How Ketones Affect Exercise Performance and Recovery

Exogenous ketones are expensive, and almost all of the high-quality products on the market taste awful. Despite those two downsides, I’ve been using (and recommending) ketone esters like DeltaG for years. So for this article, I wanted to take a deep dive into the scientific evidence on their effectiveness, and compare that research to my hands-on experience using them to bolster my CrossFit performance and recovery. 

Here’s an overview of the key takeaways:

• There’s mixed scientific evidence regarding whether, and to what extent, ketone esters directly improve athletic performance.
• Consuming ketones and protein together improves muscle protein synthesis by activating a key muscle growth pathway (mTOR).
• Consuming ketones before exercise appears to help elite ultra-endurance athletes but may hinder high-intensity activities such as CrossFit and weightlifting.
• Consuming ketones after exercise can reduce inflammation, increase EPO levels, and promote the growth of new blood vessels (angiogenesis) in muscle tissue.
• Ketone supplementation can reduce cognitive decline and improve mental sharpness during intense workouts, thus indirectly contributing to improved performance. 

The bottom line is that leveraging ketones for improving exercise performance and recovery appears to be both an art and a science, so it helps to know what you’re doing. That’s why I encourage you to continue reading to find out how to use these products to your advantage based on your exercise regimen, diet and other factors.

How Exogenous Ketones Work

Ketones are naturally produced by the liver when carbohydrate intake is low, such as during fasting, when following a ketogenic diet, or during prolonged exercise. Exogenous ketones (i.e., ketone supplements) offer many of the benefits of their endogenous counterparts without requiring carbohydrate restriction.

When you consume ketones in the form of ketone salts, ketone esters or butanediol (the three main ketone supplement types), they’re rapidly absorbed into your bloodstream, increasing circulating levels of beta-hydroxybutyrate (BHB) without requiring fat breakdown (which is how the liver produces endogenous ketones). 

The most readily available exogenous ketones are ketone salts, in which BHB is bound to a positively charged ion, such as sodium, magnesium or calcium. While ketone salts are relatively inexpensive to manufacture, they’re less effective than ketone esters (see below) at raising blood BHB levels because esters are more rapidly absorbed and metabolized without the need for additional “processing,” in the form of dissociation and digestion. 

When consumed in excess amounts, the magnesium in ketone salts can also upset the stomach and cause loose stools. However, I should mention that when used in (appropriately) low amounts, the electrolytes found in ketone salts can support athletic performance — particularly if your electrolyte levels are less than optimal due to dietary preferences (i.e., low sodium diets) or low-quality drinking water.

Ketone esters are a more potent form of exogenous ketones, where BHB is bound to a ketone precursor molecule. Unlike ketone salts, ketone esters are absorbed efficiently, leading to a higher and more sustained increase in blood BHB levels. This makes them more effective at mimicking natural ketosis. 

Specifically, ketone esters are broken down to BHB and 1,3-butanediol (BDO) by esterases in the gut. The BHB goes immediately into cells, while the BDO goes to the liver, where it’s turned into BHB and acetoacetate.

Some researchers, like Dr. Dom D’Agostino, claim that BDO can tax the liver. However, I couldn’t find any published papers supporting such claims. To that end, the main downside to unflavored ketone esters is their strong taste (I like to call them rocket fuel).

Check out my best ketones supplements article to learn more about the differences between the various types of exogenous ketones (such as salts, esters and R1,3-butanediol), including my favorite brands.

What’s worth noting is that scientific research exclusively uses ketone esters, not ketone salts. As a result, any time I mention exogenous ketones or ketone supplements in this article, I’m referring to ketone esters.

Ketones Can Boost Endurance, Not Power

Ketones are an aerobic fuel source. That means they require oxygen to be metabolized for energy. When ketones enter cells, they’re converted into acetyl-CoA, which enters the Krebs cycle in the mitochondria. This process generates adenosine triphosphate (ATP), the body’s primary energy currency, but it relies on the presence of oxygen to proceed efficiently.

Because of this, ketones are beneficial for endurance-based, aerobic activities like long-distance running, cycling and steady-state exercise, where oxygen is readily available. However, they do not provide immediate ATP production for high-intensity, anaerobic efforts like all-out sprints or heavy lifting, which rely on glycolysis (the breakdown of glucose without oxygen). This explains why ketones can enhance endurance but are less effective for explosive, short-duration power exercises.

However, it’s crucial to remember that real-world sports — even CrossFit — can include both aerobic and anaerobic elements, so the effect of ketone supplementation can vary by the specific workout or event.

