Ketones, Endurance Cycling, and the Truth Behind the Hype

I cleaned this into a smoother, more publish-ready article, kept your message and tone, and added image placement ideas throughout. I also verified the key science/current cycling context: the UCI’s 2025 position says it does not recommend ketone supplements because there is no compelling evidence they improve performance or recovery; a 2024 road-cycling review describes the evidence as theoretically interesting but inconsistent; and the ISSN’s 2024 position stand notes ketogenic diets are generally neutral or detrimental for athletic performance compared with higher-carbohydrate diets, despite increasing fat oxidation. (UCI)

Ketones have become one of the trendiest topics in endurance sport. They are talked about like a secret weapon: a cleaner fuel, a way to spare glycogen, a way to ride longer, recover faster, burn more fat, think more clearly, and somehow unlock another layer of performance without changing much else. And, of course, now we have small, expensive bottles of liquid ketones being marketed directly to cyclists, ultra-endurance athletes, and anyone chasing the next edge. But when we step away from the marketing and look at the physiology, the story becomes much more complicated.

Ketones are real. Ketones are interesting. Ketones are part of human metabolism. But liquid ketone supplements are not magic, and for most endurance cyclists, they are not the performance breakthrough they are often made out to be. To understand why, we first need to understand what ketones actually are.

Ketones are molecules produced by the liver when carbohydrate availability is low and fat metabolism increases. This can happen during fasting, prolonged exercise, very low-carbohydrate diets, or starvation. The three main ketone bodies are beta-hydroxybutyrate, acetoacetate, and acetone. Beta-hydroxybutyrate, often written as BHB, is the one most often discussed in performance and supplementation. In a natural state, ketones are a backup and support fuel system. When glucose availability is low, the body starts relying more heavily on fat, and the liver converts some of that fat-derived energy into ketones. Those ketones can then be used by the brain, heart, and muscles as fuel.

That is actually a brilliant survival mechanism. It helps humans function when food is scarce, when fasting, or when carbohydrate intake is very low. But here is the important part for cyclists: ketones are not the body’s preferred high-intensity cycling fuel. For endurance cyclists, especially those doing tempo, sweet spot, threshold, VO2 max, climbs, attacks, gravel surges, or racing, carbohydrate is still king for higher power output. Carbohydrate can produce ATP quickly, and that matters when the effort rises. Fat and ketones can contribute to energy production, but they do not replace the need for glycogen and glucose when intensity increases.

This is where the ketone conversation gets messy. A lot of marketing takes a true piece of physiology — that ketones can be used as fuel — and stretches it into a much bigger claim: that taking ketones will automatically improve endurance performance. That is where the evidence becomes much weaker.

There is also a big difference between endogenous ketones and exogenous ketones. Endogenous ketones are ketones your body makes on its own. This happens when carbohydrate intake is low, glycogen is reduced, or you are in a ketogenic state. Exogenous ketones are ketones you consume from outside the body, usually in the form of ketone salts, ketone esters, or newer liquid ketone products.

That distinction matters because taking ketones does not mean your body is in the same metabolic state as someone who has adapted to ketosis. You can drink ketones, raise blood ketone levels, and still have full glycogen stores, normal insulin responses, and carbohydrate metabolism happening at the same time. In other words, liquid ketones can create “ketosis on paper,” but they do not automatically recreate all the adaptations that happen with fasting or a ketogenic diet.

This is one reason the supplement is so marketable. It promises the benefits of ketosis without the work of actually being ketogenic. You can eat carbohydrates, train hard, and still drink ketones. That sounds perfect for cyclists because no one wants to give up carbs and lose top-end performance. But the real question is not whether ketone drinks raise ketone levels. They do. The real question is whether that improves performance, recovery, or health in a meaningful way.

So far, the evidence is not nearly as exciting as the marketing. Some early studies suggested ketone esters might improve endurance performance, which helped create the hype. But later research has been far more mixed, and several reviews have found limited or inconsistent benefits. A 2024 review focused on road cycling concluded that while ketones are theoretically interesting, field studies have shown disappointing performance effects, with individual responses varying and long-term data still lacking. That matters because cycling is not performed in a lab-perfect bubble. Cyclists deal with terrain changes, heat, gut tolerance, fueling demands, intensity surges, hydration, race stress, and fatigue. A supplement that looks interesting mechanistically does not always translate into real-world performance.

