Using Fat as Fuel

Lately, the hungrier I am in the morning, the more ready I am to get out for my run. Does that sound crazy? You didn’t misread it. I’ll reiterate: my morning hunger pangs are now a signal, not to take out the pot and milk for some oatmeal, but to lace up my shoes for a run. The reason for this is that I have been enhancing my body’s ability to utilize fat to fuel my running instead of glycogen (Note: Glycogen is stored glucose and glucose is produced from carbohydrates. All three are different, but they are often used somewhat interchangeably. In this post, I may use all three terms.).

Not my picture. Not positive on the accuracy, but you get the idea!

Why am I running when hungry or rather, why am I running before eating anything? Allow me to share…

There are two sources that runners tap into for running: fats and glycogen (built up from the macronutrient carbohydrates). Throughout the large majority of my years running, I have been using glycogen as the source to get me through my runs. When I was a sprinter in high school, I had no choice; the body doesn’t have the ability to burn fat for such high-intensity efforts so it will always be using glycogen as fuel in these cases. When I transitioned to 5k and 10k running, I also was using glycogen as fuel although this is when I could have began to train my body to use fat as fuel had I even known the body had two options.

Since I thought carbs were the only nutrient that what gave the body so much energy to use, I was an easy target for GU products. It didn’t take too long for me to get used to the texture of the energy gel so before long, I was buying GU gels quite regularly. I couldn’t even tell you that I needed the extra boost or if I even consciously thought about needing the energy. I really think I just had no idea that I could be using already stored up glycogen or fat to get through my 5-6 mile runs. But of course, if you give a body sugar, it will crave more sugar. And when gel companies put flavors such as Peanut Butter, Chocolate Outrage, Espresso Love, Strawberry Banana, and Vanilla on the shelves, it’s too tempting to feed the least for me.

For all the reading I did in preparation for my first marathon, I’m surprised and disappointed I didn’t read about fat as fuel. I mean, I consumed articles and YouTube videos daily so I could nail a Boston Qualifying (BQ) time in my first marathon (didn’t happen). I trained like an animal. I ate like an animal. And I wanted to run and eat like an animal, at least a small one. Given that I had just just read Eat & Run and started practicing Scott Jurek’s advice of learning to eat while running, I thought I had unlocked the key to avoiding “the wall” which is caused by bonking, which is in turn caused by a depletion of glycogen that causes to body to slowly shut down or in computer terms, to hibernate.

I’m not a medical professional or a scientist, but from reading a lot of material out there, I can confidently state that the body has enough glycogen (stored up glucose) to fuel a runner for about 2 hours of activity give or take 30 minutes depending on the individual’s health and diet and the intensity level of the run. For the marathon, I knew this meant feeling depleted of energy around mile 18 so I thought I could avoid bonking run by running with an Amphipod waist pack filled with high glycemic, sugary foods such as orange slices, pretzels, dates, and even a Clif bar that I would consume at designated times. Was I right? I suppose, although I was nowhere near goal pace. I didn’t bonk. Instead, around mile 22 I started to feel the beginning calf twinges of possible cramping because I was not hydrating properly. For all of this work though, I could have been using fat as fuel and not worry about trying to run 7 minute miles with nearly 5 pounds bouncing around my waist.

The straw that really broke the camel’s back though occurred this past July at my ultra. The race was a 12 hour run around a nearly 11 mile loop course which I had a blast running. This isn’t a race review so I’ll spare you the details. What I will tell you though is what I relied on for energy: energy gels (wayyy too many of them), banana quarters, and Pringles for sodium (this was the first time I’ve had Pringles potato chips in well over 5 years and boy oh boy did I down those chips–You know how it is: Once you pop…). Back to those gels, though. I must have had at least 10 gels that I can remember. These high sugar gels and other sugary foods I snacked on occasionally, did not bode well for my stomach after the race. I had the worst GI issues I’ve ever experienced in my life and I blacked out on the ride back, likely from a serious crashing of my system which the high sugar overload certainly didn’t help.

Since that day, I decided to start training my body to better utilize fat as fuel. How? By doing just what I described in the beginning of this post. And by slightly increasing the fat in my diet (No..not a low-carb, high-fat diet. I practically live on potatoes and bananas for crying out loud!). By running all of my runs, especially the long and/or aerobic ones, in the morning before eating anything, my body is forced to tap into fats to keep it going. When training for July’s ultra, I would take in a gel after 90 minutes of running like clockwork. Now, I can run 2 1/2 hours – 3 hours without taking in any food, solely water with an electrolyte tablet. Even for my track workouts, I know I have enough glycogen to get me through the workout without the need of any gels. I know this ability is going to greatly help me during future ultramarathons and I’m quite certain, and hopeful, that it will assist me in next month’s marathon as well.

Wrap-up note: When you rely on sugar, your body wants it more. And more. And more. For long-distance running, the evidence shows this just isn’t the best way to fuel. There are so many more calories from fat available for endurance runners and athletes so why not tap into them? This is what I am trying out now. I’ll let you know in October post-marathon how I fared from using this method.

How do you fuel? Carbs or fats? What types of foods? Let’s talk in the comments!

Some YouTube videos that discuss fat as fuel:

Some helpful references:


4 thoughts on “Using Fat as Fuel

  1. I run all my morning runs without food. However, I’m not training for a marathon, so my morning runs top out at about 10 miles right now. I do start feeling hungry at about mile 8, but by then I know I’m almost done so I just keep on running. My morning easy and long runs are at about a 9 minute pace, so that puts me with no food for at least 90 minutes. My hubby trains without food as well, and he’s on a quest to qualify for Boston. Maybe he’ll chime in on here as well.

    Liked by 1 person

    • That’s so great that you’re using this method. I really do stand by it. I know my post made it seem like I’m trying it out on a whim, but I’m really not. I’ve never tried it out for a marathon. Otherwise, I know it’s the best for long-distance running. Feeling hungry is totally fine. I don’t want to speak like the no-all, be-all, but I think if you kept it up, you’ll start to not feel the hunger until later and later which is awesome. It’ll mean you’re body is adapting and really starting to use the fats. Do you eat a good amount of fat in your diet? I’d love it if your husband chimed in. Invite him into the community! Oh, and if this comment posts as Plantrunner, it’s still me at Eat, Run, and Done. I’m still working out some kinks 🙂


  2. Pingback: My Marathon Experiences | EAT, RUN, AND DONE.

  3. Pingback: Portland Marathon Recap | EAT, RUN, AND DONE.

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