How much would you pay to run your next race 2 percent faster? If you can run a 5K in 30 minutes, that’s a 36-second improvement; in the context of a 4-hour marathon, you would save almost 5 minutes.
That 2 percent improvement is the claimed potential of a new “superfuel” called ketone esters. Is this new product the next big advance in sports nutrition or destined to join the long list of forgotten would-be game changers? (Believe it or not, alcohol was once used as an “energy drink” for runners.) Here’s a look at what you need to know.
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What Are Ketones?
Because they’ve been a hot topic recently, you’ve probably heard of ketones: molecules your body produces from breaking down fat for fuel when you’re starving or otherwise carbohydrate-deprived. Hence, the ketogenic diet, which has become popular in the last few years, involves eating very few (or almost no) carbs in order to promote fat burning, which produces ketones.
While many people today look for elevated ketone levels to confirm that they are in a state of ketosis and burning fat (and hopefully losing weight), the diet has also been shown to suppress appetite, improve mental focus, and even treat mood disorders. (The diet was developed in the 1920s to treat epileptic children.) Whether the ketones themselves play a role in these effects remains to be seen; it might be other elements of the overall diet that make the difference, which is why there’s still a lot of research being done on the topic.
Unlike natural ketones produced by a ketogenic diet, ketone esters are exogenous—meaning they are made outside your body—and produced by mixing ketones with an alcohol compound to make them drinkable. Exogenous ketones themselves aren’t new; they’ve been administered during metabolism/hormone research through needles for decades. What makes ketone esters noteworthy is that they are ingestible, so they are considerably more practical than the intravenous kind. Yet they raise ketones to the same level as a ketogenic diet would, all without eliminating carbs or risking other unhealthy side effects (like raising sodium off the charts, the way ketone-salt drinks do).
Rocket Fuel?
The possibility of a 2 percent performance benefit stems from research conducted by the University of Oxford, University of Cambridge, UK Sport, and the National Institutes of Health, published in Cell Metabolism in 2016. In the study, eight elite cyclists cycled moderately for an hour and then performed a 30-minute time trial. On average, they improved their performance by 2 percent, riding about one quarter-mile farther when they consumed a ketone ester drink (about two shots’ worth) before the first hour of cycling compared to a calorically equivalent placebo.
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Brendan Egan, an associate professor of Sport and Exercise Physiology at Dublin City University, and his colleagues are currently following up this research with a study that mimics the protocol in runners. Preliminary findings point to similar results; however, Egan cautions against assuming ketone esters will work as a performance enhancer for everyone, all the time. “We think that ketones will be beneficial to performance in certain contexts, but not all contexts.”
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Specifically, he points out that the shorter the event and the greater the intensity, the less useful ketones will be. Egan just demonstrated that ketone ester did not benefit high-intensity intermittent running performance in a protocol that simulated a soccer game. The reason is that the harder you push your body, the quicker it needs energy. Your body is always burning a mix of fuel (glucose, fat, ketones if they’re available); that mix depends on a variety of factors, including gender and what you have (or haven’t) eaten. At a certain intensity your body will want to burn primarily carbs, because that’s its quickest source of energy.
Think of your body as a hybrid car, which is designed to optimize available fuel sources to give you the best mileage. At lower intensities, your body can rely more on fat (or ketones), which is slower to access but plentiful in supply. As you pick up the pace, you’ll start relying more heavily on carbs; when you race a 10K, you’re fueled almost entirely by carbs.
Additionally, “evidence is strong that people who are most likely to benefit from ketone use are the most fit,” Egan says. Animal studies have shown that wheel and treadmill running increase the number of enzymes needed to break down ketones for energy, as well as the number of “transporter” proteins necessary to shuttle ketone fuel into hungry muscles. Furthermore, because these ketone-specific enzymes and transporter proteins are most active in slow-twitch muscle fibers, it is hypothesized that people with higher proportions of slow-twitch fibers—i.e., more “natural” endurance athletes—will be able to use ketones better than folks who don’t exercise.
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The “Third Fuel Tank”
Again, your body primarily operates on two fuel tanks: carbohydrates (which you’ll burn more of during tempo runs and interval workouts) and fat (which you’ll burn more of during a long easy run). While your body can store only about 1,500 to 2,000 calories of carbohydrates (4 calories per gram), fat storage capacity is almost unlimited, making it ideal for endurance events like marathons.