The International Society of Sports Nutrition’s 2024 position stand on ketogenic diets also reported that ketogenic diets tend to have neutral or detrimental effects on athletic performance compared with higher-carbohydrate diets, even though they increase fat oxidation. That point matters because it reminds us that burning more fat does not automatically mean performing better. Endurance performance is not just about what fuel you burn. It is about how fast you can produce energy, how much power you can sustain, how well you recover, and whether you can repeat efforts when the ride gets hard.

This is one of the biggest mistakes in endurance nutrition conversations. Athletes hear “more fat burning” and assume that means better endurance. But cycling performance is not just about using fat. It is about metabolic flexibility. You need the ability to use fat at lower intensities, but you also need carbohydrate availability when power goes up. A cyclist who becomes excellent at burning fat but loses the ability to produce high power has not gained performance. They have traded one ability for another.

Liquid ketones often get marketed as a way to “spare glycogen.” In theory, if the body uses ketones as an additional fuel, it might preserve carbohydrate stores. That sounds appealing for long rides and ultra-endurance events. But in practice, the body does not always behave that simply. When ketones are elevated, they can sometimes suppress carbohydrate oxidation, which might sound good during easy endurance work but could become a problem when intensity rises and the body needs rapid carbohydrate energy.

For a cyclist, glycogen sparing is only useful if it does not come at the cost of power output. If ketones make you feel slightly different but reduce your ability to surge, climb, attack, or sustain race pace, that is not a win. The goal is not to burn the most exotic fuel. The goal is to ride well.

Another major issue is GI tolerance. Many ketone products are hard on the stomach. Ketone esters in particular are known for having a very strong taste and may cause nausea, bloating, reflux, or general gut discomfort. Ketone salts may be easier for some athletes, but they often come with a mineral load, and they may not raise ketone levels as much as esters. For cyclists, this is not a small detail. The gut is already under stress during endurance exercise. Blood flow shifts away from digestion and toward working muscles, the heart, lungs, and skin. Add heat, dehydration, carbohydrate mix, caffeine, sodium, gels, and race nerves, and the gut is already doing a lot. Adding liquid ketones on top of that can become one more stressor, especially if the athlete has not practiced with them.

And this is where I think the conversation needs to become more honest. Most cyclists do not need a more complicated supplement stack. They need to fuel enough carbohydrate. They need to hydrate better. They need to practice gut training. They need to recover. They need enough total energy. They need sleep. They need consistent training. They need to stop chasing marginal gains before mastering the basics.

Ketones are often marketed to athletes who are already under-fueled, over-stressed, and looking for a shortcut. That is where the hype becomes a problem. A cyclist who is not eating enough carbohydrate during long rides does not need liquid ketones. They probably need more carbohydrate. A cyclist who is constantly bonking does not need a ketone shot. They need a better fueling plan. A cyclist who cannot recover from intervals does not need to “hack metabolism.” They need enough calories, protein, carbs, hydration, and rest.

That does not mean ketones have no possible use. The science is still evolving. There may be specific situations where exogenous ketones have a role, especially around recovery, cognitive fatigue, ultra-endurance, or clinical contexts. Some researchers are still exploring whether ketone esters could influence glycogen resynthesis, appetite, inflammation, sleep, or brain function after very demanding exercise. But the key word is “could.” The evidence is not strong enough to justify the sweeping claims often made in marketing.

In fact, cycling’s governing body, the UCI, issued a 2025 recommendation against the use of ketone supplements in professional cycling, not because they are banned, but because it saw no compelling evidence that they improve performance or recovery. Ketone supplements remain legal, but the UCI stated that it does not recommend including them in riders’ nutrition plans. That is a big statement in cycling because ketones have been so visible in the pro peloton. For years, they were surrounded by mystery, rumor, and performance speculation. Riders were seen using them. Teams experimented with them. Brands marketed them aggressively. But visibility does not equal proof.

