• Does Nutritional Ketone Supplementation Improve Athletic Performance?

    I have written about the advantages of changing to a higher fat diet and how many athletes, including myself, have been able to reduce supplemental nutrition during racing. This supplemental nutrition has been in the form of carbohydrate drinks, chewable gels, commercial bars and homemade foods.

    More recently, people have begun to question whether or not using supplemental/dietary ketones (sometimes referred to as exogenous ketones) is an advantage for athletes.

    I was able to find one study in Cell Metabolism that examined nutritional ketone supplementation. The study was interesting in that researchers designed five studies within one umbrella study. Depending on what you like, you can get:

    • the quick and dirty (read Summary, Want to Experiment?)
    • a tad more detail (read Summary, Questions/Concerns, My Opinion and Want to Experiment?)
    • all the gory details (read Summary, Studies 1 through 5, Questions/Concerns, My Opinion and Want to Experiment?)

     The Summary

    The research branch of the US Army, Defense Advanced Research Projects Agency (DARPRA), put out a $10 million call for the development of the most efficient food for soldiers to take onto the battlefield. A group of 18 researchers across various departments at the University of Oxford, the University of Cambridge, UK Sport and the Laboratory of Metabolic Control in the USA were among those answering the call. Their study results are summarized in this column.

    Ketones are produced naturally by the body in states of fasting, starvation, very low calorie intake, low carbohydrate diets and certain exercise situations. Ketones are made in the liver by mobilized body fat. In the situations described in the first sentence of this paragraph, internal fat stores are broken down to make ketones which can then be utilized by nearly every part of the body. Every person has enormous stores of fat, an advantage of ketones vs the body utilizing glycogen for energy. Glycogen stores are very limited.

    The study looked at how the body utilized dietary supplemental ketones, without controlling daily diet to force the body to naturally produce ketones. For example, individuals could have been consuming a very high carbohydrate diet, not producing any ketones naturally, and be part of this study. With that in mind, it appears that:

    • Supplemental ketones inhibit glycolysis, therefore conserving glycogen as well as producing less lactic acid.
    • Nutritional ketones may increase metabolic flexibility during exercise.
    • Those consuming a ketone plus carbohydrate (dextrose) drink were able to cycle further in a 30-minute time trial.

    (If you don’t like a lot of detail, skip to the Questions/Concerns and Recommendations sections.)

    Study 1

    Six male athletes consumed an equal amount of dietary ketones1 (573 mg/kg of body weight) in a drink at rest and during a 45-minute exercise session that consisted of cycling intensities at 40% and 75% of maximum wattage (WMax). The study was a randomized crossover design, meaning the same subjects received a ketone drink on one visit and a carbohydrate drink on the other visit. They did not know which drink was served on the respective test dates.

    The results indicated that the ketone drink increased ketone oxidation during exercise from roughly 0.35 g/minute to 0.5 g/minute at 40% and 75% WMax, respectively.

    Bottom line: Consuming ketones increases the body’s ketone usage during exercise, without any dietary controls. In other words, athletes did not have to be on a keto-adapted diet for the body to utilize ketones.  

    Study 2

    Ten male athletes did a three-way crossover study looking at a fixed cycling intensity of 75% WMax. The three drinks were taste-matched and included calorie-matched beverages containing dextrose (CHO), Ketones (KE) and fat (FAT). I cannot tell the composition of the FAT beverage other than the study noted it as “long-chain fat.”  

    Fifteen minutes prior to the start of exercise, test subjects ingested 573 mg/kg of body weight of KE, isocaloric FAT or CHO.  After consumption of the drinks and prior to exercise, intramuscular concentrations of ketone bodies were about three-fold higher after consuming KE, than after the ingestion of FAT or CHO. After exercise, intramuscular ketone concentrations after consuming KE remained double the concentrations compared to consumption of FAT or CHO.

    Results of this study included that blood lactate concentrations were the same at baseline conditions and then changed during exercise to significantly lower on the KE drink than the CHO and FAT drinks. Exercise caused increases in plasma glycerol following both CHO and FAT, but not after KE. Also glycolytic intermediates were significantly lower after KE versus CHO and FAT. The sum of glycolytic intermediates decreased in proportion with increased intramuscular ketones.

    Bottom line: Researchers concluded the findings suggest that ketosis suppressed muscle glycolysis – the supplemental ketones spared muscle glycogen.

    Study 3

    Eight male athletes were involved in a randomized, single-blind, cross-over study that included a drink where KE and CHO were combined in a single drink. They completed three time trials of one hour at 75% WMax. One ride drink was KE+CHO, a second was CHO and a third was nicotinic acid, or vitamin B3. The B3 was a control drink.

    After drink consumption and at rest, muscle biopsies revealed that ketone concentrations were seven-fold higher in the KE+CHO than CHO or B3. Ketones remained high for KE+CHO at five-fold greater than CHO or B3. Also, intramuscular hexose concentrations were significantly higher on KE+CHO vs CHO or B3, reflecting a preservation of intramuscular carbohydrate stores. Blood lactate concentrations were negatively correlated with hexose concentrations. That is, the higher the hexose concentration, the lower the lactate measure.

