Ketogenic Diet & Trail Running: Performance or Illusion?

Ketogenic Diet & Trail Running: Performance Tool or Metabolic Dead End?

The ketogenic diet frequently comes up in discussions among trail runners, especially for ultras: less refueling, fewer digestive issues, “unlimited” energy. Before adopting such a radical dietary strategy, one question deserves to be asked: what does exercise physiology actually say?

Here, we analyze the scientific data on the ketogenic diet, endurance, and trail performance, far from fleeting trends and marketing hype.

3 Key Ideas About the Ketogenic Diet in Trail Running

1. Burning More Fat Doesn't Guarantee Better Performance

Scientific data clearly converges: the ketogenic diet significantly increases fat oxidation during exercise.

However, this metabolic adaptation does not translate into performance gains:

• VO₂max remains stable
• Speed does not increase
• Running economy sometimes deteriorates

Changing fuel alters the engine but often reduces its efficiency.

2. The More Intensity Varies, The More Restrictive Keto Becomes

At low intensity, performance generally remains similar. As soon as the effort approaches the threshold — climbs, surges, changes in pace — the situation changes:

• Energy cost increases
• Oxygen consumption rises
• Heart rate climbs
• Perceived effort becomes higher

In trail running, where intensity fluctuates constantly, this loss of efficiency becomes structural.

3. The Ketogenic Diet Influences Training Adaptations

Some studies show that the ketogenic diet can:

• Limit the development of mitochondrial function
• Reduce carbohydrate utilization during exercise
• Attenuate certain training-induced adaptations

Training remains demanding, but the body progresses less efficiently.

Scientific Insight: What the Literature Shows

Published systematic reviews and meta-analyses present a consistent picture:

• ✅ Lipid oxidation significantly increased
• ❌ No improvement in VO₂max, speed, or time to exhaustion
• ❌ Higher energy cost at moderate to high intensity
• ❌ Running economy sometimes degraded
• ⚠️ Potentially limited mitochondrial adaptations

The ketogenic diet optimizes one fuel at the expense of the engine's versatility.

Scientific References

• Bailey, C.P., Hennessy, E. A review of the ketogenic diet for endurance athletes
• Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers
• The effect of a ketogenic low-carbohydrate, high-fat diet on aerobic capacity and exercise performance in endurance athletes: A systematic review and meta-analysis
• Effect of high-fat or high-carbohydrate diets on endurance exercise: a meta-analysis
• High-fat feeding inhibits exercise-induced increase in mitochondrial respiratory flux in skeletal muscle

Practical Advice for Trail Runners

🔹 For performance: prioritize a balanced or carbohydrate-rich diet, adapted to your training load.

🔹 For ultras: train your digestive system, rather than eliminating carbohydrates.

🔹 For health: be wary of extreme strategies, especially during intensive blocks.

🔹 For sustainable endurance: metabolic flexibility beats rigid specialization.

Key Takeaways

• ✔️ The ketogenic diet does not boost trail running performance
• ✔️ It improves fat oxidation but degrades running economy
• ✔️ In hilly terrain and varying intensity, it is disadvantageous
• ✔️ The most effective diet is one that supports training

— Antoine, Baptiste, and Etienne from TRL