Last week, I shared some of the signs that can tell you if you are mostly burning sugar or fat as an endurance runner.
One easy tool to test what your body is burning is to implement fasted runs. There are mixed opinions on this- whether it forces your body to burn fat or if it is only burning muscle (not want you want) but in either case, it does force your body to workout in a glycogen depleted state where it has minimal sugars to pull from.
To be clear, fasted runs do not teach your body what to burn but they can help you identify if you are a sugar burner or not.
A fasted run is not simply running on an empty stomach. To be glycogen depleted, first thing in the morning is ideal. Otherwise, you would have to wait 5+ hours after eating and are more likely to feel hungry and weak.
Fasted runs are NOT:
- a way to lose weight
- a short cut to fat loss
- guaranteed to boost your training results
However, they do have many helpful functions.
- By forcing your body to work out in a glycogen depleted state, you mimic how running will feel toward the end of a longer race and teach your body to pull from fat stores as opposed to running out of sugar and bonking
- If you cannot go more than 2-3 miles without feeling weak and shaky, you can be pretty confident that you are primarily a sugar burner and need to tweak your diet.
- If you do a few long runs in a fasted state, your body learns to work hard without the benefit of fuel which often means an improved performance when you are fueling with carbohydrates on race day
- Research shows that exercising in a fasted state increases lipolysis and fat oxidation rates.
I use fasted runs several times a week. Most of my short distance runs are done immediately after I wake up. I drink water and go out the door.
If I wake up hungry or have an especially long or hard speed workout, I usually eat 1/2 a banana with almond butter as I know I will perform better.
I also incorporate fasted long runs up to about 16-17 miles a few times per cycle. I typically alternate a glycogen depleted long run with a fueled long run so my body learns to work with whatever it’s given.
Years ago, when I used to fuel on anything over 6 miles, I found that my body would start to shut down every 30-40 minutes and crave the sugar boost. That was a key sign for me that I was too dependent on sugar as fuel. Since changing my diet and incorporating more fasted runs, I feel fine without fuel.
However, I do want to add that if body composition or fat loss is a goal, you will see faster results with less cardio (skip the marathon training!) and more strength training and HIIT workouts. Steady state cardio is known for making it difficult to maintain muscle mass and encouraging fat storage.
Do you use fasted runs?
Have you ever done a long run in a glycogen depleted state?
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