What’s interesting about ketones is that they can generate more ATP per oxygen molecule than glucose. In other words, they improve the energy yield of muscle cells. Additionally, unlike glucose, ketones don’t produce lactate, which can help reduce muscle fatigue and improve overall endurance.

Some studies have also shown that consuming exogenous ketones helps preserve muscle glycogen (aka glycogen sparing), allowing athletes to push longer without “hitting a wall.” A positive side effect of this glycogen sparing is more stable blood sugar levels, which can lead to more consistent endurance performance.

However, it’s worth considering some of the ancillary benefits of ketones, such as improved cognitive function, enhanced mitochondrial function and better sleep, which can indirectly boost athletic performance (even in anaerobic environments) and speed up muscle recovery.

Using Ketones Before Exercise (Performance)

The scientific evidence supporting the use of ketones to improve athletic performance is mixed and heavily context-dependent. That’s particularly true for using ketones as a pre-workout supplement.

Based on the research I’ve reviewed, adequate amounts of ketone esters (in the range of 0.5 to 0.6 grams per kilogram of body weight) are required to improve the performance of elite endurance athletes.

For example, one study involving 39 high-performance cyclists found that consuming 0.573 grams of ketone ester combined with carbohydrates before a 30-minute time trial following a 1-hour ride at 75% max effort allowed the ketone group to ride 2% farther compared to the non-ketone group.

Here’s the thing: supplementing with ketones before a race is not going to turn a hobby cyclist into Tadej Pogačar (who won the Tour De France in 2024). But if you race at an elite level, such as the athletes of team Alpecin-Deceuninck, a 2% improvement in athletic performance can mean the difference between winning and losing.

It’s also worth noting that in some of the studies that showed positive impacts of pre-workout supplementation, athletes consumed both carbohydrates and exogenous ketones. In contrast, no performance improvements were observed when cyclists were given relatively small amounts of ketones (0.35 g/kg) and no carbohydrates.

On the other hand, a study involving male endurance runners concluded that consuming a ketone monoester without co-ingesting carbohydrates did improve the running economy in middle and long-distance runners at submaximal running speeds. (The term “running economy” refers to the energy expended to maintain a certain running speed.)

Taken together, these findings reiterate that researchers don’t yet have a clear picture of exactly if and how pre-workout ketone supplementation impacts performance. 

With that in mind, it’s also worth discussing the cognitive effects of pre-workout ketone supplementation, because those benefits can indirectly impact physical performance. 

Specifically, studies involving ultra-endurance athletes have clearly shown how exogenous ketones can dramatically improve cognitive function and “counteract the decline in psychocognitive functioning during ultra-endurance exercise.” That makes sense, since ketones increase circulating dopamine concentrations, in turn improving mental clarity and alertness.

If you’re a casual fitness enthusiast, you have probably been in a situation where your head calls it quits long before your body. I’d argue that most hobby athletes give up when their perceived exertion reaches a specific limit, which is usually way before they reach their physical limits.

Given everything I’ve learned about ketones over the years, and my personal experience (more on that below), I’d say that exogenous ketones can directly and indirectly help improve athletic performance. If you’re an endurance athlete, consuming adequate amounts of ketones (with or without carbs) before a workout or competition will likely offer a modest performance boost. 

If you’re a high-intensity athlete, I’d consider experimenting with ketones during training sessions to see how you respond. However, based on my research, you might be better off consuming ketones after exercise to improve recovery and sleep while relying on glucose for optimal performance during exercise. 

Using Ketones After Exercise (Recovery)

While the research on exogenous ketones as a pre-workout supplement is mixed, it’s much more robust when leveraging ketones to improve recovery (which can help improve performance over time).

Available research suggests that supplementing with ketones after intense workouts (and before sleep) has anti-inflammatory, anti-catabolic, and pro-angiogenic effects while promoting better sleep, muscle protein synthesis, and increased erythropoietin (EPO) levels to improve oxygen delivery. 

Under normal circumstances, intense physical activity causes an inflammatory response and a breakdown of muscle tissue (catabolic effect). The body tackles most muscle repair and recovery while we sleep (and particularly during deep sleep). Studies have found that supplementing with ketones before bedtime can improve sleep quality, supporting the body’s natural repair and recovery mechanisms.

Additionally, exogenous ketones help curb hunger, lower blood sugar (through glycogen sparing), and improve insulin sensitivity (in healthy individuals). This can help enhance metabolic flexibility (the body’s ability to switch back and forth efficiently between different fuel types), leading to better metabolic health and body composition. Combined, these benefits can further improve athletic performance and recovery over time.

