Using Stored Fat as Fuel

A couple of weeks ago, I posted about how to fuel for intense workouts. I discussed how to fuel before, during and after an intense workout.

I recently read an interesting article in the July 2012 issue of Runner’s World about training while being carb depleted. The basic premise of the article is to “train low, race high” meaning train low on glycogen then race fully topped off.

Here are some main points to using stored fat as fuel:

  • Your body can hold onto about 90 minutes of stored glycogen, which is mostly in the muscle and liver. Keep in mind that your brain needs glycogen; when glycogen is depleted you will hit the wall.
  • Your body has more than enough stored fat to provide fuel. By running slow and staying in an aerobic (with oxygen) state you will burn mostly fat. Once your body goes into anaerobic (without oxygen) state, running faster, it will burn glycogen.
  • By training your body to use stored fat as fuel, you will increase the capacity of stored glycogen and teach your body to use the glycogen more efficiently.
  • You will want to refuel with carbs and protein immediately after the fasted run.
  • The few days to a week leading up to your race you will want to carb load and drink plenty of water. Eat a light breakfast that incorporates all of the macronutrients 2 hours prior to the race and fuel during your run.

Here are some ideas from the article about how to run on empty:

  • Run in the morning before breakfast and after fasting for 10 hours or more.
  • Do a hard workout in the morning then run in the afternoon without eating carbs between workouts.
  • The magazine also stated that it takes an hour of fasted running before your body starts to burn fat.

Train on Fumes from Runner's World

Couple of key points:

  • This is not a low carb diet.
  • It’s a good idea to carry an emergency gel on your long run.
  • Consider drinking a no or low-carb electrolyte drink to prevent hyponatremia during your long run. A good example would be to use nuun.

Now, I know this is pretty much the complete opposite of what I posted before, but that is the great thing about nutrition. There are different methods/diets to get the job done. You really have to figure out what works for you and your body and stay consistent.

Red heart

What are your thoughts about fasted runs?

Have you ever used this fueling strategy in any of your races?


  1. There is no way I can run without any energy in my belly!

    1. It doesn't bother me too much. I think I would have a harder time not eating during a long run.

  2. Wow- that's really interesting! I'd have a hard time avoiding carbs... but I always like reading nutrition/running research. Thanks for sharing!

    1. I think it's interesting too. I love experimenting with nutrition and running. I would have a hard time avoiding carbs too. Running immediately after I wake up would be easier for me. Then of course refueling with carbs and protein.



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