Nutrition for Ultra-Runners Part #1 – Trending Diets


This is Part 1 of a 6 part series. 

Part 2 – Pre-Workout and Pre-Race Nutrition for Ultra-Runners 

Part 3- Post-Workout and Recovery Nutrition for Ultra-Runners

Part 4- During Workout and Intra-Race Nutrition for Ultra-Runners

Part 5 – Everyday Nutrition for Ultra-Runners

Part 6 – Training the Gut for Ultra-Runners

*While this blog was written with ultra-endurance athletes in mind, the vast majority of the information is also applicable to conventional endurance athletes.


There’s a lot of conflicting information out there regarding nutrition for…well, anyone and everything.   Whether your goal is to lose a few pounds, put on a few pounds, throw heavy weights around, run a fast 10k, or just eat for overall health and wellness, there is an overwhelming amount of “guidance” pulling you in all different directions.Unsurprisingly, this holds true for ultra-runners and other ultra-endurance athletes as well.  Some of the current dietary trends for ultra-runners and the like include:

  • Train-low, compete-high
  • Low carb/high fat and keto diets
  • Intermittent fasting/time restrained feeding/fasted morning runs

Sometimes it can be challenging to filter through what is scientifically relevant and what is “hype.”  The purpose of this blog is to help you see through some of the haze surrounding these topics.  Let’s start by diving into each of these dietary trends in a bit more detail.


Proposed benefit/goal Training with low carbohydrate and glycogen forces the body to rely more heavily on fat as its primary source of fuel.  This may lead to improved efficiency when using fat as fuel.

How to do it – There are a few different ways one could achieve training low.

  • Workout twice – The first workout effectively depletes glycogen.  After the first workout, very little to zero carbohydrates are consumed before the second workout, forcing the body to rely more heavily on fat for the second workout.  
  • Train on an empty stomach – This is easily accomplished by skipping breakfast before a morning workout.  The last meal ideally should not be within 8 hours of the workout.
  • Carb-free long efforts – Working out for extended durations with no carbohydrate intake during the workout.  If using this strategy alone (without #1 or #2), workouts should be a minimum of 2 hours to achieve sufficient carbohydrate/glycogen depletion and adaptation.  
Drawbacks of Train-Low, Compete-High for Ultra-Running

Drawbacks of not ingesting CHO after 1st workout (#1) – Ingesting carbohydrates immediately after exercise doesn’t just replenish glycogen.  Doing so also speeds up muscle recovery, improves immune function (Peake et al., 2016), and positively influences hormones (Nieman et al., 2003).  controlled cortisol is crucial for endurance athletes

Drawbacks of training fasted (#2) – Fasting may decrease body fat.  However, it breaks down lean mass as well, and there is minimal evidence to suggest improved performance (Zouhal et al., 2020).  Exercise in the fasted state also results in elevated cortisol compared to exercising in the fed state (Kim et al., 2015).   Elevated cortisol has many deleterious effects on athletes – increased muscle breakdown, and suppression of metabolism to name just a couple.  For more information on cortisol as it relates to ultra-endurance athletes, check out this blog.

Drawbacks of not consuming CHO during long efforts (#3) – The gut can be “trained” to tolerate increased carbohydrate quantities during exercise.  Training without carbohydrates during long workouts eliminates a golden opportunity to train the gut.  If one plans on “competing high,” their gut needs to be able to handle high amounts of carbohydrates during exercise.  Training low and then attempting to compete high may lead to various GI issues due to the gut not being adequately adapted to high amounts of carbohydrates during exercise.

Overall drawbacks of the train-low, compete-high method – Carbohydrates improve exercise performance during training.  Sure, an athlete may improve their ability to utilize fat as fuel using the above strategies, but does it make up for a lower quality training session?  Perhaps this is why the train-low, compete-high strategy doesn’t always translate to improved performance (Burke, 2010).


