Running on an Empty Stomach

Many runners, especially those who run first thing in the morning, may prefer not to eat before that A.M. run. Whether running on an empty stomach is safe or beneficial really depends on your body, your workout, and your goals.

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

Advantages of Running on an Empty Stomach

Although fueling yourself is critical for exercise performance, there are some advantages to running on an empty stomach. This is particularly true if you have a sensitive stomach.

May Prevent Upset Stomach

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) before a run. If everything bothers you, it's safe to do a low-intensity run of up to an hour on an empty stomach.

May Improve Performance

When you run without fuel, your body has to use stored energy. If you occasionally do this while you are training, 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.

Disadvantages of Running on an Empty Stomach

While there may be some benefits to running on an empty stomach, there are also important drawbacks to consider. Especially if you haven't fueled recently, you may find there are more disadvantages than advantages to running on an empty stomach.

Makes High-Intensity Workouts Harder

After you burn through that stored energy, you may start feeling hungry and very likely fatigued. As some research shows, it will be challenging 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

The idea that fasted running promotes more fat-burning is a myth. The theory is that if you don't provide any fuel before 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 much fat (research bears this out). If your goal is weight loss, you'll burn more calories both before and after your run with higher-intensity exercise. And that likely means you'll need fuel before your workout.

May Lead to Muscle Loss

When you run fasted, your body will first use up all the glycogen (or carbs) stored in your muscles for energy. When that's gone, it will turn to muscle protein, and that means losing muscle mass—not usually 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 eat 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, especially if you run early in the morning and don't have time for that lengthy digestion process.

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 in case you find yourself suddenly woozy or worn out. If you haven't been running on empty but are tempted to try it, bring along a sports drink and/or a snack just in case.

Always Hydrate Before Your Run

Make sure you're hydrating before you start. You'll be dehydrated because you haven't had anything to drink for as long as 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.

Fueling 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. 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 the following breakfast ideas:

• Banana and an energy bar
• Bagel with peanut butter
• Bowl of cold cereal with a cup of milk
• Bowl of yogurt with berries
• Oatmeal with milk and banana slices

If you're eating less than an hour before your run, aim for light, 200- to 300-calorie snacks. Try these:

• Toast with peanut butter
• Cup of yogurt
• Grapes with a few almonds
• Banana and walnuts
• Cottage cheese with apple

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.

A Word from Verywell

While there may be some advantages to running on an empty stomach, it’s generally a good idea to go into a run adequately hydrated and fueled. Weigh the advantages and disadvantages of running on an empty stomach for your lifestyle and training goals. If you do experiment with it, be sure to fuel up afterward so that your body can replenish and recover properly.