Overall, given the relatively strong scientific evidence, the critical role (endogenous) ketones have played throughout human history (in the temporary absence of food or carbohydrates), I’m convinced that ketones have helped me recover quickly from intense workouts and improve my sleep.

My Experience Using Exogenous Ketones Before and After CrossFit Workouts

I’m not an endurance athlete, and I don’t think humans were born to run, as discussed in episodes 33 and 86 of my Primal Shift podcast. In my early 20s, I was a professional sprinter. But these days (I’m 43 as of this writing), I enjoy CrossFit and lifting heavy weights, and I don’t run on a regular basis.

Everything I’ve said in this article so far might suggest that exogenous ketones are not the ideal fuel source for the type of exercise I enjoy. However, I’ve had only positive experiences with ketones in the context of my CrossFit workouts.

In fact, I’ve performed above average and built lean muscle mass via CrossFit even while following a strict ketogenic diet. These days, I follow an animal-based diet that includes significantly more carbs than are allowed on a keto diet, but I still work out in a fasted state every morning with residual ketones in my bloodstream. 

Once a month, I fast for two days straight and complete two CrossFit workouts during that period. Since abstaining from calories for two days and intensively exercising is draining, I supplement with exogenous ketones. Despite the lack of food and the ketone supplementation before engaging in two CrossFit workouts, I’ve always performed incredibly well.

For example, every year I participate in a grueling CrossFit workout called the Murph Challenge. One year, I completed the challenge at the tail end of a 48-hour fast without using ketones, and it took me 64 minutes. The following year, I did it again with the help of DeltaG Performance, a high-quality ketone monoester used by professional cycling teams. I completed the workout in 54 minutes — a whopping 10 minutes faster than the year before.

For what it’s worth, I remember hitting the proverbial wall much later than usual during that workout, despite not eating anything for 48 hours before the event. 

I realize this is all anecdotal evidence, and no professional athlete in their right mind would compete after not eating for two days. However, this example shows that ketones can help improve performance even in CrossFit.

Of course, several nuances must be considered, including my fuel state, my low fasting insulin levels of 1.8 mmol/L (indicating incredible metabolic flexibility), the specific CrossFit workout (Murph includes running and bodyweight movements, which are, at least, partially fueled by oxygen), and other factors. 

That said, I’ve successfully used exogenous ketones for heavy lifting sessions and high-intensity exercises. In fact, the morning I drafted this article, I crushed a fast-paced sub-six-minute workout (leaving the 20-year-old top athletes in our gym in the dust) after consuming a bottle of DeltaG Tactical. 

I use ketones as a pre-workout supplement (usually together with electrolytes) and consume them throughout the day. I don’t consciously do this to improve physical recovery but to boost my cognitive performance and sleep. As a result, I’ve been getting their recovery benefits without paying extra attention to them.

Side Effects and Limitations

Unflavored ketone esters taste like rocket fuel, and not everyone enjoys that. The good news is that brands like DeltaG offer flavored versions that taste relatively good (even my wife drinks them from time to time). But since I’m not a fan of artificial flavors, I usually stick to the pure esters and appreciate how they proverbially make the hair on my chest grow.

That said, the biggest drawback of using exogenous ketones to improve athletic performance and recovery is our somewhat limited understanding of all the factors that can impact their effectiveness. 

While we wait for more scientific research and clinical trials involving exogenous ketones, I always encourage self-experimentation because the only thing that matters is how ketones work for you.

Final Thoughts: The Research Is Mixed, But I’m Happy With The Results

If you’re a professional endurance athlete, I recommend discussing ketones with your performance coach and experimenting with them during the off-season or practice.

If you’re a power athlete or weightlifter, I’d focus on using ketones to improve post-workout recovery and sleep. If you’re a hobby athlete enjoying various sports (like me), I’d consider using ketones to enhance cognitive performance, recovery and sleep — all of which will likely improve your overall wellness, leading to performance gains over time.

I’ll continue leveraging exogenous ketones to improve my overall wellness, cognitive performance and sleep. If doing so enhances my athletic performance and recovery, I welcome it.

Now, I’d like to hear from you! Have you tried exogenous ketones, and if so, in what capacity? Leave me a comment below, and don’t forget to check out my articles comparing the best ketone supplements. 

Michael Kummer

Michael Kummer is a healthy living enthusiast and CrossFit athlete whose goal is to help people achieve optimal health by bridging the gap between ancestral living and the demands of modern society.