Understanding Ketones as a 'Fourth Fuel'
To understand what do ketones do for running, you must first grasp their basic function. Ketones, or ketone bodies, are energy molecules produced by the liver when glucose is in short supply. They are derived from the breakdown of fatty acids and can be used as an alternative fuel source by the brain and muscles, particularly during states of low carbohydrate availability, such as prolonged exercise or fasting. They are often referred to as the body's 'fourth fuel tank,' alongside carbohydrates, fats, and protein.
Runners can elevate their blood ketone levels in two main ways: through a very low-carbohydrate ketogenic diet or via exogenous ketone supplements. While the ketogenic diet forces the body into a state of ketosis by restricting carbohydrates, exogenous supplements provide ketones directly, allowing athletes to potentially utilize them without altering their entire macronutrient intake.
The Theory: How Ketones Were Supposed to Help
Before a wave of conflicting research, the theory behind using ketones for running was compelling. Proponents argued that ketones could:
- Spare Glycogen: By providing an alternative fuel source, ketones could reduce the body's reliance on its limited carbohydrate (glycogen) stores, saving them for critical high-intensity moments.
- Boost Performance: Some early studies suggested marginal endurance improvements, leading to hope that ketones could act as a potent ergogenic aid.
- Enhance Mental Acuity: Ketones can cross the blood-brain barrier, leading to theories that they could improve focus and cognitive function during long, fatiguing runs.
- Reduce Lactate: Some research indicated that ketones could lead to lower blood lactate levels during exercise, potentially delaying muscle fatigue.
The Reality: Mixed Results for Performance and Recovery
Despite the promising theories, the actual research on ketones' impact on running performance has yielded largely inconsistent results. While a 2016 study on elite cyclists showed a performance gain with ketone esters, multiple subsequent studies on runners attempting shorter distances like 5K and 10K have found no benefit. Worryingly, some research has even suggested that exogenous ketone use could impair performance, especially during high-intensity efforts, possibly due to changes in metabolism or blood pH.
The Stronger Case for Recovery
Where the evidence for ketones becomes more convincing is in the realm of recovery. Several studies suggest that ketones may be more beneficial when consumed post-exercise rather than pre-race.
Here’s how they may aid recovery:
- Accelerated Glycogen Resynthesis: When ingested with carbohydrates after a workout, ketones might help speed up the replenishment of muscle glycogen.
- Reduced Overreaching: A study on trained athletes undergoing an intensive training block found that those supplementing with ketones showed fewer signs of overreaching, suggesting better resilience and adaptation to high training loads.
- Improved Sleep: Anecdotal reports and some preliminary sleep studies suggest that ketones can improve sleep quality, which is vital for recovery.
The Importance of Context
The effect of ketones is not a simple equation. The outcome depends heavily on the specific context, including the type of supplement, the timing, the duration and intensity of the exercise, and the individual athlete's physiology.
| Feature | Exogenous Ketone Supplements | Traditional Carbohydrate Fueling |
|---|---|---|
| Primary Fuel Source | Provides an alternative fuel source (ketones) to supplement carbs. | Provides glucose (from sugars and starches) as the primary fuel. |
| Effect on Performance | Mixed and often inconclusive, potentially negative for high-intensity efforts. | Proven, reliable source of energy for all exercise intensities. |
| Impact on Glycogen | Proposed glycogen-sparing effect; research is inconsistent. | Directly replenishes and sustains glycogen stores. |
| Recovery Potential | Potential for enhanced recovery, particularly post-exercise with carbs. | Standard and effective method for muscle glycogen resynthesis. |
| Potential Side Effects | High risk of gastrointestinal issues (nausea, cramping) and poor taste. | Generally well-tolerated, with some potential for stomach issues with specific formulations. |
| Cost | Very expensive. | Cost-effective and widely available (e.g., gels, chews, sports drinks). |
Drawbacks and Considerations for Runners
Before considering ketone supplements, runners should be aware of several significant downsides:
- Taste and GI Issues: Many runners report the taste of ketone esters to be overwhelmingly bitter and unpleasant, with a high risk of stomach discomfort, nausea, and cramping, which can seriously derail a training run or race.
- Cost: Ketone supplements are very expensive, with a single serving costing as much as a new pair of running shoes over a typical training block. For most runners, investing this money in proven strategies like better nutrition, coaching, or gear would yield far greater returns.
- Limited Research: Scientific understanding of ketones' effects on runners is still in its early stages. There is limited data on long-term safety and how they affect different populations, including female athletes, who process fat differently.
- Not a Replacement for Carbs: Combining ketones with carbohydrates is critical. Using them alone can actually impair performance by suppressing the body's use of carbs for high-intensity power.
Conclusion: A Supplement for the Edgy, Not the Everyday Runner
For the vast majority of runners, what ketones do for running is not enough to justify the high cost and potential for gastrointestinal distress. The evidence for direct performance gains is unconvincing, and proven, more affordable supplements like caffeine, creatine, and carbohydrates offer far more reliable benefits. While post-exercise ketones show some promise for accelerating recovery, they should be considered a marginal gain for elite or high-volume athletes, not a replacement for fundamental nutritional principles. For most amateur runners, a focus on smart training and a balanced, carb-rich fueling strategy will deliver the most significant and consistent improvements. For a deeper dive into the metabolic aspects of performance, a review published in the Journal of Physiology provides an excellent overview on the topic.
