Should I do fasted cardio?

Pre-race breakfast

What happens if you run or exercise on an empty stomach?  What are the potential benefits?  Is there a downside?  There has been a lot of talk about fasted cardio and becoming “fat adapted”.  Personally, I find it hard to run on an empty stomach, but I have been curious about the overall benefits.  Could it lead to better athletic performance?

Fasted cardio is when you exercise, usually first thing in the morning, on an empty stomach in a fasted state.  If your glycogen stores are depleted, your body has to use a different source to fuel your workout….fat.

From what I’ve read, the purpose of doing cardio in a fasted state is to train your body to use it’s fat stores for fuel.  Basically, burning more fat for fuel versus burning the carbohydrates from the food we just ate.

The primary reason I found this interesting is that burning fat for fuel would come in handy while running long distances.  I’ve only run four marathons, but I’ve found it hard to find the perfect fueling strategy.   Could I avoid “hitting the wall” during a race by training my body to use fat for fuel?

When trying to train your body to become fat-adapted, you must do some “glycogen-depleted” workouts.  (Glycogen is a stored form of fuel for the body)  This means to do an early morning run with no food before or during.

While fasted runs can help the body adapt to effectively burn more fat for fuel, it probably won’t improve your endurance or aerobic conditioning.  According to Lauren Antonucci, RD, you can train your body to burn more fat than carbohydrates, but for most people you won’t see any long term athletic benefits.

Here are some findings in an article from Medicine & Science in Sports & Exercise:

“depletion of carbohydrate stores is associated with fatigue in the form of reduced work rates, impaired skill and concentration, and an increased perception of effort”

“carbohydrates provide a key fuel for the brain and central nervous system”

“there is significant evidence that the performance of prolonged sustained or intermittent high-intensity exercise is enhanced by strategies that maintain high carbohydrate availability

Another reason that fasted cardio might not be the best choice, as stated by health and fitness expert Pete McCall, is that “it could cause the body to burn protein for fuel, which would reduce the amount to be used to help build and repair muscle tissue.  If carbs are not available for energy, the body can convert proteins for fuel, which leaves fewer proteins available to re-build muscle post exercise.”  

I have also come to find that individuals who are fat adapted still need to ingest some form of carbohydrate during endurance races.  If this is the case, what is the point really?

I guess in the end it all depends on your goals.  If you are looking to lose weight, then this strategy may work for you.  According to Women’s Health magazine, some studies found that exercising while “fasted” can burn up to 20% more fat than if you ate before exercise.  (With that said, I believe weight loss comes down to overall lifestyle changes that are sustainable and not trying to “force” your body into burning fat).

Fasted Cardio. Should I try it? Is it right for me? Click To Tweet

Some people prefer to exercise on an empty stomach or just don’t have time to eat before an early morning run.  If this is the case, it’s important to pay attention to how you feel, as far as energy levels, nausea, or feeling light headed.  You don’t want to struggle during your runs or workouts.

Personally, I like to eat something before running.  After discovering that there is most likely no potential benefits in athletic performance, I will continue to do so.  I feel that even just a small amount of food gives me more energy and makes my run more efficient and enjoyable!

As for fueling for my next marathon, I will be relying on carbohydrates.  Through trial and error, I will find what works best.

Do you exercise on an empty stomach?

Have you become a fat adapted athlete?  I would love to know if anyone has had positive results using this strategy!



8 Responses to Should I do fasted cardio?

  1. I also like to eat and have coffee before my workouts. I have never really tried to run on an empty stomach before. Wonder how it would go?

  2. Kimberly G says:

    If I work out in the morning, I always do so without eating. It’s hard for me to workout on a full tummy, especially when running!

  3. Great post! Most of my runs are at 5:30 AM and since my GI system would never cooperate with eating and running soon afterward, I skip eating. If I’m heading out for a long run I do make the exception to eat something and I make sure to take fuel along with me. I ran 40 marathons using the same strategy so I think it’s safe to say that works for me. 😉

    • Cyndi says:

      After running 40 marathons, I think you have it figured out! I hope to find the right strategy for my next marathon:)

  4. This is such a great post! I think this is such an individual preference because I know some people who just don’t feel well exercising on an empty stomach, but I personally love working out on a near empty stomach first thing in the morning. I think it’s something you have to train your body to do, but can be very advantageous for running.

    • Cyndi says:

      Thank you! I know I like to eat at least a little something before running. But yes, it depends on preference. I agree that you can train your body and adapt.