Yet, relying too much on fat has downsides. Burning fat requires more oxygen than burning carbs, which is why when you “hit the wall” (i.e., run out of carbs), you have to slow down. You can become more efficient at burning fat while you run, by either eating low-carb diets like Keto, Atkins, Whole30, or Paleo, or running long distances at a target pace to teach your body to burn a higher percentage of fat at that effort (thereby sparing your glycogen, i.e., stored carbs). These fat-burning adaptations can take weeks, months, or even years.
That’s where ketone esters may help, by operating as a “third tank.”
“Ketone ester allows you to have a normal diet and have high ketones,” says Geoffrey Woo, CEO and cofounder of HVMN (pronounced “human”), a company that sells the first commercially available ketone ester drink, HVMN Ketone, which costs $99 for three 2.2-ounce bottles. By consuming exogenous ketones, athletes give themselves an additional source of fuel that they can burn first, thus preserving glycogen. (That is, of course, if they can get past the taste. I liken the flavor to a mixture of raspberry-flavored vodka, cough syrup, and nail polish remover, others have described it as a mix of rubbing alcohol and toilet cleaner with a hint of fruit.)
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By providing a non-carb fuel source, ketone esters also reduce the amount of lactate your body produces—because, as Woo says, “ketones burn cleanly” and do not convert into lactate at all, the way carbs do. With less lactate, your muscles feel less tired. As a result, ketone esters may contribute to lower perceived exertion and a feeling of steadier energy throughout a run.
Recovery Elixir?
In addition to enhancing performance, there is evidence suggesting that ketones promote better recovery. In a review article published in the Journal of Physiology last year, Egan and colleagues evaluated the existing research on how ketones affect the body during and after training.
They concluded that post-exercise ketosis, whether achieved through diet or supplementation, is likely to help with both rebuilding glycogen and resynthesizing muscle—the two main goals of recovery. In post-exercise ketosis, the body burns ketones for energy, thus “sparing” carbohydrates (needed for glycogen) and protein (needed for muscle). However, in order to access this ketone-driven benefit, runners trying to induce ketosis through diet would need to avoid eating carbs—which is typically what they should eat immediately after a workout during the time window when the body can store glycogen away the fastest.
Ketone esters appear to solve this problem.
“The suggestion,” Egan and his coauthors write in their review, “is that the co-ingestion of exogenous ketones and carbohydrates in a recovery protocol can confer a metabolic advantage.” By consuming ketone esters along with the usual amounts of carbs and protein recommended post-workout, runners can reap dual benefits.
Unanswered Questions
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Despite the buzz, research and theory behind ketone esters still leave many questions unanswered. Do they dampen the body’s ability to burn glucose—which would affect a runner’s ability to surge or put in a high-intensity burst? Can they help recreational athletes, or are benefits limited to elites?
Thus far, the only scientific studies that have found a performance benefit in humans have been conducted on the latter—people at the very top of the performance spectrum. And on small sample sizes (just eight cyclists in the study mentioned above), which isn't an accurate representation of the total population. Still, the anecdotal evidence is enough to at least spark interest.
“During the run, I feel like you have a real solid energy that’s sustained energy,” says Jeff Browning, a.k.a. Bronco Billy, an ultrarunner and online endurance coach. He experimented with ketone esters leading up to Western States, the world’s oldest 100-mile trail race, and placed fifth in the race in June. “The ketone esters worked great,” he says of the in-race experience. “I used three bottles total. Felt ‘on’ the entire time. No major lows in energy. Definitely worked.”
My long-run trial with HVMN Ketone was similar: My energy level was extremely consistent, and I never felt hungry, despite having skipped breakfast.
The Bottom Line
Initial research and early anecdotal evidence seem promising for ketone esters. That said, the research is still in its infancy. And the most important aspect of using a ketone supplement is its effect on blood ketone levels, which need to be monitored. Both Browning and my trials are based on subjective feedback, not objective data, and it’s possible that placebo effect can account for some of the perceived benefits. But for me personally, if I could run a whole marathon feeling as energized as I did during that long run? Well, let’s just say I spend more than $99 on shoes alone.
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