on grabbing gels from volunteers and didn’t want to go back, so had to go without.

        1. You know you’re preaching to the choir here. That’s why this post is called Fight the Bonk Part II. It’s part of a comprehensive strategy to avoid the bonk!

  3. I’d like to know a little more about the stat ” can only replace 30% of the calories.” my very simplified way to determine kcal intake in a marathon is: the body stores about 2,000 kcals of energy in glycogen. I burn about 100 kcals per mile. Therefore, to stay ahead of the glycogen depletion, I try to take in 6 gels in a marathon. I also drink water and Gatorade, usually 2:1 (2 stops water, 1 stop water). I haven’t ever had GI issues and the only “bonk” i had was a result of a beginner’s error of poor race plan/pacing. I don’t math or stats to back it up but it seems to work for me (n=1).

    1. Since no one else is answering, I’ll chime in – I don’t know about the “30%” but the limitation you face in taking in carbohydrates/calories during a race is that most of your blood flow is directed into feeding your muscles (providing oxygen needed to convert glycogen/fat into energy). This leaves very little for digesting food, thus you are limited in the amount of calories that can actually make it to your muscles. You may be able to “stomach” 6 gels in a marathon and some Gatorade, but not all of it may be actually useful. However, if it’s not causing you GI distress, then there’s no harm in doing so, your body will process whatever amount it can (and save the rest for later).

    2. Sorry I have not been connected! Greg is right, the 30% is based on the fact that while running at marathon intensity only so much of your energy can be used to digest food. If you have a strong stomach you could probably eat more and not be bothered if you aren’t digesting it all, but as far as what energy your body actually gets to tap into and use it’s about 30% of what you are using. You just can’t replace everything you are using while your body is using most of it’s energy to propel you forward.

  4. Great post! Definitely saving this one for when I get to marathon distance. I’ll have to share it with my husband, who’s running the Marine Corps Marathon next month. I’m not sure he has a strategy besides “run fast.”

  5. This formula seems sound and getting carbs while running is something I really need to work on. A couple of things to consider about getting more carbs in:

    1.) You can get carbs into your system about 10 or 15 minutes before the start so you can draw on this right away.
    2.) Take a page from the cycling pros (No, not EPO use). As I was watching the La Vuelta a couple of weeks ago I noticed that Contador was taking gels on a consistent basis. He even took them on the climbs near the end to prevent bonking. This leads me to believe that it takes less then 30 minutes to realize the benefits. Cyclists whom race the grand tours are experts at glycogen replacement.


    1. Pepper actually wrote about how she takes a gel 20 min before the start but her cranky editor removed it to simplify the post! And any marathon runner’s whose stomach can handle carbs that late in a race might as well try. I have never been there! Thanks for stopping by, Dave!

    2. I use a gel 15-20 minutes before with a swig of water and even if i don’t see the benefits of a gel towards the end of the race I believe it helps with post race recovery to never be fully depleted if possible! Like Salty said that got cut from the post to simplify!

  6. per my own physiology, as mostly a distance trail runner, gels are generally anathema. they are just too sweet. i would rather a few bites of a sandwich! my stomach automatically starts grumbling between 40 and 50 minutes during even short runs and gels just don’t cut the mustard. %^) as a result, i tend to grab one Gatorade and one water from most of the aid tables and only resort to gels as a method for getting caffeine into the system.

    that being said, i definitely notice a potentially placebo effect of taking in a gel or any sugar almost immediately when i’m pushing really hard. during speedwork is a great example of noticing a huge pick-me-up when i’m starting to feel a heavy fade almost immediately in the next repeat.

    i am certain we can all agree that the #1 rule of fueling is to experiment with your business BEFORE the race and not screw around with gel X or Shotblocks if you’ve never done so. ;^)

  7. Ok Pepper,
    I am aiming high for a PR by maybe 6-7 minutes on my half marathon this coming up weekend. I am not uber fast like you all, but am hoping for a 10:30 (or less!) pace. I did your calculations and it came out to 188. Decrease to 150 to prevent gut rot, and I am wondering would you recommend a GU and a Half at once? A GU and some beans? Spread them out a few minutes? So far in all my training I haven’t had stomach issues thanks to not mixing it up with sports drinks! I made the mistake in my last half to GU and Gatorade and was grateful I didn’t yawn in technicolor during the last 3 miles! Any advice you can offer I would appreciate! Thanks!!

    1. Diane, I think if you take 1 gel 20 minutes before your race with some water then 4 gels total would be perfect. Aiming to take your first 20 minutes pre race, your next 20 minutes into the race (40 minute intervals), the next an hour into the race and the last at an hour 40. If that sounds like too much for your stomach I’d cut down to 3 and aim to take them starting 20 minutes before and every 50 minutes thereafter.

      If you go with 40 minute intervals, then that should line up relatively close to your miles 2/3, 6/7, and 10/11. If you go with 50 then miles 3/4, 8/9.

      I think spacing the gels out rather than trying to take more than 100 calories at a time would work best! And definitely with you on avoiding the use of gatorade with gu!

      Good luck! I hope you smash your PR!

