Will ketones actually improve your performance?

I’m sure you’ve seen exogenous ketones being marketed as the next big ergogenic aid during ad breaks on your favourite endurance sports podcasts. But what does science say about ketones’ effectiveness when it comes to improving your performance?

Let's break down what happens when you take ketones before, during and after exercise, so you can decide whether you should be using them…

What are ketones?

Your body has two main sources of fuel it can burn for energy: carbohydrates (stored as glycogen in your muscles and liver, or ingested through food and sports nutrition) and fat, with carbs the main source of fuel used during endurance exercise at moderate-to-high intensities. 

So, where do ketones fit in? Your liver makes ketones by breaking down fat, which your muscles and brain can then burn directly for energy. But, your body only produces significant amounts of ketones when carbohydrates are scarce - like during prolonged fasting or on a strict low-carb diet. 

The idea behind ketone supplements is simple: what if you could drink ketones directly, and give your body an extra fuel source without having to deplete your carb stores first? That's potentially very interesting for an endurance athlete, since running low on glycogen is a key reason we hit the wall. But not all forms of ketones are the same … 

Before we explore the performance benefits, let’s define the three main types:

1. Ketone monoesters  like DeltaG are the strongest form. Drink one, and your blood ketone levels rise quickly into a range similar to what you'd see after days of fasting - without any dietary restriction. 
2. Ketone precursors  like Ketone-IQ work indirectly - your body has to convert them into ketones first. This makes them slower-acting and less powerful than monoesters.
3. Ketone salts  are an older class of compounds that bind ketones to sodium or potassium. They're the weakest option in terms of raising blood ketone levels. Taking enough to make a difference often means consuming a lot of sodium at the same time.

In practical terms, a single 25g serving of a ketone monoester raises blood ketones roughly 3–4 times higher than even a large dose of a ketone precursor - and keeps them elevated for longer. 

For the rest of this article, we'll focus on ketone monoesters, since that's where the strongest research and the most potential applications lie…

Will drinking ketone ester improve performance?

When evaluating supplements like ketones, it's useful to separate physiological, psychological and performance outcomes. A supplement that changes your blood chemistry (physiological) doesn't necessarily make you feel better (psychological), and even if it does tick both the physiological and psychological boxes, it might not make you faster (performance). 

So, can you have a shot of ketones before or during a race and expect to go faster? The short answer: probably not.

The initial excitement in this space was sparked by Cox et al. (2016), who reported that well-trained cyclists went ~2% further during a 30-minute time trial (following 60 minutes at a fixed relative intensity) when a ketone ester was combined with carbohydrate. However, subsequent studies from KU Leuven, using longer and more race-realistic protocols, have not replicated that benefit.

In a 2020 study by the KU Leuven team, 12 highly trained male cyclists completed a simulated cycling race consisting of 3 hours of intermittent cycling followed by a 15-minute time trial and an all-out sprint. They received 65g of ketone monoester (in three boluses of 25g, 20g and 20g) alongside 60g of carbohydrate per hour, or a control drink with the same carbohydrate intake.

There was no benefit to performance in terms of mean power output in the time trial, nor time to exhaustion in the sprint.

Crucially, the study also tested the main proposed mechanism by which ketones could help with glycogen sparing. The idea is that if your muscles can burn ketones to power your legs instead of carbohydrates, you could spare glycogen for when you really need it at the end of a race. The data didn't support this. Net muscle glycogen breakdown was actually higher with ketones.

What did happen was a significant drop in blood pH and blood bicarbonate with ketone ingestion. In other words, the ketones made the blood more acidic. So, by the time you reach the hard end of a race, where buffering capacity matters most, you've spent some of your acid-base reserves metabolising the ketones. An acidic state is considered to negatively impact high-intensity efforts, which is why some pro cyclists consume sodium bicarbonate ahead of decisive climbs.

Could sodium bicarbonate and ketones together benefit performance?

The KU Leuven group didn't stop there. Having identified the acid-base problem, they asked: what if we co-ingest sodium bicarbonate to counteract the ketoacidosis?

In a follow-up study with nine well-trained cyclists completing the same race simulation, they tested four conditions: ketone monoester alone (65g), bicarbonate alone (300 mg/kg body weight), ketone ester plus bicarbonate, and a control - all with 60g carbohydrate per hour.

The combination of ketones and bicarbonate was the only condition that improved performance versus any other condition. Mean power output during the 15-minute time trial was ~5% higher with ketones and bicarbonate.

This is a genuinely interesting finding. But there's a critical nuance: the performance benefit appeared at the end of a 3-hour race, at a time when blood ketone levels had fallen back toward baseline. 

So, was it really the ketones driving performance, or was the bicarbonate doing the heavy lifting?

Ketones during high intensity exercise

To test how any performance effects may depend on the exercise intensity directly, the same group ran another study - this time with 14 well-trained cyclists completing a 30-minute time trial (without the preceding 3-hour ride) followed by an all-out sprint. 

Mean power output during the time trial was 1.5% lower with both ketone conditions, compared to control and bicarbonate alone. Bicarbonate co-ingestion was not sufficient to counteract this negative effect.

