Should I Eat Before I Run?

Female eating granola bar with sun behind her

The age-old question: should I eat before I run/cycle/swim? This is one of the most common questions I get from clients who are currently active or who are starting a new workout regimen. 

There are a lot of different opinions about when, how much, and what types of foods you should eat before a workout.  And, the truth is, there is no one right fueling strategy that works for everyone.

Add to that the fact that different types of workouts have different fueling requirements, and it’s no wonder people are confused.

The fact is, though, that if you’re ignoring nutrition as an integral part of any exercise or training program, you will not get optimal results and may even do more harm than good.

In this post I will explain the scientific reasons behind different fueling strategies and how to integrate them into your routine.

First, let’s clarify what I mean when I use a few key terms, then we’ll dive into the details.


Fasted state = nothing consumed except water within 6-8 hours.  Usually, exercise done in the fasted state is done first thing in the morning after fasting overnight.

Low-intensity exercise = gets your heart rate up and you’re breathing a little faster, but not to the point of not being able to speak. (25-30% VO2max(4)).

Moderate-intensity exercise = you can speak, but not full sentences. (50-60% VO2 max(4)).

High intensity exercise = you’re breathing hard and speaking is difficult (>75% VO2 max(4)).

Why eating before a workout is important


Food is fuel.  Just like your car or your cell phone, if you want your body to work for long periods of time, you need to give it fuel.


Significant evidence supports fueling strategies that maintain sufficient carbohydrate availability for enhanced performance with sustained and/or high-intensity exercise.  This includes sessions with intermittent high-intensity bouts, such as high-intensity interval training (HIIT).(3)

Training Adaptations

An integral part of athletic training is adapting the body for more efficiency and flexibility with using different nutrients for energy.(3)

In general, carbohydrates are your body’s primary source of fuel.  That said, your body also always uses fat and protein as energy sources to varying degrees.  The rate at which your body uses fat and protein at any given time depends on how much carbohydrate is available and your activity level.

Your body can store a limited amount of carbohydrates in the liver and in muscles.  The storage form of carbs is called glycogen.  When you have not eaten for a long period of time and glycogen stores are depleted, such as overnight, your body will use more fat for fuel.

Additionally, intensity and duration of exercise impacts what types of fuel we use.  During high-intensity exercise, your body uses mostly carbohydrates for fuel.  On the other hand, low- to moderate-intensity exercise shifts the body to burning more fat for energy.

How much more fat will you burn during lower intensity exercise?  That depends on how well trained you are.  Well-trained endurance athletes get the most energy from fat during exercise(4), indicating that your body becomes more efficient at using fat for fuel the more training you do. 

Why is this important?  Well, when participating in endurance sports, energy and performance significantly drop when your glycogen stores are depleted.  When your body can use more fat for fuel, glycogen is not depleted as quickly, so you don’t “hit the wall” as early.

In addition to athletic training, studies have shown that there may be nutrition strategies that can help push your body to more fat-burning efficiency.  Some studies suggest that doing low- to  moderate-intensity exercise of less than 60 minutes in duration in the fasted state may help push the body to burn more fat, thereby speeding up fat burning adaptations.(1) This strategy comes with the risk of under-nourishing your body, though, so beware.

It’s important to note that the research isn’t conclusive as to whether exercising in a fasted state actually produces performance benefits.(3)  We also don’t advise exercise for longer than 60 minutes without fueling.  As with any nutrition plan, it’s important to take what we know and figure out what works for you.

Bar graph showing how various energy sources (plasma glucose, plasma free fatty acids, muscle triglycerides, and muscle glycogen) are used at 3 exercise intensities - 25%, 65%, and 85% of VO2max.

Types of fuels used for energy change as intensity increases. Note: Plasma Glucose = blood sugar, Plasma FFA = fats in blood, Muscle TGL = fats in muscles, and Muscle Glycogen = sugar in muscles. (From Romijn JA, et al. (1993) Am J Physiol)

When is it ok to skip pre-workout fueling?

