Understanding the Ketogenic State
To understand if you can run on ketones, it’s crucial to know what they are and how your body uses them. Ketones are molecules produced by the liver when the body breaks down fat for energy instead of glucose. This metabolic state, known as ketosis, can be achieved through two primary methods: a very-low-carbohydrate, high-fat (ketogenic) diet or by consuming exogenous ketone supplements.
Endogenous ketosis, triggered by a traditional ketogenic diet, forces the body to become highly efficient at burning fat. Over time, this metabolic adaptation can increase the rate of fat oxidation, meaning athletes can tap into their vast fat stores for energy during prolonged, lower-intensity exercise. However, this adaptation can be a lengthy process and may initially impair high-intensity performance due to the body down-regulating its use of carbohydrates, which are crucial for fast-twitch muscle fibers.
Exogenous ketones, on the other hand, provide a way to raise blood ketone levels rapidly without the dietary restrictions and adaptation period of a keto diet. Athletes can consume these supplements, typically in the form of ketone esters, to access an additional fuel source alongside their usual carbohydrate and fat intake. This approach is often used to promote metabolic flexibility, the ability to efficiently switch between fuel sources based on demand.
Potential Benefits for Endurance Runners
The appeal of running on ketones for endurance athletes is based on several theoretical advantages:
- Glycogen Sparing: Research shows that supplementing with exogenous ketones during exercise can help spare glycogen stores, the body's primary carbohydrate reserves. By using ketones as a supplementary fuel, an athlete can delay the depletion of glycogen, preventing the dreaded "bonk" during long races.
- Increased Fat Oxidation: For long-term fat-adapted athletes, studies have shown a dramatically increased capacity to burn fat for fuel, even at higher intensities. This means their body can rely on a much larger energy reserve than what is available from glycogen alone.
- Enhanced Mental Acuity: Ketones can cross the blood-brain barrier and serve as a super-efficient fuel for the brain. Anecdotal and some emerging research suggest that this can improve focus and mental clarity during the later stages of ultra-endurance events, when mental fatigue often sets in.
- Improved Recovery: Emerging evidence suggests that post-exercise ketone supplementation can accelerate glycogen resynthesis and upregulate cellular signaling pathways involved in muscle repair. This can be particularly beneficial for multi-day events or intense training blocks.
- Reduced Inflammation: Ketones are powerful antioxidants that can help scavenge free radicals produced during exercise, potentially reducing inflammation and aiding overall recovery.
Important Considerations and Drawbacks
While the potential benefits are significant, running on ketones isn't a magic bullet and comes with important considerations:
- Limited High-Intensity Performance: Traditional carbohydrate metabolism is faster for generating energy during high-intensity efforts, like sprinting. For a runner who relies solely on dietary ketosis, performance during these efforts may be impaired.
- Mixed Scientific Evidence: A significant body of research on exogenous ketones still yields mixed results. While some studies show performance improvements in cycling time trials, others find no significant benefit in shorter races for runners.
- Gastrointestinal Distress: The bitter taste and nature of ketone esters can cause stomach upset, nausea, and cramping in some athletes, especially when consumed during strenuous exercise. It is essential to test any ketone supplement extensively during training.
- Adaptation Period (for Dietary Ketosis): Transitioning to a ketogenic diet requires a significant adaptation period, often involving symptoms like fatigue, headaches, and brain fog, commonly known as the "keto flu". This can negatively impact training for several weeks to months.
- Cost: High-quality exogenous ketone supplements, particularly ketone esters, can be expensive, making consistent use cost-prohibitive for many athletes.
