Last week I mentioned that more often than not, I run fasted. I have been training and racing on an empty stomach for the past two years. I think 2013 was the last time I tried to eat before a race and it just didn’t end so well.
I want to preface this post by saying I’m not a nutritionist, doctor, trainer, professional (in any sense), so please take this all with a grain of salt. If this is something you are truly interested in trying, I highly suggest you consult with someone with a lot more knowledge than myself. But keep in mind, what works for one person doesn’t work for everyone.
Although I will mainly talk about my personal experience, I did want to talk about the science behind “fasted running”. The idea behind running on an empty stomach, or going on “fasting runs” is to train your body to utilize available fuel more efficiently. This is especially beneficial for endurance athletes who want to avoid “hitting the wall” or “bonking”.
Why Run Fasted?
Our bodies rely primarily on carbohydrates to produce energy. Carbohydrates (or our bodies energy) is stored as glycogen which is broken down during a workout or a race to be used as fuel. While this all sounds good – our bodies can only store so much glycogen, so once those glycogen stores are diminished, our bodies turn to breaking down fat, which is a WAY less efficient fuel source. This is when we “hit the wall”.
By fasting before a run, we start teaching our body to burn fat more efficiently. Because we have a lot more available fuel in our body in the form of fat (just not an efficient process), training our body to use that fuel helps with endurance and aerobic performance, and avoiding “the wall”.
How Should I Start?
Start after an overnight fast. This was easy for me because I’m a morning runner. Once you get up and get out the door, your body doesn’t have time to register that it’s hungry for fuel. Because glycogen stores are already low, our bodies are forced to burn fat for fuel. So after time, our bodies become more efficient at utilizing fat for fuel.
You should also start by incorporating this into your easy/recovery runs. Do not start by racing fasted or trying a track workout fasted. For me personally, I have always kept my speed work for the afternoons, after I do have fuel in my body. I find I am more able to hit certain paces and maintain a higher intensity for longer.
So What’s Bad About Training Fasted?
Training in a fasted state usually means you won’t be able to run as fast in training. To break down fat you require more oxygen and it takes longer to break down so therefore you usually end up running slower. If you notice, a lot of my mid-week, mid-distance runs are about 60-90 seconds slower a mile than my race pace. Running hard while fasted is especially taxing, and I really only reserve that type of stress on my body for race day.
And For Me…
I started running fasted for two reasons. 1. I’m a morning runner but didn’t want to get up any early to eat before hand and 2. I have a stomach that does not handle food well before running (especially hard or for long periods of time).
When I first started training for my first marathon in 2011, I would munch on some saltines and peanut butter before heading out for any run lasting more than an hour. What I found was my body felt sluggish, I would cramp up, and I just felt “heavy”. I started to research what are the best things to eat before a run and I stumbled upon the concept of fasted running. I decided to give it a try, so the next morning I woke up, didn’t eat, and went out for a 7 mile run. I found myself feeling lighter, I didn’t cramp, and shockingly, I felt like I had more energy. From then on, I never ate before any training run. I continued to eat before half and full marathons, as I had only been following a “fasting running” training plan for a few months / I still had no idea what I was doing.
From my first marathon in 2011 to my third in 2013, I ate saltines before the race start. Although I didn’t get the same “heavy” feeling as I did with other foods, I still didn’t feel as great as I did on my training runs. But I was too nervous to not eat before such a long distance.
The first marathon I raced fasted was in 2014. I have had a lot of personal success with training and running fasted. It is something that has taken me YEARS to understand and “master”. I have that in quotations because I am still playing with what works best fueling wise. Because I don’t eat before I run, I have to focus a lot on hydration and my nutrition leading up to a race. I tend to drink a ton more water before I head out for a particularly long training run and continue to do so while I’m running. Nutrition wise, I make sure in the days leading up to the race, I’m fueling my body with lots of complex carbohydrates, a good amount of protein, and a good amount of “good fat” – think nut butters, avocado, etc.
Some people have asked if I ever get hungry when running fasted – particularly for my 20+ mile training runs. I am usually up around 6, out on the road by 630, and done by 915. That’s a lot of calories burned and no fuel for a long time. When I initially started training fasted, I would feel hungry while running, it was because I didn’t fuel properly in the days leading up to a long fasted run. Now, I can head out on the road for 3 hours and not once feel hungry. It’s amazing what our bodies are capable of doing.
While this method of training works for me and has only benefited me in my training, it is not for everyone. I know some people who HAVE to eat before they run, and that is okay! It’s so important to listen to your own body and know what it needs to get through a 20 mile run.
I wanted to do a high-level overview as to not get too complex on the science of it all. Although, I do love me some science. If you guys have any other questions, or want me to go into more detail about something specific (science or personal wise!) please let me know!
I also think these articles are great resources for learning more about fasted running:
Should You Try Fasting Before Running
Train Your Body to Fuel Efficiently with Fasting Runs
Training in a Fasted State
The Science of Bonking and Glycogen Depletion
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