Ultramarathons & Ketones – The Experts Speak

by | May 12, 2020

Q: A lot of pros are using ketone esters. Do they really work?

A: Not as well as one would think. Here’s why:

This blog will rely on several new reviews by the academic experts on endurance sports nutrition. These publicized reviews are de facto Position Statements of what we know now.

For decades, strong science and the normal practice of training and running in ultramarathons has focused on hydration and carbohydrates to push human performance to its limits. Here is the consensus of research right now: “Research outcomes suggest that daily dietary carbohydrates (up to 12 g·kg−1·day−1) and multiple-transportable carbohydrate intake (∼90 g·hr−1 for running distances ≥3 hr) during exercise support endurance training adaptations and enhance real-time endurance performance” (Costa et al., 2019).

But this knowledge is not exactly easy to apply in the field – as Costa et al. state: “Whether these intake rates are tolerable during ultramarathon competition is questionable from a practical and gastrointestinal experience.” At First Endurance, we know how challenging it can be to get your nutrition right. That’s why we designed our line to work as a system so there’s no more guesswork about what you should take and when. In fact, another recent review on ultramarathon nutrition (Tiller et al., 2019) lists Sports Drinks (hydration, carbs, electrolytes) as the first Food Suggestion to take during ultramarathons (Table 4, page 11). Costa, et al., recommend carb drinks during ultramarathons (Table 1 on page 5).

Back to ketones. Because getting enough carbs to fuel exercise performance is difficult, other fuel sources can be used to add to, extend, or even replace carbohydrates. Fat and protein metabolites (breakdown products) are the only other practical choice, and both are involved with ketone bodies (aka ketone esters).

Note that a ketogenic diet (high fat diet) is not the same thing as ingesting preformed ketone esters. Let’s look at where the science is right now on ketone bodies and ultraendurance performance.

In theory, adding ketone esters, which normally increase in the bloodstream during exercise, can increase the number of ways to make ATP, which keeps your muscles working and your brain working too. Here is what the experts have distilled so far:

Despite the potential efficacy of other ergogenic aids (e.g., ketone ester, MCTs, vitamins, etc.), there are limited data to support their use, and further research is warranted(Tiller et al., 2019).

In the world of science-speak, this is not a condonement. It leaves the evidence door slightly ajar in case future studies show something practical and significant (the “we do not want to have egg on our faces” mentality), and for researchers to get funding for more studies.

But if there was big merit in ketone esters during ultramarathons, it would have surfaced with a better evidence rating. We are looking for As, not Cs or Ds. Bs may be helpful in the right settings. This review listed B/C/D ratings for the whole lot of “…other ergogenic aids…” without specifying where ketone esters sat.

Looking a little closer at the human performance publications on ketogenic diets, they have so far flunked out for ultraendurance performance (Evidence statement (category B/C) by Tiller et al., page 7). One crossover study of supplemental ketone esters showed a significant performance enhancement for distance (2% average, P<0.05) after lab cycling for one hour at 75% VO2max, followed by a 30 minute go–as–far-as-you-can period (90 minutes total). (Cox et al., 2016). The amount of ketone bodies ingested was 34 grams, which was 40% of the calories provided (the rest was glucose), compared to 100% of similar calories from glucose. 3/8 subjects showed a notable increase in total meters cycled. While this is encouraging, the exercise setting is different from ultramarathons and may not apply to long exercise time periods. In less controlled, real-life settings, these experimental conditions will probably not be met by most users, which means blunting reproducibility of these findings in real life.

Also, the cost of 34 grams of the ketone ester used ((R)-3-hydroxybutyl (R)-3-hydroxybutyrate ketone ester) is expensive; 12 servings of HVMN ketone ester costs $350.10, or $29.17/serving. Each serving has 25g of ketone ester – which is only 75% of the amount used in the study.

Other studies of ketone ester supplementation and endurance exercise have found significant decreases in performance (Leckey et al., 2017; O’Malley et al, 2017; Prins et al., 2020). It is now apparent that supplementing with ketone esters is not the same as a long-term ketogenic diet for exercise performance (Shaw et al., 2020), and is perhaps even worse than null for performance benefits.

As of right now, adding small amounts (a few grams or less) of some sort of ketoester, along with carbohydrates, is not detrimental during long-term endurance performance. However, trying to replace carbs with ketoesters does not look promising for widespread use in ultramarathons or other long-term endurance efforts.

Too many problems have arisen:
1) High cost per serving ($29.17 for 75% of the amount used in the study)
2) Complexity of usage & dietary practices
3) Stability, supply, taste, gastric tolerability issues
4) Which ketoesters to use?
5) Bulk of human performance studies are not finding improvements in long-term exercise
6) There are downsides I do not want to get into right now for taking high levels of ketoesters/ketoacids that reach to the epigenetic levels of cells that, if persisted, would impair overall health, and of course, exercise performance.

There are a few Laws of Nature that, to me, at best, will always limit use of ketone esters during long-term endurance performance. This is not a fad to follow.

We’d love to hear from you. Tell us what you think or ask us a question in the “comment” section. If you found this article beneficial, please share it with a friend.


