This one really puts the icing on the cake… err, well since this is keto, the butter on the bacon?
Regardless, in today’s article we’re going to be winding down the keto craze with recent research providing some concrete and convincing evidence contrary to the ketone supplement company claims.
If you’ve been following along recently in the RADLAB, and want to make sense of all this keto diet and exogenous ketone talk, then you need to read this article...
New Ketone Study
A recent article that came out this year is one of the first articles that looks at the ingestion of ketone salts as a supplement and its effects on exercise performance compared to a placebo.
In this particular study, recreationally active participants were studied either fasted or after the ingestion of 300 mg/kg body weight of ketone salts. What makes this study interesting is that exercise in the fasted state is already a disadvantage state since it’s well-accepted that carbohydrate supplements can improve performance. Therefore, this study can evaluate the effectiveness of ketone salts without the comparison to any other known ergogenic aid to see if it has any benefit at all.
The recruitment of non-trained participants, and the use of commercially available ketone salts in this study makes the conclusions a little more relatable relative to previous investigations despite the dose of ketones remaining extremely high. A dose of 300 mg/kg of body weight still represents between 24-29 g of ketone salts per dose for the average male.
Two major outcomes were observed in this study. The effect of exogenous ketones on exercise performance, and the effect on fuel selection.
The results of this study indicated that it took participants on average 46 seconds longer to complete a 10 km cycling time-trial in the ketone condition, representing a significant 7% decrease in performance. Furthermore, the average power output during the time trial was 6.3% lower, which the authors declare as a large decrement in performance from consuming the ketone salts.
For the first time, we have fairly conclusive evidence that not only are ketone salts an inferior energy source than a carbohydrate supplement, but ketone salts are actually inferior for exercise performance and power output compared to supplementing with nothing at all, in a fasted state.
I have previously discussed how ketosis is not advantageous during high-intensity, short duration anaerobic activities such as sprints. Now with this latest study we can add moderate-intensity, moderate duration activities such as a 10 km time trials to that list.
To reiterate my previous thoughts about ketones and performance, they really do not serve a beneficial purpose either on their own or in conjunction with a keto diet. The keto diet may be your desired mechanism to lose fat, but the sacrifice will inevitably be exercise performance and power output, not just for anaerobic activities but moderate-intensity exercise as well. In fact, the ingestion of ketones will only make matters worse as exercise performance appears to be superior in a fasted state compared to supplementing with ketone salts.
The second objective of the study was to analyze what substrate was being oxidized during the exercise protocol. However, the interpretation can be quite misleading.
In this portion of the study, participants engaged in 15 minutes of cycling at progressive intensities. The results of this study indicate that the ketone ingestion (300 mg/kg body weight) caused a significant decrease in RER during low-intensity exercise compared to a placebo control.
On the surface, this appears to imply that fat metabolism increased, however, when you dig through the details, the consumption of over 20 grams of ketone led to a net decrease in total calories burned and only a net increase of about 0.07 grams of fat burned. As uninspiring as that already is, there is no current method to distinguish ketone oxidation from fatty acid oxidation, so it’s likely that the extremely small increase in fat oxidation was actually the ketones themselves, or worse, the ketones taking over most of the energy expenditure and none of it coming from endogenous fat stores.
Unfortunately, the calculation used to determine substrate oxidation rates were not disclosed in this publication, but the reference they use in the methods do not take ketone oxidation into consideration.
Evidence of fat oxidation during ketone ingestion is severely lacking. It has been established that ketones do not improve fat oxidation at rest, nor at high-intensity exercise. However, there appears to be some ambiguity if ketone ingestion has any effect in fat oxidation during low-intensity exercise. If anything, extremely high amount of ketones can influence intramuscular fat content during low-intensity exercise, but current research has failed to observe any influence in systemic fat oxidation rates.
As research progresses on this topic, if a measurable benefit is discovered, there are still at least two limitations to its practicality; the dosage required to achieve the effect, and the size of the effect. The dose of ketones in these studies are impractically large for commercially available ketone supplements, and the effect sizes are so small that even if statistically significant, they may not make a noticeable difference to make it worthwhile.
Bottom Line on Ketones in Research
The key takeaway from the scientific literature is simply that there is no established practical benefit for ketone supplementation at all to date.
What we know from research is that carbohydrates certainly provide performance benefits in all exercise intensities, whereas ketones have been shown to be detrimental to performance. Therefore, if your goal is to maximize exercise performance, neither a ketogenic diet, nor exogenous ketone salts will be beneficial or advantageous for you.
Finally, since there is no superior fat loss outcome obtained through a ketogenic diet compared to an equal calorie, high carb diet, it would appear that the use of a keto diet is more of a personal preference for those who have trouble voluntarily reducing calories and sticking to a strict regimented diet. Therefore, if you are only interested in losing body fat and not concerned about any decrements in performance, then keto can be considered an equivalent alternative to strict dieting, or possibly for adding some variety in dieting strategies.
Hopefully this three-part series of articles has helped clear up the confusion around all things keto. If you have any further questions or comments regarding the topic, feel free to message us on social media or email us at firstname.lastname@example.org and I’ll be happy to respond.
- Jeukendrup AE, Wallis GA. Measurement of Substrate Oxidation During Exercise by Means of Gas Exchange Measurements. Int J Sports Med 26; S25-S37, 2005.
- O’Malley T, Myette-Cote E, Durrer C, LIttle JP. Nutritional ketone salts increase fat oxidation but impair high-intensity exercise performance in healthy adult males. Appl Physiol Nutr Metab. 42; 1031-1335, 2017.