Proposed benefit/goal – Training with low carbohydrate intake and depleted glycogen stores forces the body to rely more heavily on fat as its primary fuel source.  This often leads to improved efficiency when using fat as fuel.  Additionally, a ketogenic athlete will often rely less on carbohydrates during a race, a key difference from the train-high, compete-low strategy.  Less reliance on consistent caloric intake during competition can benefit athletes who are susceptible to GI issues.

keto dietHow to do it – The ketogenic diet limits carbohydrates to 50 grams/day or less, the equivalent of about 2 apples.  A low carb/high fat (LCHF) diet is less defined, and there are countless variations.  For example, one might consider a macronutrient ratio of 40% carbohydrate 45% fat a LCHF diet, while another might aim to take in closer to 20% carbohydrate and 65% fat.  The main difference between the ketogenic diet and a LCHF diet is that the LCHF diet does not necessarily lead to ketosis, while the ketogenic diet does.  Ketosis is when the body turns fat into ketones to use as a primary fuel source.  This is a result of having very little glucose (carbohydrate) available to utilize as fuel.  Nonetheless, when it comes to endurance athletes adopting either diet, it is usually done so to increase efficiency utilizing fat as fuel.

Drawbacks of Low Carb and Ketogenic Diets for Ultra-Running

Compliance – A strict ketogenic/LCHF diet is a fairly restrictive diet.  In fact, when it comes to the ketogenic diet, many people who THINK they are in ketosis are not, and it has been shown in studies to have a high rate of non-compliance (Ye et al., 2015).

Cortisol – Carbohydrate ingestion during exercise reduces cortisol and epinephrine during prolonged exercise (McAnulty et al., 2007).  As previously mentioned, keeping cortisol in check is essential for endurance athletes; learn more about that here.  The combination of carbohydrates and protein post-exercise also has a favorable effect on cortisol.  Adequate carbohydrate intake is one of the most critical factors for keeping cortisol levels from becoming chronically elevated.  

Immunity – High carbohydrate diets have a favorable effect on immunity during times of increased endurance training (Costa et al., 2005).  

Recovery – Adequate glycogen replenishment from post-exercise carbohydrate and protein has a positive effect on muscle recovery (Ivy, 2004).  Removing carbohydrates from the equation diminishes glycogen replenishment, and consequently, muscle recovery.

Bone – There is a decent amount of scientific literature suggesting that a ketogenic diet may negatively impact bone health in the short-term (Heikura et al., 2020).  On the other hand, there are also longer-term studies that imply that bone health is not compromised (Bertoli et al., 2014).  Clearly, more studies are needed.  In the meantime, it is likely a good practice to pay special attention to bone health if following such a diet.

Explosiveness – Carbohydrate is the most efficient fuel source.  I didn’t say abundant; that’s obviously fat.  But carbohydrate is unarguably the most efficient, and as a result, a loss in explosiveness is often observed.  Although explosiveness per se is not a factor in most ultra-endurance competitions, many coaches agree that high-intensity training is beneficial for ultra-athletes for raising V02 max and lactate threshold.

Summary of the Science –   The science is clear that fat oxidation is typically increased when following these diets, thus achieving the goal of becoming less carb dependent and becoming a more efficient fat burner (Murphy et al., 2021).  However, this comes with an oxygen cost (Leverve et al., 2006).  Burning fat as fuel requires significantly more oxygen than burning carbohydrates  – likely another reason that becoming a more efficient fat burner in this manner doesn’t necessarily equate to improved performance. It is inconclusive whether or not a ketogenic diet is beneficial for endurance.  The current body of evidence suggests that there is little, if any, benefit for endurance athletes, with many studies showing an overall negative impact on performance despite significantly higher fat oxidation rates.  Of course, like most topics, some outliers suggest otherwise.  Some suggest the main reason that some see benefits is from the weight loss that often results.  Prior GI intolerance when consuming carbohydrates during exercise could be another reason some see improvement.


time restricted feedingProposed benefit/goal – Similar to the two previously mentioned diets, the main performance-related goal that people seek with any of these techniques is increased fat oxidation.  By running fasted you allow glycogen stores to become depleted, encouraging your body to utilize fat as fuel.

