This article was written by Kevin Sprouse, DO, CAQSM. Dr. Sprouse is a team physician for the Cannondale Pro Cycling Team, has a degree in exercise science, and is board-certified in two medical specialties. He practices Sports Medicine at Provision Sports Medicine in Knoxville, TN.
The relationship between diet and performance is well established. Most athletes are aware that the energy needed to perform and recover can be obtained through the consumption of a combination of carbohydrates, fats, and proteins (collectively referred to as “macronutrients”). By altering the ratios of macronutrient intake, an athlete can tailor their diet for various performance goals. The specific ratios are up for debate, but the principal remains.
There is another dietary source of energy which has only recently been recognized as a potential contributor to athletic performance. No...I’m not talking about alcohol, although if you’ve not read my last article about The Beer Mile, you should! Ketones, or more accurately “ketone bodies”, are a hot topic in sports nutrition. We’ll delve into the science and a little self-experimentation in this post.
To understand this, we’ll first take a brief look at the basic science. For those of you who are not scientifically-inclined, this will not be terribly dense material. For those who are a bit nerdier, like me, realize that this is a glossy overview. The simplicity might offend some, but the idea is to make this concept digestible for a large audience. If you want to dig deeper, there are some very technical resources that you can reference. That, however, is not the scope of this article.
Most athletes understand that the body functions on a mixture of fuels. The harder the effort, the more glycogen (stored carbohydrate) your muscles will burn. Conversely, less intense efforts rely more on the oxidation of fat. Your muscles are not the only energy-hungry organs in your body though. The brain actually requires a significant amount of ATP (think of this as the “currency” of energy). In most cases, the brain will utilize primarily glucose, or sugar, to function. When the glucose runs out, the brain stops working. Since we can only store about a day’s worth of brain fuel in our liver, this can be an evolutionarily tenuous situation. (We store more glycogen in muscles, but that is not available for use in the brain.) In order to allow our species to live longer than a day when food is scarce, our bodies have developed the ability to create ketone bodies from fat and utilize them as brain fuel. This process allows us to live as long as 30-40 days without food.
There are potentially other benefits in having ketones floating around in your bloodstream, a state known as “ketosis”. Some evidence suggests that ketosis allows for greater energy expenditure at rest, which is what many would think of as a “higher metabolism”. This is far from a physiologic certainty, but it might be helpful for weight loss. More research is needed to answer this question. Likewise, there is the possibility that ketosis leads to improved performance. If such a benefit is proven, it will likely apply only to certain parameters of performance, such as aerobic capacity and muscular endurance. In other words, ketosis is unlikely to improve your 100m sprint time, but it might be useful for that 40km time trial.
Your body is producing ketone bodies at all times, but you are not always in ketosis. It’s generally accepted that these potential performance benefits occur with a ketosis of 1.5mM - 2.5mM. (That is a measure of ketone body concentration in the blood.) Attaining this level of ketosis by simply restricting carbohydrate intake is both difficult and unlikely to lead to improved performance. And this is where exogenous ketone consumption comes into the picture! (Exogenous alludes to the fact that they are synthetic and/or ingested rather than produced within the body.)
There are generally two types of exogenous ketones. One is a ketone salt and the other is a ketone ester. These are two different molecular structures. Ketone salts are more commonly available and generally consist of Beta-hydroxybutyrate (B-OHB) bound to sodium. The problem with ketone salts is, well, the salt. In order to ingest enough B-OHB to reach ketosis, you end up taking in a massive load of salt. This can lead to gastrointestinal problems and a dehydrating effect. Ketone esters tend to be more effective at inducing ketosis and avoid the salt intake, but there are no commercially-available ketone esters yet. This is likely due to the fact that they taste heinous which leads to a difficulty in marketing.
Most of the academic work on the use of exogenous ketones in athletes has been performed by Drs. Kieran Clark and Pete Cox at Oxford University. Unfortunately, they have yet to publish the data they’ve gathered, despite rumors of some very interesting findings. In their work on the topic, they have developed a proprietary ketone ester which has been used by the British Olympic program and a few professional endurance athletes with some success. This product has been promised commercially as “Delta G” energy drink, but it has not yet come to market. (For you science buffs, “Delta G” is a reference to the thermodynamic principle of Gibb’s Free Energy.)
So, what does all of this boil down to? Exogenous ketone ingestion and the resulting “acute nutritional ketosis” is unlikely to be a performance panacea. If it was, WADA would righfully ban it! However, this is potentially one more tool in your nutritional arsenal. Obtaining a ketosis of 1.5-2.5mM prior to a TT-type effort may impart a slight performance benefit, but it almost certainly will act like a “nutritional safety net” against suboptimal fueling. In other words, if you’ve not nailed your nutrition regimen, exogenous ketones can help to spare glycogen usage and delay the dreaded “bonk”. This is how the pros have been using ketones, but this assumes that you have access to a ketone ester.
Since ketone esters are not readily available yet, I set out to experiment with some commercially available ketone salts. To do this, I purchased a blood ketone monitor (available on Amazon), a glucometer (or blood sugar monitor, also available on Amazon), and was fortunate enough to have the nice folks at a ketone supplement company send me some product to use. Briefly, here’s what I found:
- Ketone salts are salty...really. This product had 970mg of sodium, and it tasted like it. That’s a lot of sodium to pour down the hatch, especially if you’re not someone who generally eats a lot of salt. I started by taking a half-dose for the first few days, which did seem to help me acclimate to the load.
- My general diet consists of a decent amount of healthy fats. I also periodize my carbohydrate intake, matching it to the athletic task at hand. With this in mind, I generally started the day with a waking ketone concentration of about 0.5mM and a blood glucose of 75-80 mg/dL. That was before ingesting any exogenous ketones. From that level, I still found it hard to reach a ketosis greater than 1.0mM when taking a full dose of B-OHB salts. And I don’t think I could stomach any more than a full dose.
- I did not enjoy the taste of the ketones, but they weren’t as bad as the ketone esters (which have been described to me as drinking diesel fuel mixed with vinegar). They also tended to make me a little nauseated, which I understand varies from individual to individual. It was never so bad that the ketones came back up though.
- During this experiment, I completed a few runs and bike rides with a ketone concentration of 1.0 - 1.2 mM at the outset. During these, I maintained an extended, subthreshold effort with occasional intervals of higher intensity. I never ingested any other macronutrient during the workout and had generally fasted for 10-12 hours beforehand. I consumed only water and the occasional amino acid supplement. While I have no objective measure, I did feel like I had consistent energy and often felt better after 75-90 minutes than I did when first starting. Perhaps that is placebo, but it was a reliable effect.
Ultimately, it seems to me that the consumption of an exogenous ketone ester (not salt) will become a nutritional strategy used to gain that extra 1% and buffer the effects of a suboptimal fueling strategy. It is rare that even the most disciplined athlete plans and executes their nutrition strategy perfectly, so having a backup is nice. If someone is eventually able to bring such a product to market, I would not be surprised to see it used rather commonly...assuming it is palatable. In the meantime, I think it will remain the purview of national olympic programs and professional teams.