  8. Hi, I have started running again after many years of “standing still”. I am looking to do a 1/2 marathon in Oct, followed by a full marathon in January. I am only using dex4 sugar tablets when doing long runs (2 hours) at marathon pace. Any thoughts on the sugar tablets. I am 55 years old. Thanks in advance 🙂


    1. Hi, James! Cinnamon here. Two hour long runs at Marathon Pace!? That sounds like a recipe for overtraining to me… But let’s get to the tablets.

      I’m just curious, have you considered that sugar tablets are not necessarily the ideal nutrition for marathoning? They don’t contain any salt, which is an essential ingredient for fighting the bonk. Not only that, these particular tablets seem to contain a high concentration of acids, which could potentially hurt your tummy.

      Most trustable (non-commercial) research seems to indicate that all nutrients are better absorbed through more whole food, so from what I know, you may be limiting the effectiveness of the sugar you’re ingesting by using tablets instead of a more food-like option.

      What I really wonder is WHY are you taking the tablets in particular? Is it because of the expense of gels and sport nutrition? Because you don’t really need to be taking them as often as the packages say, as Pepper noted in this post, and as my sister Salty has written at length. Is it convenience? I find it hard to believe that these pills are more convenient than, say, a Clif Shot or the Jelly Belly Sport Beans. Is it because you have an aversion to gels or other sport-nutrition items, or worry that they’re bad for you? If so, I understand; they make me feel sick, and I’ve written extensively here on Salty Running about my journey toward finding the perfect fuel option (I can’t say enough about the Feed Zone Portables book for teaching me about in-motion nutrition). But honestly, I don’t think these tablets are any better for you than the gels. They might taste a little better, but if so it’s probably only because of the salt in the gels, which is a mineral you need if you’re trying to maximize your performance!

      I’d love to hear back from you – what prompted the sugar pills in the first place? What do you think of my answer?

  9. I am preparing for my first 50-mile ultra in April and have been trying to find information on how to prepare for that sort of distance when it comes to fuel for the body. This article is helpful as a starting point, but can you offer any further insight on the caloric makeup to be consumed? (i.e., how much/percentage of sodium/carb/etc.)
    Based on the formula given, I’d need to consume around 200-250 calories per hour. I don’t drink sports drinks and the prospect of consuming that many gels is not very appealing. Thanks in advance for any feedback!

    1. Hi Kyle, I have not really researched this but it is a great Ask A Salty Question which I will forward to the group. In general I think mostly card with a little protein would be your best bet. You can do fruits instead of gels or snacky stuff like chips or cookies if your stomach can tolerate it. PB sandwiches also work great.

  10. Thanks for the formula! I just don’t quite understand it. It seems like the slower run/hour, the more calories you need to consume. For example, according to the equation, if I run A 10 minute mile I would need app 280 calories per hour, whereas if to run a 9 minute mile I would only need 250. Don’t you burn more calories by running faster?

    If you could explain that would be awesome. Thanks!

    1. Hi Angela, You actually burn the same amount of calories per mile, but not per hour. If you are running 10 minute pace at 120 lbs your Goal Marathon Pace is 6 MPH and number of calories per hour would be 136. At 9 minute pace your GMP is around 6.65 and your hourly caloric intake is 151. I think you just forgot to convert minute per mile into miles per hour!

  11. Hi.
    Enjoyed the read and advise.
    Would the same formula work for kilograms and kilometers?
    I am 68kg, run a marathon at 6 minutes per kilometer.

    1. Yasien it would work the same but you would need different conversions! TO be safe convert 68 kg to lbs = 150 Lbs and 6 minutes per km to miles per hour = 6.214 miles per hour so 150*.63*6.214*.3= 176 calories per hour

  12. I weigh 280lbs and run roughly 12mins per mile how many calories would I burn over the distance and what kind of calorie intake would I need it just seems this calculation is a little too simplistic what I mean is if because im a lot heavier and I’m working a lot harder I’m going to burn more calories surely for e.g my average hr on my last half marathon was 158 as I get fitter my hr per hour decreases and as such I could run the same distance in the same time but because my fitness has improved my hr will be lower as is my energy consumed and therefore gels needed I occasionaly run a speed that I ran 1 mth ago to see if I’ve improved and to see the the calories burned in the most recent exercise tally with the run I did the month before same speed same distance and although my weight would have not shifted much my fitness has increased and my calories burned would be 15-20% lower therefore using your method by just weight alone isn’t that flawed when you get to much heavier runners than the 140 or 150 lb runner?

  13. Sorry to be a little off tic, but does anyone know if Gu or any other gels happen to be dairy, soy and gluten free? I love my allergen-free gummy bears, but they don’t seem to do anything on long runs. Thank you for your help 🙂

  14. Have you found that this formula works for all body shapes and sizes? I’m a 6’2 runner, weigh 175, 38 years old. I’m in very good shape but because of my muscular build I sweat a lot more and burn more calories than most guys. I tend to need about 15-20% more water intake than most stock calorie/water intake calculations come up with. Do you think your formula would work for a guy like me?