How to do it – It depends on which technique we are talking about, but they really are just different versions of one another.  An example of time-restricted feeding could be not eating from 8 PM to 1 PM the next day.  A fasted morning workout is simply exercising without eating breakfast.  As previously mentioned, this is also a technique used with the train-low, compete-high strategy.  Intermittent fasting is similar to time restrictive-feeding but might not follow a consistent schedule.  It could mean fasting entirely for two days/week, or it could mean eating normal 4 days and eating <500 calories on the other 3 days.  There are countless variations.

Drawbacks of Time-Restricted Feeding, Fasted Morning Workouts, and Intermittent Fasting for Ultra-Running

Muscle Breakdown – Studies suggest twice as much muscle breakdown during fasted runs than during non-fasted runs (Schoenfeld, 2011).  

Cortisol – Exercise in a fasted state leads to significantly higher levels of cortisol.

Intensity – Exercise intensity is impaired when working out in a fasted state (Terada et al., 2018).

Time to Exhaustion – When fasted, studies show that participants cannot work out for as long (Terada et al., 2018).  If training for long efforts, you need to be able to put in long efforts.

Science – Exercising in a fasted state (10-12 hours with no food) results in the body utilizing more fat as fuel in the workout.  Additionally, one starts to “tap” into their fat stores earlier.  In other words, one WILL use a higher percentage of fat during a fasted workout.  Unfortunately, most studies do not show any real performance gain from this, and some show a performance detriment.  This is likely a result of a combination of the drawbacks mentioned above. 


plant-based endurance athletesPeriodizing Carbohydrates – I plan to discuss periodized carbohydrate training in detail in another blog.  This is a slightly more complicated strategy that shows some evidence of performance benefit, but not necessarily more than a non-periodized, high carbohydrate diet.    

Vegan/Plant-based – Plant-based and vegan are also extremely popular among endurance athletes, and I plan to discuss this in detail in a separate blog as well.   Much of the time, following a 100% plant-based diet isn’t necessarily done with performance (as the only reason) in mind.  Often, one does so with additional motives, whether for animal welfare, environmental reasons, or what have you.  Nonetheless, a high-quality plant-based diet should be capable of providing everything an athlete requires for optimal performance if the athlete is willing to supplement. 


Here’s the good news…99% of athletes need not worry about incorporating any of the above strategies for improved performance.

The reason being, because unless you are an elite athlete that has squeezed every ounce of improvement out of yourself without drastic dietary modifications, it’s likely not worth the effort or the risk.  While the strategies listed above have been shown to offer physiologic adaptation, this adaptation usually comes with a cost.  The cost can be impaired performance (temporary or ongoing), impaired recovery between sessions, elevated cortisol, fatigue, and undesirable psychological and physical symptoms.  Additionally, it is still unclear whether or not the desired adaptations that athletes seek from these strategies actually translate to improved performance.   Generally, more studies are needed to determine this.

Before incorporating drastic dietary strategies purely for improved performance, you should ask yourself a few questions.

Have I done everything I can do in training?  Do you have the right amount of volume?  Intensity?  Variety?  Is your training program optimal?  This could be a good thing to discuss with a qualified coach.  Elite athletes aren’t the only ones who benefit from coaches, nor are they the only athletes who DESERVE coaches.  Anyone who wants to improve can likely benefit from a good coach.recovery

Have I dialed in my recovery?  Recovery is just as important as training.  Are you getting enough sleep?  If not, adequate sleep will do more for you than any of the dietary strategies mentioned above, without risk!  Are you finding time to relax between workouts, or are you chronically stressed?  If you’re constantly stressed, your body won’t recover as well between efforts.  You can read more on that here.  How about recovery nutrition?  Read all about that in part #3 of this blog series.

