Effects of a high fat, low carb diet on a female distance runner: a case study

The seed was planted on my flight to New Zealand when I listened almost exclusively to Endurance Planet, a podcast about training and nutrition. They are super into high fat, low carb diets (HFLC) for endurance athletes. And I was so confused! Like, I thought carbs were the answer to my life in terms of training and racing. But then I was slapped in the face when I heard that maybe you don’t actually need carbs and you should eat a ton of fats, including BUTTER of all things. Everything I had assumed I knew about nutrition kind of exploded. So I spent all of my extra time (and procrastinated doing actual homework) doing what every 21 year-old does on the internet…I spent hours looking for published studies on HFLC diets for athletes. I listened to more podcasts. I talked with my professor of Exercise Metabolism. I emailed my mom papers I found asking for her thoughts. But what I realized after all of my research and inconclusive findings was that I could just try it for myself. Because diet is such an individual thing, and what works beautifully for one person might make another person feel like a deflated elephant.

So for the past three weeks, I have been eating a very low carb, very high fat diet.

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Chard and carrots sautéed in grass-fed butter, topped with a fried egg
a low carb ‘pancake’ made with grated carrot, an egg, and protein powder, fried in coconut oil and topped with ricotta and peanut butter
silver beet sautéed in olive oil, topped with beets, avocado, hemp seeds, brie, tuna, and tahini

And if this was a lab report, here is my results section:


  • For the first week, I felt really really terrible on all of my runs
  • I found it difficult to get my heart rate up, which made circuit workouts really frustrating
  • During week 2, I would feel noticeably better during my run around minute 20
  • The volume of my meals was much smaller because of the caloric density of high fat foods, but this was sad because I really enjoy eating
  • I’m pretty sure all of the eggs I was eating made me break out
  • On week 3, I was feeling better on my runs earlier and feeling less hungry during the day
sunrise run to the beach; a lovely, fasted 8 mile slog fest
a prime example of how smiling in a picture does in no way mean that I felt good on my run


One big takeaway from this experiment worth mentioning is the conquering of this ingrained ‘fat-phobia’ that our culture still perpetuates. We all know that healthy fats really are good for us, but we still have a little voice in our heads telling us that they are bad and make us fat. So when my goal was to actually eat mostly fats, I had to get over that really quickly. No more ditching the egg yolk, using nonstick spray instead of oil, and being mindful of how large a tablespoon of peanut butter really is.  Even if my body isn’t even a little more fat-adapted after the past three weeks, I still consider this a win. I have proved to myself that fats don’t make you fat.

I knew when I started that it would not be a sustainable lifestyle. The goal was to see how I felt and force my body to adapt to becoming a better fat burner. But no way would I be able to do any sort of high intensity workout if I was to maintain this eating style. I also met with a nutritionist last week who specializes in sports nutrition. Fat burning adaptation definitely has its place (such as the ‘train low’ approach, google that one!!) but for the majority of my runs, I think it is more beneficial to have full glycogen stores.

I am now planning on reintroducing carbs starting this Monday. I am looking forward to increased energy levels and effortless runs. And pancakes. I really miss pancakes.

my first time at Capers…will definitely be heading back there this week 

**Note to the reader-> please feel free to ask any other questions you may have regarding my HFLC experiment. I am also very curious if anyone else has tried this and how you felt. Let me know!


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