Flying on Fat: How Adopting a Keto Lifestyle Transformed me into a Fat Adapted Endurance Athlete

It was just over a year ago when I was living in New York, NY and decided I’d give the ketogenic diet (Keto) a try. I was tired of my constant yo-yo dieting and the uncomfortable ups and downs in weight after years of restrictive eating, over-exercising, giving up, indulging, and repeating. I needed to heal my metabolism, but nothing was working.


With a healthy dose of skepticism and still believing claims that low- fat diets are best for healthy weight loss, I did a lot of reading and research before committing to keto. I found blogs, read books, watched YouTube videos, and found Instagram accounts as sources of inspiration to justify this way of eating. With so many people raving about their weight loss and how they felt, how could I not give it a try? In the beginning, I thought it sounded crazy to prioritize fat as a main energy source in lieu of sugar. But I trusted my research and went for it anyway.


How keto turned me into a runner – a glorious way to honor my newfound energy

Quickly after swapping out brown rice and bland chicken breast for butter, bacon, and chicken thighs I almost immediately started to feel the benefits: No more brain fog, no more anxiety, less bloat, rapid fat loss, healthier skin, longer hair, and an abundance of energy I had never experienced.


With so much extra energy, I woke up one day and decided to go for a run. This was quite the revelation because prior to fueling my body with fat, I would have never called myself a runner; I had always despised it.


While my first runs may have been slow, they were a glorious way to honor my newfound energy – it was cathartic.


I ran almost daily without an agenda or training plan or distance in mind. I was simply reveling in the beauty of how great I felt and the environment in which I ran. As my endurance increased, as did my fat adaptation, my mileage, and before too long my short 3-mile route to Central Park expanded to running around the Island of Manhattan – fasted – relying only on my fat stores for sustainable energy – and it was fun! 


Fast forward to today, a year later, and I have lost all of the weight I had wanted, I have healthily maintained it, and I have ran countless half marathons, a 40k trail race through the German Alps, the Athens Marathon, and proudly finished a self-supported 65k ultramarathon.



Targeted Ketogenic Diet and Nutrition Strategy for Long Runs and Races

Through my experience growing as a fat adapted runner, there has been plenty of trial and error with nutrition before and during long runs and races. I have found a high-fat way of eating paired with cycling carbohydrates one day pre-race yields wonderful results in sustained energy. As far as managing fuel and nutrition during runs lasting more than 3 hours, my strategy varies depending on the nature of the course.


If the course is flat, my heart rate will typically be low, therefore I will be operating in optimal fat burning mode and will not require any fuel other than electrolyte supplements every 60 minutes.


If I’m running trails in the mountains, the steep climbs will quickly deplete my glycogen stores (emergency sugar stored in the liver and muscles) and they will need to be replenished with carbohydrates to avoid what runner’s call “hitting the wall.” I solve this problem by supplementing with carbohydrates each hour. I like to carry Stinger Waffles or nibble on bananas and/or potatoes at rest stations.


Due to the anti-inflammatory nature of eating a nutrient dense, low-carb diet, my recovery after long runs is quite extraordinary. I’m often in awe of how quickly I can bounce back and lace up my running shoes or hop on the bike for active recovery within 1-2 days.



Interested in giving up bread for fats?

If you’re debating whether or not to make the switch to a fat-fueled way of eating to lose weight and/or to add metabolic flexibility as an endurance athlete, give it time. Fat adaption is a remarkable process but it takes weeks, if not months, of consistency and discipline in your diet.


I urge you to conduct your own research and read books, listen to podcasts, and seek out online resources. My favorite resources include science-backed research by Dr. Jason Fung, Dr. Jeff S. Volek, Dr. Stephen D. Phinney, Dr. Eric Berg, and Gary Taubes – journalist and co-founder of the non-profit Nutrition Science Initiative.


To follow along on my fat adapted journey, follow me on Instagram @sarah.runs.on.ketones.



Are you a runner considering running a marathon on keto?

Are you considering running a marathon on keto yourself, and could you use help with your nutrition plan? Don’t hesitate to get in touch with Lotte!


Important note to this article

This story is a personal experience! It depends on both the individual athlete and the event, if this approach is the right for you. Every athlete responds in a different way and should therefore always consult their Doctor before implementing any extreme dietary change. Results all depend on your overall body composition, which food products you implement in your nutrition plan, your training program, how long you have been fat adapted, and the duration of your race.


More successful keto endurance stories

Ultra marathoner Alfie Pearce-Higgins completed his first ultra-marathon on keto, and also shared his experiences in an article. Read it here!


How has keto changed your life for the better?

Share your story with us, send an e-mail to, or leave a comment below this article!