How’s my mental game?  It’s no secret that to be an ultra-endurance athlete, you have to be one tough S.O.B.   Mental toughness and pain tolerance are naturalmeditating endurance athlete consequences of endurance training (Pettersen et al., 2020).   There are also scientifically validated strategies to improve performance through mental exercises that go beyond mental toughness, such as meditation and visualization.

Are there things I can improve with my CURRENT diet and nutrition?  Before converting to a restrictive diet, you might want to take a CLOSE look at your CURRENT diet.  For the vast majority of people, there are plenty of improvements that can be made without going as far as eliminating a micro-nutrient, counting calories, or restricting calories to a specific time of the day.  Consulting with a qualified nutritionist or dietitian who specializes in sports nutrition can be helpful.  Understandably, not everyone wants to fork over the dough for such a service.  If this is the case for you, I highly recommend reading through all 5 sections of this series.


Diet is a controversial topic.  Keep in mind that the above blog was written utilizing my current knowledge of nutrition (M.S. Clinical Nutrition) and my interpretation of the scientific literature’s general consensus. Inevitably, whenever someone discusses such topics, someone says, “have you heard of the ketogenic runner, Zach Bitter?” or something of that nature.  Yes, of course, I’ve heard of the fastest man to ever run 100 miles, and I’m a huge fan.  AND, I’m in no way saying that he shouldn’t be following such a diet.  But you can’t pick an elite out because of their diet and make the generalization that everyone should eat the same.  That’s ignoring the science.  Additionally, one could counter by saying, what about Karl Meltzer (variety – meat, beer, junk food, veggies, lots of gels), Jim Walmsley (vegetarian, lots of pizza, beer), Scott Jurek (strict vegan), or Courtney Dewaulter (very little restriction whatsoever)?  This is an endless cycle that ultimately goes nowhere and only proves that someone can perform at an elite level with various dietary approaches.

Keep in mind that there is no one-size-fits-all diet.  THIS is why you see people accomplishing incredible things while incorporating a wide range of diets.  One thing to remember is that just because certain elites are eating in a particular way does not mean that is the “best” way for you.  If you feel like a switch is justifiable for any multitude of reasons, by all means, give it a shot, and I hope it takes you to the next level.   My goal of this blog was simply to help you understand the pros and cons as I see them.  Thank you for reading and don’t forget to check out the next section on optimal pre-workout and pre-race nutrition for ultra-runners.  

Disclaimer – Use common sense, and always listen to your doctor over a blog post. They know more about your personal health situation than anybody behind a keyboard. As someone who has a Graduate degree in Clinical Nutrition, I realize the variance that certain medical conditions create when it comes to optimal nutrition and supplementation. If you have underlying medical conditions, always check with your doctor before starting a new supplementation routine.


Aird, T. P., Davies, R. W., & Carson, B. P. (2018). Effects of fasted vs fed-state exercise on performance and post-exercise metabolism: A systematic review and meta-analysis. Scandinavian Journal of Medicine & Science in Sports, 28(5), 1476–1493., S., Trentani, C., Ferraris, C., De Giorgis, V., Veggiotti, P., & Tagliabue, A. (2014). Long-term effects of a ketogenic diet on body composition and bone mineralization in GLUT-1 deficiency syndrome: A case series. Nutrition (Burbank, Los Angeles County, Calif.), 30(6), 726–728.

Burke, L. M. (2010). Fueling strategies to optimize performance: Training high or training low? Scandinavian Journal of Medicine & Science in Sports, 20 Suppl 2, 48–58., R. J. S., Jones, G. E., Lamb, K. L., Coleman, R., & Williams, J. H. H. (2005). The effects of a high carbohydrate diet on cortisol and salivary immunoglobulin A (s-IgA) during a period of increase exercise workload amongst Olympic and Ironman triathletes. International Journal of Sports Medicine, 26(10), 880–885.