Ketogenic Diet vs. Exogenous Ketones for Runners
| Feature | Ketogenic Diet (Endogenous Ketones) | Exogenous Ketones (Supplements) |
|---|---|---|
| Mechanism | Achieves ketosis by severely restricting carbohydrate intake (<50g/day). | Delivers external ketones to the bloodstream, elevating levels quickly. |
| Carb Availability | Extremely low carbohydrate intake. | Can be used alongside a normal or high-carbohydrate diet. |
| High-Intensity Performance | May be impaired due to reduced carbohydrate availability. | Can potentially be used for high-intensity efforts, especially when combined with carbs. |
| Adaptation Period | Long (weeks to months), often involving fatigue and "keto flu". | Immediate effect on blood ketone levels. |
| Recovery | Can help with recovery by lowering inflammation. | Shows promise for enhanced glycogen resynthesis and muscle repair. |
| Cost | Can be cheaper, relying on dietary changes. | Often expensive, especially for ketone esters. |
| Gastrointestinal Issues | Generally low risk once fat-adapted. | Possible GI distress, especially during exercise. |
How to Incorporate Ketones into Your Running
If you're an endurance athlete considering using ketones, a strategic, personalized approach is best. Here’s a general guide:
- Assess Your Goals: Determine if you are an ultra-endurance athlete primarily concerned with steady-state endurance and race-ending mental clarity, or a shorter-distance runner needing high-intensity bursts. The former may benefit from long-term metabolic adaptation, while the latter might find limited benefit and potential downsides from a restrictive keto diet.
- Try Metabolic Flexibility First: Consider a "fuel for the work required" approach. Practice some lower-intensity long runs in a fasted or low-carb state to train your body to burn fat more efficiently. Use carbohydrates for your higher-intensity training sessions.
- Experiment with Exogenous Ketones (in training!): If you are keen to try exogenous ketones, start during a low-stakes training period. Never try a new fueling strategy on race day. A common protocol is to take a dose with carbohydrates before or during long-duration endurance efforts. You may also experiment with a dose post-workout to potentially aid recovery.
- Listen to Your Body: Pay close attention to how you feel. Track your energy levels, perceived effort, and performance. Use a blood ketone monitor to track your actual ketone levels and see how your body responds to different fueling strategies.
- Consider Professional Guidance: Work with a registered dietitian or sports nutritionist who specializes in endurance sports to help you develop a personalized fueling plan. This is especially important for dietary ketosis, as it involves significant changes to your macronutrient intake.
Conclusion
Yes, you can run on ketones, but it's a nuanced topic with different implications depending on the method used. A fat-adapted state from a ketogenic diet can provide a vast and steady energy source for very long, lower-intensity endurance efforts, while exogenous ketone supplements can offer a third fuel source for athletes seeking to spare glycogen and enhance recovery. However, neither is a substitute for consistent training, and both require careful experimentation to understand how your body responds. For most runners, a strategy focusing on metabolic flexibility—using both fat and carbohydrates effectively—will offer the most performance benefits.
How It Works: The Fourth Fuel Source
While carbohydrates and fats are the primary fuels, the body also uses ketones. This is particularly relevant for endurance athletes in long events where glucose stores are limited. When your body is in ketosis, the brain can use ketones for up to 60% of its energy needs, preserving blood glucose for muscles. This metabolic shift is what gives ketones their edge, offering an alternative energy pathway that can prevent mental and physical bonking.
Additional Benefit: Mitochondrial Efficiency
Research has explored how burning ketones might improve the efficiency of mitochondrial oxidative phosphorylation, meaning your muscles could potentially do more work with less oxygen. This would provide a significant advantage in endurance events.
Ketones and Lactate
Ketone drinks have been shown to decrease lactate levels during exercise, which is traditionally associated with a lower rate of carbohydrate oxidation. While some interpret this as carbohydrate impairment, others suggest it allows for more controlled fuel use, extending endurance.
Here is a link to the scientific review article referenced in some of the source material.
Limitations and Further Research
The science on performance benefits is still evolving, with studies showing mixed results depending on the type, duration, and intensity of exercise, as well as the type of ketone supplement used. Individual responses can vary significantly, so personal experimentation during training is key. Researchers are continuing to explore the best protocols and use cases for runners.