  1. Kerry

    I think it’s important to add that I assume research has also not been done on a female specific population throughout phases of the menstrual cycle? Especially important as current research in Keto diets (I know it’s not the same as ketone supplement), are detrimental to athletic performance in females.

    • Luke Bucci PhD

      You bring up a serious deficiency in human research. There is a difference between female and male humans, and that factor has made research focus on males. Recently, and rightly so, this disparity has been questioned, especially for new drug testing, and there is a trend to focus on females and males separately. Stating the obvious, menstrual cycle timing is one of those poorly known factors, as is hormonal milieu, metabolic fluxes, body size/composition differences, menstrual/menopausal status, and protection of reproductive integrity and safety in case of pregnancy. Because these factors introduce unknown variability in response, researchers like to narrow the variability in order to use as few subjects as possible to satisfy Power Analysis to determine subject numbers, which directly influences cost, complexity and time.
      In my human study career, I always tried to include both genders. I did not see a difference in results between the genders, but I was looking at all sorts of measurements, not long-term endurance performance.
      To get to your question, for ketoester studies on endurance performance, in fifteen studies (one was metabolic markers only), 27 out of 226 subjects were female. If only the performance studies were considered, there were 10 females in 181 subjects. No subjects were of menopausal age. I did not see if menstrual cycle timing was considered.
      You are right that there is a gap on this subject for long-term endurance performance in menstruating females.
      I did my part previously in conducting a study using only young women, and we did synchronize the measurements to the midpoint of menstrual cycles. So researchers are doing better!
      Thank you for the question!

  2. Matt Hanson

    I think this is spot on. Dr. Bucci, this is a fantastic review. I was shocked on the price of the product! I’d never paid attention to that before since it wasn’t a product I considered using. The studies mentioned here were great and I appreciated that you included the quality/grade of the research study and not just the findings. The one “positive” result for kentone esters with the 90 min cycling test got the gears turning a little. I would have liked to see a glucose/keytone ester mixture up against a glucose/fructose or any other dual sugar blend since research has been pretty clear that multiple sugars are beneficial than a single sugar. Based on some previous studies I have read, I would expect that more than 3/8 would have gone farther in a dual sugar trial. Perhaps one of those ‘areas for further research.”

    This is why I love FE so much, it is very much a follow the science not the fad.

  3. Walter

    Super interesting article and a fair assessment of where things are at presently.

  4. Luke Bucci PhD

    Spyros – In answer to your first question (if glycogen available are ketone esters beneficial?) we all need to understand what our bodies are trying to do during endurance exercise, metabolically speaking. Ketone esters are formed during exercise normally, and their levels are somewhat increased in the bloodstream. What the legacy research shows is that using ketone bodies (endogenous or exogenous) is always going on in the background in a lesser amount than carbs (mostly glycogen). Nature’s backup plan in case carbs run out, but not at the same level of intensity.
    Utilization of ketone bodies for cellular ATP production is a lengthier and more difficult metabolic pathway than for carbs, both in quantity and quality. And always will be. That fact forever limits promise of benefits during long-term exercise.
    The current research is showing that even if ketone bodies levels in the bloodstream are sky high, their utilization is not as good as replacing glycogen, and typical use (mirroring field use) is more often detrimental to performance, which is predictable when glycogen is available. And prolonged ketosis has technical issues which are not conducive to long-term health or performance.
    Getting to the field use of ketone ester supplements in TdF and other events and anecdotal reports of benefit is not proof of benefit. There is always a placebo effect in real life, and that is not factored into research studies – it is factored out. So doing anything that is perceived as a benefit will have some sort of benefit…for a while, but will dissipate sooner more than later.
    As for the reason to use ketoesters right now, it has chalkboard logic. But there is a bigger chalkboard that is not supportive of benefits in long-term endurance exercise performance. And the real-life technical issues are not conducive to efficacy. In my opinion, the practice of using ketoesters as ergogenic aids for ultraendurance is not ready for prime time, and because of how our bodies work, will never have more than a bit player role in long-term endurance performance.

  5. Spyros

    Nice detailed article on ketone esters Dr. Bucci. I have a question and would like to hear your opinion on it. -Is it true that once glycogen is available as a fuel source, ketones no longer offer any real benefit? And if this is true, what is your opinion/explanation regarding professional cyclists using Ketone Esters in Tdf, where they are not in glycogen-depleted state during a stage? Are they consuming ketone esters without a reason? Thank you in advance.

  6. Andy

    Good read and looking forward to seeing future posts on Ketogenic diet.

  7. Breanne Nalder Harward

    Fantastic post. Thanks for using current credible research to discuss that we don’t know enough yet to recc using ketone esters for performance. I’m a RDN and a professional cyclist so questions on ketones as fuel come up a lot. Energy from carbs and hydration with proper electrolytes continue to reign.

  8. Sterling

    Thank you for the detailed info Dr. Bucci.

    Your article mentions “Note that a ketogenic diet (high fat diet) is not the same thing as ingesting preformed ketone esters.”

    How does the research look for a ketogenic diet & athletic performance?

    • Luke Bucci PhD

      Sterling – that is a bigger topic so will be split into several upcoming blogs. Thanks!


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