Should You Be Slurping Olive Oil Like Kilian Jornet?

Last week, Kilian Jornet posted a photo of himself filling a soft flask with olive oil. Not Maurten. Not Tailwind. Not flat Coke. Extra virgin olive oil, ready to sip on his States of Elevation adventure.

Imagine pulling into an aid station and watching someone top off their bottle with the same thing you use to season a cast-iron skillet. It is equal parts horrifying and impressive. If anyone can get away with it, it is Kilian. We can marvel at his gastrointestinal fortitude without implementing his strategy wholesale.

Olive Oil as Endurance Fuel: A Brief and Greasy History

This is not entirely new. Olive oil has a long, slippery history in sport. The ancient Greeks swore by it, consuming it for energy and rubbing it on their bodies before competition. For them, it was essentially the original energy gel: calorie-dense, portable, and available in bulk if you did not mind carrying a clay amphora to the stadium.

From a purely nutritional standpoint, the logic is not insane. Olive oil is pure fat, around 120 calories per tablespoon, which means it delivers a significant amount of energy in a very small volume. For long, sustained, aerobic efforts in the mountains, caloric density matters. Weight matters. And if your body can actually access and use fat efficiently as a fuel source at the intensities you are working at, a flask of olive oil starts to look less ridiculous than it did thirty seconds ago.

Why It Might Actually Work for Kilian

For Jornet's specific context: long, steady days moving through the mountains at intensities that rarely spike into zones demanding rapid carbohydrate oxidation, high-fat fueling has a plausible physiological rationale.

After decades of high-volume aerobic training, elite ultra-endurance athletes develop a significantly enhanced capacity to oxidize fat at intensities that would force recreational athletes to rely heavily on carbohydrate. Research on highly trained endurance athletes consistently shows fat oxidation rates and intensity ceilings that are meaningfully higher than in recreational or moderately trained populations. Kilian is, to put it mildly, at the far end of that distribution. Add likely genetic advantages in metabolic flexibility, and a flask of olive oil becomes less of a stunt and more of a rational fueling choice for his specific goals and physiology.

He has also written extensively about metabolic efficiency and fat oxidation as a training priority. If you have read Training for the Uphill Athlete, you know that he and his co-authors place significant emphasis on building the capacity to burn fat at higher intensities as a foundation for mountain performance. That is a coherent and well-reasoned strategy for the kind of projects he does.

Why It Will Probably Wreck You

Before you start decanting Costco EVOO into your soft flasks, let's talk about what fat fueling actually does to most people during exercise.

Fat digestion is slow under the best conditions. During hard exercise, your body is actively shunting blood away from the digestive system toward working muscles, which makes fat digestion even slower and less efficient. A tablespoon of olive oil is significantly more likely to sit in your stomach like a greasy brick than to power you up a climb. The window between "this is fine" and "I need to find a bush immediately" is narrower than you think and highly individual.

Olive oil also contains zero carbohydrate. That matters because carbohydrate is the primary fuel for higher-intensity efforts, the fuel your brain preferentially uses, and the substrate required to replenish glycogen. If you need to surge, respond to terrain changes, compete, or simply climb a hill without your legs turning to concrete, carbohydrate availability is not optional. Fat oxidation, however well-trained, cannot fully substitute for carbohydrate at moderate to high intensities. The research on carbohydrate restriction as a strategy for improving fat oxidation is genuinely mixed, and the performance costs at anything above easy aerobic pace are real and consistent.

You can build a better aerobic base and improve fat oxidation capacity through training. You cannot eat your way to Kilian's metabolic profile by swapping gels for olive oil. Those adaptations come from years of structured aerobic work, not from the contents of your flask.

The N of One Problem

The more interesting question the olive oil flask raises is not whether fat is a valid fuel source. It is about how we consume and interpret information about elite athlete fueling choices.

Kilian was not trying to influence anyone. He was documenting his own project, making choices that make sense for his physiology, his goals, and his specific context. Social media did the rest. The storyline became "famous runner does weird thing" and the implication, even if unstated, is that the weird thing might be worth trying.

This is the survivorship bias problem in athletic fueling, and it shows up constantly. We see what elite athletes do. We do not see the decades of training that produced the physiology that makes those choices viable. We do not see the failed experiments, the GI disasters, the strategies that got quietly abandoned. We see the flask of olive oil and wonder if we are missing something.

Kilian's olive oil is fascinating precisely because it is an n of one experiment. It tells us something interesting about the outer edge of human metabolic adaptation. It does not tell us anything generalizable about what most runners should put in their flasks.

What This Means for Your Fueling

The takeaway here is not that Kilian is wrong. The takeaway is that Kilian is Kilian and you are you.

For the overwhelming majority of endurance athletes doing events with any intensity variation, variable terrain, competitive elements, or efforts lasting under 24 hours, the evidence base for fueling still points in the same direction it always has. Carbohydrates are the primary performance fuel. Electrolytes support fluid balance and muscle function. Adequate total caloric intake matters for sustained efforts. These are not exciting conclusions. They are, however, the ones supported by the research.

Fat oxidation capacity is worth developing through aerobic base training. It is one tool in a well-developed metabolic toolkit. It is not a replacement for carbohydrate at the intensities most runners are working at, and high-fat fueling strategies during races introduce GI risk that the evidence does not justify for most people.

Olive oil belongs on focaccia. Unless your goal is a DNF with the words "extra virgin" glistening on your singlet.

We dig into fueling myths, elite athlete survivorship bias, and what the evidence actually supports for active people on Your Diet Sucks. If you want more of this with people who are also tired of reverse-engineering elite athlete quirks into personal nutrition plans, the Patreon is where those conversations live.