As with everything related to sports nutrition, the simple answer is it depends.

First, as previously mentioned, you should fuel any exercise longer than 60 minutes with a pre-workout snack or meal within 3-4 hours of your workout.  You should properly fuel any high-intensity exercise as well. I recommend at least a small snack before moderate-intensity exercise as well.

That leaves low-intensity exercise for less than 60 minutes.  Generally, it is ok to not eat before one of these workouts with a few exceptions.

  1. You are prone to hypoglycemia.  Ideally, you would have a meal or snack 1-4 hours prior to exercise.  If you don’t have an hour to wait, try having some protein with your pre-workout carbs.  Protein slows the rise in blood sugar and, therefore, how much insulin the body releases to lower blood sugar.(2)
  2. You might have trouble meeting your calorie needs for the day.  It is important for overall health and performance to ensure sufficient calorie intake throughout training.
  3. You are doing high volume training.  What constitutes high volume training will depend on the individual, but during periods of high volume, any missed opportunity to eat could easily lead to insufficient calorie intake for the day.

Different workouts require different fueling strategies

Eating before high-intensity workouts

  • Carbs: 1-4 grams per kilogram of body weight (0.45-1.8 grams per pound). (3)  This is a wide range and your needs are going to depend on many factors including your fitness level, age, and environmental conditions.   To figure out what you need, start at the low end of the range for shorter workouts and gradually add more for longer or more intense workouts. Play around with it until you find the levels that feel right in terms of energy and tolerance.
  • Protein: Break-down and absorption of protein takes more time and requires more energy than carbs, and it can accelerate dehydration.(4)  There is also no evidence of performance benefits or improved muscle development from pre-workout protein intake.(3)  For these reasons, we don’t recommend a lot of protein before a workout.  Stick to no more than 10-30 grams (adjust for your weight and tolerance) within 4 hours before a workout.(1)   
  • Fat: Like protein, fat is digested and absorbed more slowly than carbs.  Avoid high-fat foods within 4 hours of a workout to avoid gastrointestinal (GI) discomfort.

Eating for low- to moderate-intensity workouts

  • Carbs:
    • >60 minute workout: 1-4 grams per kg of body weight (0.45-1.8 grams per lb). (3)  This is the same as for high-intensity workouts, but keep in mind that the longer and harder you work out, the more fuel you need.  Start at about half the amount of carbs you would have for a high-intensity workout of equal duration.
    • <60 minute workout: avoid a lot of carbs in your pre-workout snack. (1)
  • Protein:  10-30 grams.  When doing a low- to moderate-intensity workout, the negative effects of pre-workout protein aren’t as noticeable.  A little protein can quell hunger without impacting how much fat your body uses for fuel. (1) 

Key Take-Aways

As with all things nutrition-related, there is no one-size-fits-all strategy for fueling your workouts. 

In general, pre-workout fueling should focus on optimizing carbohydrate availability for most workouts. 

There is a pretty wide range of recommended carbs (see above).  If you aren’t sure what works for you, start at the low end of the range and adjust up gradually over time.  You should also adjust carb intake for each workout based on duration, intensity, and environmental conditions.

Protein is most beneficial when eaten post-workout.  Large amounts of protein pre-workout can lead to GI distress and dehydration, particularly for long or intense exercise.  That said, a little protein before your workout doesn’t hurt if you are able to tolerate it.

In general, avoid fatty or high-fiber foods within 4 hours of long or intense workouts.  Like protein, these foods are digested slowly and can cause GI issues.

Finding the right pre-workout fueling strategy for you will take a little trial and error.  Be patient, make adjustments gradually, and listen to your body. What works for someone else might not work for you.

Whew, that was a lot of information!  Feel free to leave a comment below or send me a message with any questions. 

Also, I’m working hard to put together a great pre-workout snack guide! Join my email list below to be the first to know once it’s ready for download.


Leave a Reply

Scroll to Top