This is an important finding. When ketone levels are genuinely elevated during high-intensity exercise, performance is impaired. And adding bicarbonate didn't fix the problem.

The sprint was a different story: bicarbonate alone improved time to exhaustion by ~8% regardless of whether ketones were present.

Do ketones interfere with carbohydrate fueling?

A key question that earlier ketone studies couldn’t answer was whether ketones interact with the high carbohydrate intakes athletes actually use on race day. Most prior work used modest carb doses (60g/h or less), well below the 75-90g/h (and beyond) that endurance athletes are increasingly targeting. 

In 2026, Martyn et al. tested what happens when you combine a ketone monoester with a race-realistic carbohydrate intake of 120g/h in eight well-trained cyclists. They measured exogenous carbohydrate oxidation during 3 hours of cycling at 95% lactate threshold, followed by a ride to exhaustion.

Co-ingesting ketone monoester with 120g/h of carbohydrate reduced the rate of exogenous carbohydrate oxidation from 1.50 to 1.35g/min. This meant that roughly 9g/h less carbohydrate was burned from the drinks consumed.

Based on this, and the prior finding of increased utilisation of muscle glycogen with ketone use, it appears they may actively interfere with your body’s ability to use the carbohydrate you’re consuming. 

Considering we spend considerable effort optimising gut training and carbohydrate delivery, adding a supplement that reduces the effectiveness of that fueling strategy is counterproductive. 

As Shaw et al. (2020) concluded in their comprehensive review in Sports Medicine: "in contrast to contemporary, high(er)-carbohydrate fueling strategies, inducing nutritional ketosis is rarely ergogenic irrespective of origin and, in fact, can impair endurance performance."

Can ketones aid recovery?

If the acute performance story is underwhelming, the recovery and adaptation story is far more compelling.

The landmark study by Poffe et al. (2019) gave 25g of ketone ester after each training session during a brutal three-week overload training block (two sessions per day, six days per week). The ketone group also received a second dose before sleep (total of 50g per day for three weeks).

The results were striking:

•    Sustainable training load in week 3 was 15% higher in the ketone group than the control group

•    Power output in the final 30 minutes of a standardised 2-hour endurance test was 15% higher in the ketone group

•    The ketone group showed blunted increases in nocturnal adrenaline and noradrenaline, markers of sympathetic overactivation that characterise high levels of stress and poor training tolerance

•    Resting heart rate decreased by 6 beats per minute in the control group but increased by 2 bpm in the ketone group: the control group was showing classic signs of overreaching, while the ketone group wasn't

In essence, the ketone group was able to tolerate significantly more training stress. The athletes weren't just recovering better; they were adapting better.

What about normal training blocks?

In 2026, Robberechts, Poffe et al., conducted a study where 28 trained males completed eight weeks of supervised cycling while receiving either 25g of ketone monoester or a placebo after each session and again a second dose before sleep.

The headline finding: 30-minute time trial performance was 4% higher in the ketone group at the end of the training period. The results suggest enhanced oxygen uptake by the muscles. Furthermore, post-exercise ketone supplementation appeared to amplify the mitochondrial adaptations to training. More and more efficient mitochondria, better oxygen utilisation in the muscles, and improved performance.

Key takeaways

Let's bring this together with a clear summary of what the science tells us:

Ketones taken during exercise (acute use):

•    Do not improve endurance performance

•    Do not spare muscle glycogen

•    Causes a significant drop in blood pH and bicarbonate, reducing your buffering capacity

•    May slightly impair high-intensity performance

•    Co-ingestion with sodium bicarbonate may unlock a benefit at the end of prolonged events, but the bicarbonate itself may be undoing the negative effects of ketones at high intensity

•    Reduce exogenous carbohydrate oxidation and oxidation efficiency, undermining your race-day fuelling strategy

Ketones taken after exercise (chronic/recovery use):

•    May blunt symptoms of overreaching during heavy training blocks

•    Maintain appetite and energy balance during demanding training periods

•    Amplify mitochondrial and vascular adaptations to endurance training

•    Improve endurance performance over weeks of supplementation (+4% in 30-minute time trial)

•    These effects appear to be driven by enhanced peripheral (not cardiac) adaptations

There’s little to suggest that ketone ester supplementation before or during exercise will enhance your performance. If you're in a phase of heavy training and you're looking for an edge in recovery and adaptation, post-exercise ketone supplementation is promising. The KU group's body of work provides evidence that ketones taken after exercise can help you tolerate more training stress and may even better adapt to it.

Whether the performance gains justify the cost is a personal decision that depends on your budget, your training phase, and how hard you're pushing.

Ultimately, exogenous ketones are not a substitute for getting the fundamentals right: adequate carbohydrate intake during exercise, personalised hydration with appropriate sodium replacement, and sensible caffeine use. Those remain the pillars of race-day performance nutrition.

We'll continue to monitor the research closely and update our position as more data becomes available.

Further reading

• How much carbohydrate do athletes need per hour?
• How to measure your sweat rate
• Should athletes use caffeine?
• How to avoid overtraining and burnout