Running and the Ketogenic Diet

Running is one of the most widespread aerobic activities, practiced for general well-being, weight loss, and athletic performance. In recent years, more and more runners are experimenting with the ketogenic diet (keto) as a nutritional approach to improve body composition and optimize fat metabolism.

But is running really compatible with a low-carb, high-fat diet? Let's analyze the running + keto combination from a technical yet accessible perspective.

What is the ketogenic diet?

The ketogenic diet is based on a drastic reduction in carbohydrates (< 50g per day), a moderate protein intake, and a high fat intake. This setup induces a physiological state called nutritional ketosis, where the body uses fats and ketone bodies as its primary energy source.

Running and energy metabolism: an overview

During running, the body primarily uses muscle glycogen and fatty acids as fuel. At low intensity, fat oxidation prevails; at medium-high intensity, glycogen becomes crucial. Keto fits into this context by modifying the balance between the two substrates.

Metabolic adaptation: the transition phase

When transitioning from a high-carbohydrate diet to a keto diet, the body enters an adaptation phase that lasts 2–6 weeks. During this phase:

• Glycogen levels drastically decrease.
• Performance may temporarily decline, especially during high-intensity workouts.
• The body learns to efficiently oxidize fats and produce ketone bodies.

Low vs. high intensity performance

Low intensity (e.g., slow long runs, aerobic running)

• Excellent context for keto.
• The body primarily burns fats, even in the absence of carbohydrates.

High intensity (e.g., intervals, sprints, short races)

• Performance may suffer.
• Glycogen remains the most efficient source for explosiveness.

Recovery and adaptation

One of the limitations of pure keto is the lower availability of glycogen for muscle recovery. Glycogen promotes post-workout protein synthesis and adaptation to training stimuli. Including a small amount of post-run carbohydrates (e.g., 20–30g of starches or low GI fruit) can: speed up recovery, reduce chronic fatigue, and not compromise ketosis if carefully calibrated.

Hydration and electrolytes

In a ketogenic state, there is a physiological reduction in insulin levels, leading to increased diuresis and loss of electrolytes (sodium, potassium, magnesium). It is essential to:

• Drink more than usual, even 2.5–3 L/day
• Supplement salt (2-3g per day) and foods rich in potassium and magnesium (e.g., avocado, nuts, bicarbonate-alkaline water)
• Use specific electrolytes during long runs (> 60 minutes)

Every runner is different: metabolic individuality

The response to keto varies based on: body composition, type of training, age and gender, insulin sensitivity, and metabolic state. Some runners transform into fat-burning machines. Others experience performance drops, cramps, or slow recovery.

Conclusion

The ketogenic diet can be a valuable ally for runners, especially for medium to long distances and with the goal of optimizing lipid metabolism, reducing inflammation, and improving body composition. But it is essential to: understand when to use it, personalize it, maintain a good intake of micronutrients, water, and electrolytes, and potentially integrate it with targeted carbohydrates at specific times.

Recommended approach: long-distance running, trail running, slow long runs = great with keto. Intervals, sprints, fast races = better with a modulated low-carb approach. Goal: run long, well, and with stable energy.