Just because a supplement appears in elite sport does not mean it is the reason elite athletes are elite. Pro cyclists also have world-class genetics, years of training, carefully controlled nutrition, team chefs, massage, recovery protocols, altitude camps, lactate testing, and enormous support systems. If they use ketones, that does not mean ketones are the missing piece for everyone else.

For most cyclists, especially amateur, gravel, masters, and ultra-endurance athletes, the return on investment is questionable. Liquid ketones are expensive. They can taste unpleasant. They can upset the stomach. Their performance benefits are inconsistent. And they may distract athletes from the fundamentals that actually move the needle.

The more interesting conversation is not, “Are ketones good or bad?” The better question is, “What problem are you trying to solve?” If the problem is bonking, ketones are probably not the answer. Better carbohydrate intake is. If the problem is gut distress, ketones may make it worse, not better. If the problem is poor recovery, look first at total energy intake, carbohydrate restoration, protein, hydration, sleep, and training load. If the problem is low energy during long rides, look at breakfast, hourly fueling, sodium, hydration, and pacing. If the problem is wanting to burn more fat, remember that low-intensity endurance training already improves fat oxidation without needing an expensive bottle. If the problem is cognitive fatigue in an ultra, ketones might be interesting in theory, but they should be tested carefully in training and never treated as a replacement for calories, carbs, caffeine strategy, sleep management, or pacing.

This is where nuance matters. Ketones are not fake. They are real molecules with real metabolic roles. But liquid ketones are often sold with more confidence than the science supports. The body is not a simple machine where adding a new fuel automatically improves output. Metabolism is a network. When one fuel changes, other pathways shift too. Glucose, glycogen, fat oxidation, lactate metabolism, insulin, stress hormones, hydration, gut absorption, and mitochondrial energy production all interact. Cyclists do not perform better simply because more ketones are floating in the blood. They perform better when the right fuel is available at the right intensity, the gut can absorb it, the muscles can use it, and the brain can stay regulated under stress.

This is why carbohydrates remain so important. During moderate to high-intensity cycling, carbohydrate is still the most effective fuel for producing energy quickly. This does not make fat or ketones useless. It simply means they have a different role. Fat supports long-duration lower-intensity work. Ketones may serve as an alternative or supplemental fuel in certain low-carbohydrate states. But when the ride demands power, acceleration, climbing, or repeated hard efforts, glucose and glycogen matter.

The hype around liquid ketones often comes from the desire to bypass the hard parts of endurance sport. Athletes want more energy without more food. More fat burning without sacrificing power. Better recovery without eating enough. More mental clarity without sleeping. More performance without doing the boring basics. But endurance does not work that way. The body adapts to consistent training, adequate fueling, smart recovery, and repeated exposure to the demands of the sport. Supplements can sometimes help, but they cannot replace the foundation.

If a cyclist is curious about ketones, I would not frame them as forbidden. I would frame them as experimental. Do not use them for the first time on race day. Do not use them instead of carbohydrates. Do not assume they will prevent bonking. Do not assume that because they raise blood ketones, they improve performance. Test them during training, pay attention to the gut, track power and perceived exertion, and ask whether they actually solve a problem. Most of the time, the answer may be no. And that is okay.

Not every shiny supplement needs to become part of your routine. The best endurance athletes are not the ones with the most complicated fueling plan. They are the ones who understand what their body needs, when it needs it, and how to support the work being asked of it.

Ketones are fascinating from a science perspective. They show us how adaptable the human body is. They remind us that metabolism has backup systems, alternate fuels, and survival pathways. But for cyclists chasing performance, the current evidence does not support liquid ketones as a magic endurance fuel. The real edge is still much less glamorous: eat enough, fuel early, use carbohydrates strategically, train the gut, hydrate well, recover hard, and build metabolic flexibility through training, not shortcuts.

And remember, the goal is not to have the trendiest fuel in your bloodstream. The goal is to ride strong, think clearly, recover well, and keep showing up.