Four years ago as I began to learn about Paleo, Primal, and ancestral health in an effort to optimize my training and health for obstacle course racing, I started to hear rumblings about a “magical” metabolic state called ketosis. Ketosis could be achieved by eating lower carbs, low enough that it would cause your liver to start producing ketones for the body to use as an alternate “super fuel”.
From an ancestral point of view we would enter a state of ketosis and produce ketones when we could not find food or the food we were able to find was very low in carbohydrates. Ketones, produced by breaking down fats in our body, provided our ancestors a fuel source to use while we continued to search for food.
Today most people rarely enter a state of ketosis because there is always plenty of food around, especially carbohydrates. Recently though, keto has gone mainstream because in order to enter a state of ketosis you need to burn fat and the media has equated that with enhanced ability to lose body fat.
Hint….that is not necessarily true….but that is a whole other blog post.
Among athletes ketosis has gained popularity as well, but it has nothing to do with the supposed fat loss benefits. When it comes to sports performance carbohydrates are king. While this is true, athletes have taken this to the extreme. It is very common to see athletes at all levels of competition consuming as many carbohydrates as possible all the time. The problem with this approach is that more is not necessarily better when it comes to carbohydrates. The constant intake of carbohydrates causes their body to become dependent on them and they lose their metabolic flexibility and can no longer burn fat.
What is the result of this carbohydrate dependence?
Poor health, mid afternoon crashes, mood swings, and the inability to perform even moderate exercise without carbohydrates.
Some athletes realized that they don’t necessarily need carbohydrates all the time and that they could enter a state of ketosis, upregulating their fat burning and pretty much eliminate the need for constant carbohydrate supplementation.. The problem with ketosis and athletics is that many athletes find their performance suffers due to the lack of carbohydrates.
Luckily science has found a way to synthesize ketones, these ketones are called exogenous ketones, meaning they are produced externally from the body. With this invention it was now possible to provide the body with both glucose and ketones as fuel at the same time.
Could exogenous ketones allow athletes to spare glycogen and keep it around for higher intensity efforts? In theory the body could use the ketones when the intensity is low saving glycogen for higher intensity efforts during a competition.
As you might expect, science is trying to answer this exact question.
In a recent study[1] researchers had 8 endurance trained athletes run for 1 hr at 65% of their VO2 Max to pre-exhaust the athletes and then perform a 10KM time trial. This in theory would simulate competition that had periods of low intensity efforts and high intensity errors, for example at the end of a long race when athletes “drop the hammer” to finish strong. Before the exercise protocol began and after the exercise protocol finished researchers gave participants a cognitive assessment to see how the exercise affected their cognitive performance.
From a dietary standpoint participants consumed 2800 kcal at a macronutrient ratio of 60% carbohydrate, 20% protein, and 20% fat 24 hours before the exercise test. Two hours before the exercise protocol began participants consumed 300-400 calories of porridge and cereal bars consuming about 1g/kg of carbohydrate. Participants were given a drink 30 minutes before exercise, then every 20 minutes during the 1 hour pre-exhaustion session, and then a final drink halfway through the 10km time trial. The drink the participants consumed consisted of either only carbohydrates or carbohydrates and exogenous ketones. Participants were given the ketones at the 20 minute mark of the pre-exhaustion session and at the beginning of the time trial. 
https://pubmed.ncbi.nlm.nih.gov/31730565/
The results of this study showed no significant difference in VO2 Max, heart rate, rating of perceived exertion, respiratory exchange ratio, running economy, lactate levels, glucose levels, time trial performance, and cognitive performance when participants were given carbohydrate only vs carbohydrates plus exogenous ketones. As you might expect, when given the exogenous ketones, ketones levels did rise and peaked at 1.3 MM.
Overall this study showed there were no significant benefits by supplementing with exogenous ketones. This wasn’t the only study that has come to this conclusion, there have been a number of other studies as well[2],[3],[4],[5],[6],[7],[8].
However, there have been other studies that show some potential benefits of exogenous ketone supplementation in athletes.
A study done on team sport athletes showed a lowering of lactate levels when the participants consumed exogenous ketones, however this did not produce improved performance in their shuttle run time. When the athletes did take exogenous ketones they did show improved cognitive performance[9].
Despite most studies on exogenous ketones showed no benefit in athletic performance, there has been one study that did show a 2% increase in bicycle ergometer time trial performance[10].
The benefit of exogenous ketone supplementation is unclear when it comes to sports performance. In theory you would think that it should help in sports that have anaerobic component to it by sparing glucose and lowering lactate levels, but the studies do not seem to back that up 100% of the time.