Heikura, I. A., Burke, L. M., Hawley, J. A., Ross, M. L., Garvican-Lewis, L., Sharma, A. P., McKay, A. K. A., Leckey, J. J., Welvaert, M., McCall, L., & Ackerman, K. E. (2020). A Short-Term Ketogenic Diet Impairs Markers of Bone Health in Response to Exercise. Frontiers in Endocrinology, 10.

Ivy, J. L. (2004). Regulation of Muscle Glycogen Repletion, Muscle Protein Synthesis and Repair Following Exercise. Journal of Sports Science & Medicine, 3(3), 131–138.Kim, T. W., Lee, S. H., Choi, K. H., Kim, D. H., & Han, T. K. (2015). Comparison of the effects of acute exercise after overnight fasting and breakfast on energy substrate and hormone levels in obese men. Journal of Physical Therapy Science, 27(6), 1929–1932.

Leverve, X., Batandier, C., & Fontaine, E. (2006). Choosing the Right Substrate. In Sepsis: New Insights, New Therapies (pp. 108–127). John Wiley & Sons, Ltd., S., McAnulty, L., Nieman, D., Morrow, J., Dumke, C., & Utter, A. (2007). Carbohydrate effect: Hormone and oxidative changes. International Journal of Sports Medicine, 28(11), 921–927.

Murphy, N. E., Carrigan, C. T., & Margolis, L. M. (2021). High-Fat Ketogenic Diets and Physical Performance: A Systematic Review. Advances in Nutrition, 12(1), 223–233.

Nieman, D. C., Davis, J. M., Henson, D. A., Walberg-Rankin, J., Shute, M., Dumke, C. L., Utter, A. C., Vinci, D. M., Carson, J. A., Brown, A., Lee, W. J., McAnulty, S. R., & McAnulty, L. S. (2003). Carbohydrate ingestion influences skeletal muscle cytokine mRNA and plasma cytokine levels after a 3-h run. Journal of Applied Physiology (Bethesda, Md.: 1985), 94(5), 1917–1925.

Ormsbee, M. J., Bach, C. W., & Baur, D. A. (2014). Pre-Exercise Nutrition: The Role of Macronutrients, Modified Starches and Supplements on Metabolism and Endurance Performance. Nutrients, 6(5), 1782–1808.

Peake, J. M., Neubauer, O., Walsh, N. P., & Simpson, R. J. (2016). Recovery of the immune system after exercise. Journal of Applied Physiology, 122(5), 1077–1087.

Pettersen, S. D., Aslaksen, P. M., & Pettersen, S. A. (2020). Pain Processing in Elite and High-Level Athletes Compared to Non-athletes. Frontiers in Psychology, 11.

Schoenfeld, B. (2011). Does Cardio After an Overnight Fast Maximize Fat Loss? Strength & Conditioning Journal, 33(1), 23–25.

Terada, T., Toghi Eshghi, S. R., Liubaoerjijin, Y., Kennedy, M., Myette-Côté, É., Fletcher, K., & Boulé, N. (2018). Overnight fasting compromises exercise intensity and volume during sprint interval training but improves high-intensity aerobic endurance. The Journal of Sports Medicine and Physical Fitness, 59.

Ye, F., Li, X.-J., Jiang, W.-L., Sun, H.-B., & Liu, J. (2015). Efficacy of and Patient Compliance with a Ketogenic Diet in Adults with Intractable Epilepsy: A Meta-Analysis. Journal of Clinical Neurology (Seoul, Korea), 11(1), 26–31.

Zouhal, H., Saeidi, A., Salhi, A., Li, H., Essop, M. F., Laher, I., Rhibi, F., Amani-Shalamzari, S., & Ben Abderrahman, A. (2020). Exercise Training and Fasting: Current Insights. Open Access Journal of Sports Medicine, 11, 1–28.

Leave a Reply

Your email address will not be published. Required fields are marked *