Running on an Empty Stomach

Young woman running, outdoors, rear view
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Many runners, especially those who run first thing in the morning, may prefer not to eat prior to that A.M. run. Whether this is safe or beneficial really depends on your body, your workout, and your goals.

"Fasted running" usually means running at least 6 to 8 or even more hours after consuming any calories. So theoretically, you could run fasted first thing in the morning, or in the early evening if you do not have any snacks or beverages with calories after your lunch. But should you?

Pros and Cons of Running on Empty

Pros

  • Helps avoid stomach upset

  • May improve performance

Cons

  • Reduced ability to work at higher intensity

  • Could cause overeating later

  • Doesn't promote fat burning

  • May lead to loss of muscle mass

Pros

Prevents Stomach Upset

Some people feel uncomfortable or nauseated if they have food, or liquid besides water, sloshing around in their stomach during a run. You may be able to get around this by choosing your foods carefully (for example, avoid greasy, fatty, and acidic foods) prior to a run. If everything bothers you, it's safe to do a low-intensity run of up to an hour-long on an empty stomach.

May Improve Performance

When you run without fuel, your body has to use stored energy. If you do this while you are training (occasionally), then you may see better performance during workouts and races when you are properly fueled. There are a couple of small research studies that support this theory.

Cons

Makes High-Intensity Workouts Hard

After you burn through that stored energy, you may start feeling hungry, and very likely fatigued. As some research showed, it will be difficult to keep up a faster pace and/or high intensity in your run.

Can Cause Overeating

If you don't eat before a workout, your body will keep craving calories after that workout. You may feel extra hungry and eat more throughout the rest of the day to make up for the energy supplies that were depleted while you were running—so much so that you'll eat as many calories as you would have consumed in a pre-run meal, and then some.

Doesn't Promote Fat-Burning

This is a myth about running on an empty stomach. The theory is that if you don't provide any fuel prior to your run, your body will immediately turn to fat stores for energy. However, since you have to run at a lower intensity, you won't burn away much fat (research bears this out). If your goal is weight loss, you'll burn more calories both before and even after your run with higher-intensity exercise. For that, you need fuel.

Muscle Loss

When you run fasted, your body will first use up all the glycogen (or carbs) that is stored in your muscles. When that's gone, it will turn to muscle protein. And that means losing muscle mass, usually not a welcome outcome. Additionally, the stress of running on empty may cause your body to produce cortisol, which also causes the breakdown of muscle.

How to Fuel Up Before Running

Ideally, you want to try to eat something about 90 minutes to 2 hours before running, so you have time to digest your food and you're fueled for your run. But that obviously doesn't work for everyone.

If you have been running on an empty stomach and haven't had any ill effects such as being light-headed, dizzy, low on energy or overly fatigued, you can probably continue to do it that way. However, it's smart to bring along a sports drink or an energy bar as a rescue snack in case you find yourself suddenly woozy or worn out. If you haven't been running on empty but are tempted to start doing it, bring along sports drink and/or a snack.

The answer will be different, of course, if you have a condition such as diabetes, in which case you need to discuss this with your doctor and find a good solution for your morning runs.

Always Hydrate Before Your Run

But definitely, make sure you're hydrating before you start. You'll be dehydrated because you haven't had anything to drink for however long you've been sleeping. Drink at least 8 ounces of water when you first wake up. You could drink a sports drink before you run so you know you're at least getting some calories. You should also drink water during your run if you're running longer than 30 minutes.

Before a Long or Intense Run

Some people can get away with not eating at all before a run of any distance, but you'll run stronger if you eat something before. If you're running longer than an hour or doing a really intense speed workout, it's best to force yourself to wake an hour and a half early or more (you could always go back to sleep!) for a small meal.

Eating a 300- to 500-calorie breakfast of mostly carbs will ensure you're not running on fumes. Try a banana and an energy bar, a bagel with peanut butter, or a bowl of cold cereal with a cup of milk. If you're eating less than an hour before your run, aim for a light, 200- to 300-calorie snack such as toast with peanut butter or a cup of yogurt.

If you're doing a long run and you really don't have the time or your stomach gets upset if you eat before running, try eating something small, such as an energy gel, about 30 minutes into your run.

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