How fat can fuel you through an ultra marathon

Alfie Pearce-Higgins

Is it possible to complete an 85-mile run (137 km) in unforgiving terrain on a low-carb, high-fat diet? Apparently so; Alfie Pearce-Higgins amazingly finished in fifth place in the Oman by UTMB ultramarathon.

The Telegraph: Bringing home the bacon: what happened on my first low-carb ultra marathon

Alfie had met with Professor Tim Noakes a few weeks prior to the race, and learned about running on an alternative fuel: fat. Most athletes (and let’s be frank, most people in general) believe that runners need to load up on carbs for fuel. Professor Noakes told Alfie that there is no benefit in eating carbohydrates; instead, he should focus on fat as his fuel source.

Alfie followed Professor Noakes’ recommendation and switched from his usual sugary cereal and grains to veggies, meat, and butter. This change transformed him from always being hungry to only eating three times a day and feeling totally content and energized. His body had gone from running on glucose to running on fat.

Finally, it was time for the big race. Half of the runners dropped out of the race but Alfie flourished. He required only a fraction of his usual amount of food during a race, munching on whole foods like nuts, bananas and dried meat.

After 23 hours, Alfie made it to the finish line way ahead of many of the other more experienced runners. In this 23-hour race, he had burned nearly 20,000 calories. He explains:

I estimate that I ate 3,000 [calories] during that period – which is only 500 more than the normal recommended daily allowance for a man. The reason, according to Noakes, that my body could cope with this deficit is because I had trained it to run on fat rather than carbohydrates. A mere 2.5 kg (5.5 lbs) of body fat would suffice to make up the difference; true to form, when I weighed myself, I discovered that I was indeed a couple of kilos lighter.

Does this mean all runners and endurance athletes should ditch the carbs and turn to a low-carb, high-fat diet? Well, everybody is different, and what works for some may not work for others. But based on Alfie’s experience, a trial is in order!


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  1. 1 comment removed
  2. Jay Baggett
    Looking at this for long backpacking trips. Running the dehydrator right now to see what might work weight wise.
  3. Jeff Davis
    Makes a lot of sense. One question, from the article it sounds like this runner became fat adapted in only 2 weeks. Is that correct?
  4. Billy
    He certainly didn't get fat adapted in 2 weeks. Is this a make believe story?
  5. Gentiann
    I'm reading 6 weeks in the original article, not 2 weeks.

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