There are a couple of confounding variables that could affect outcomes. One is how high ketone levels get. It seems athletes might see a greater reduction in lactate levels as well as a greater glucose sparing effect the higher ketone levels get. As with most things though there is going to be an upper limit to the amount of exogenous ketones you can tolerate. Beyond a certain threshold you are likely to experience GI distress.
The benefits of exogenous ketones might also depend on the intensity of the exercise. If the exercise is too easy you might not see any benefit because the exercise is not producing a lot of lactate and not consuming a lot of glucose. You also might not see a benefit at the opposite end of the spectrum either. If the activity is so intense that it is only aerobic, ketones may not even come into play in fueling the activity. The supposed benefit of exogenous ketones comes from its glucose sparing effect and lowering of lactate. If the activity is so easy you are using primarily fat and never need glucose or is so intense that you never use any fat and only use glucose you likely won’t notice a difference.
Finally when it comes to exogenous ketones’ effect on cognitive performance, it might depend on how mentally taxing the cognitive task is. It appears that the more cognitively demanding the task is, the more effect exogenous ketones might play.
The ultimate question is whether you should concern yourself with exogenous ketones if your goal is athletic performance?
Personally, I have never actually used exogenous ketones before. Mostly because I have not seen any clear research that shows their benefits. In theory the sport I participate in, obstacle course racing, would benefit from their supplementation as it is a mixed intensity sport and has aspects of cognitive demanding tasks in it. (I once participated in a race that gave you a random sequence of numbers and letters to memorize in the middle of the race, and then forced you to recall the exact sequence several miles later!)
If someone handed me a free bottle of exogenous ketones to try, I would certainly try it in training to see if I noticed anything. When it comes to the average athlete that I work with though, playing with exogenous ketones falls way down low on the list of priorities. If your diet, sleep, stress, social connection, movement practices, and exercise are a mess then you have no business messing with exogenous ketones and would see far greater benefits by working on those areas first.
In addition, if we look at this idea of having ketones present while also having a significant amount of glucose in the blood, it is a completely unnatural state. Ancestrally this would not be possible, the only way our ancestors could produce ketones naturally would be by depleting glucose. My bias is to avoid ancestral mismatches unless we have proven them to be safe or beneficial otherwise, this is why I focus on lifestyle before supplements.
Bottom line, unless you have everything else dialed in, pass on the exogenous ketones and spend your effort optimizing other lifestyle factors first.
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- (n.d.). No Benefit of Ingestion of a Ketone Monoester … – PubMed. Retrieved October 30, 2020, from https://pubmed.ncbi.nlm.nih.gov/31730565/ ↑
- (2016, August 9). Nutritional Ketosis Alters Fuel Preference and Thereby …. Retrieved October 30, 2020, from https://pubmed.ncbi.nlm.nih.gov/27475046/ ↑
- (2017, July 27). Nutritional ketone salts increase fat oxidation but impair high …. Retrieved October 30, 2020, from https://pubmed.ncbi.nlm.nih.gov/28750585/ ↑
- (2017, October 23). Ketone Diester Ingestion Impairs Time-Trial … – PubMed. Retrieved October 30, 2020, from https://pubmed.ncbi.nlm.nih.gov/29109686/ ↑
- (2018, January 16). Effect of acute ingestion of β-hydroxybutyrate salts on the …. Retrieved October 30, 2020, from https://pubmed.ncbi.nlm.nih.gov/29338584/ ↑
- (2018, February 16). Exogenous ketone salts do not improve cognitive responses …. Retrieved October 30, 2020, from https://pubmed.ncbi.nlm.nih.gov/29451991/ ↑
- (2019, March 29). Nutritional Ketoacidosis During Incremental … – PubMed. Retrieved October 30, 2020, from https://pubmed.ncbi.nlm.nih.gov/30984015/ ↑
- (2020, March 31). Effects of an Exogenous Ketone Supplement on … – PubMed. Retrieved October 30, 2020, from https://pubmed.ncbi.nlm.nih.gov/32269653/ ↑
- (n.d.). Intermittent Running and Cognitive Performance … – PubMed. Retrieved October 30, 2020, from https://pubmed.ncbi.nlm.nih.gov/29944604/ ↑
- (n.d.). Nutritional Ketosis Alters Fuel Preference and Thereby … – Cell Press. Retrieved October 30, 2020, from https://embargoed.www.cell.com/cell-metabolism/fulltext/S1550-4131(16)30355-2 ↑