    Bottom line: The synergistic combination of KE and CHO appears to increase ketone usage, preserve CHO stores and reduce lactate.

    Study 4

    Seven male athletes completed a two-way crossover study by riding for two hours at 70% VO2Max intensity. They consumed an isocaloric, taste-matched drink that was a combination of 60% CHO (dextrose) and 40% ketones (KE+CHO) or 100% CHO. This study examined intramuscular stores of FAT and glycogen.

    The plasma metabolites were reproducible between study participants and comparable with Studies 1 through 3. There was a regular ingestion of drinks during exercise, at a rate I could not find in the document. Plasma glucose concentrations were roughly 1-2mM higher on the CHO drink.

    This study noted that blood lactate concentrations were significantly decreased for the KE+CHO, compared to CHO only. Respiratory exchange ratios were lower for the KE+CHO drink, suggesting more fat oxidation. No differences were found for insulin or cortisol levels between the two drinks.

    Bottom line: On the KE+CHO drink, lower levels of lactate were produced compared to a CHO drink.

    Study 5

    Six male and two female (finally!) athletes did two time trials consisting of a one-hour steady state workload at 75% VO2Max, followed by a 30-minute time trial for maximum distance. The drinks were KE+CHO or CHO alone. Athletes were blinded to work output, heart rate and cadence. Only elapsed time was visible.

    Similar to Studies 3 and 4, blood lactate concentrations were lower on KE+CHO than CHO. Blood glucose were lower on KE+CHO during the first 25 minutes, but were similar by the one-hour mark. When athletes consumed the KE+CHO drink they cycled an average of 411 meters (+/- 162 meters) longer than when consuming CHO alone.

    Bottom line: On the KE+CHO drink there appear to be lower levels of lactate produced and improved performance.


    Though I am quite interested in the study results and it does show some promise for utilizing ketones for athletic performance, I do have a few questions or concerns:

    • This is only one study, I would like to see more studies replicating parts of the design.
    • Each single study had relatively small sample sizes, 10 or fewer individuals.
    • There were only two women in the entire study of 39 individuals.
    • All test subjects were high-level athletes.
    • It would have been better to include a KE-only drink in Study 3, 4 and 5 to compare KE vs KE+CHO.
    • For athletes that are already on a low-carbohydrate diet and producing their own ketones, do supplemental ketones reduce body-initiated fat burning?
    • For athletes that are already on a low-carbohydrate diet and producing their own ketones, does supplementing with CHO-only during exercise produce the same results as high carbohydrate diet athletes using KE+CHO?
    • Is there any limit to supplementing with ketones or does the body just waste excess?

    My opinion

    This is an extremely interesting area of research. I think that, perhaps, those athletes that naturally produce ketones by adhering to a low-carb diet and supplementing with CHO in races can (are?) doing the same thing as the study result. That is, low-carb athletes naturally produce ketones by burning their own fat, supplement with carbs in races, have metabolic flexibility, reduce lactate and extend endurance. I've always thought that doing a Fat-Burning Machine diet (modified for athletes) allows endurance athletes' bodies to switch back and forth between ketones and glycogen. That opinion, of course, needs to be proven.

    On a personal level, "all of the benefits and none of the pain" never flies with me. To go ahead and eat a high-carb diet and then just supplement with ketones to get benefits the "same as a low-carb diet," I don't buy it. Even if we're talking exercise-only situation.

    Want to experiment?

    The drink mix in the study won’t be commercially available for a year. I don’t know how the current keto drinks compare to those used in the study. If you want to experiment with the currently-available drinks, it appears that there is low risk of problems. Just don’t be gulping the stuff morning, noon and night.

    How will you know if the keto drink helps you or not? Do multiple experiments on your own and compare power, speed and HR data.

    I suspect that supplementation rate (calories) for a KE+CHO drink will be somewhere around 150 to 300 per hour for those following a traditional high-carb diet. I think those doing a Fat-Burning Machine type diet can consume fewer calories, as is currently normal. Based on the athletes reporting back to me, a typical range is 50 to 150 calories per hour. Keep yourself on the low end for anything between 1 and 3 hours.

    Stay tuned

    Count on me to keep an eye out for new information. Stay tuned here.


    1. Dietary ketones were an edible form of ketone made by transesterifying ethyl (R)-3-hydroxybutyrate with (R)-1,3-butanediol using lipase. Researchers have shown that the nutritional ingestion of this (R)-3-hydroxybutyl (R)-3-hydroxybutyrate ketone ester (KE) is a safe and effective way of elevating blood ketone levels and provides a means of investigating human ketone metabolism independent of caloric or CHO deficit.


    Cox, P.J., et al, “Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes. Cell Metabolism, 24, 256-268, August 9, 2016, Elsevier Inc.


    Be sure to see if I have an easy-to-use training plan for you on my site to help you reach your goals. And, there are more options on the TrainingPeaks site.

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