Do you eat before or after your run?

Many long distance runners perform at least some of their long runs in a fasted state (for example before breakfast, without taking anything), hoping that this will teach their bodies to become more effective at using fats for energy production. Even though it is not sure that it helps on race day, studies have shown indeed that you become better at burning fats if you train your body to do so.

© Mikhail Shifrin | Dreamstime Stock Photos
© Mikhail Shifrin | Dreamstime Stock Photos

The next question is then: would it help you to lose weight? In other words: would you lose more fatty tissue when you exercise in a fasted state than after a meal? Brad Schoenfeld and his colleagues have investigated this and concluded that it does not seem to make a difference. They published their study in the Journal of the International Society of Sports Nutrition in November 2014.

They divided 24 young female volunteers in two groups. One group exercised in a fasted state and the other after consuming a meal replacement shake. They all worked out on a treadmill three times a week at 70% of their maximal heart rate and followed the same diet with the aim to slim down. The women who started by exercising had their shake immediately after the workout.

After four weeks, all the women had lost weight, but there were no differences between the groups concerning amount of weight lost, waist line, lean or fat mass.

The researchers therefore concluded that it does not matter whether you exercise before or after a meal.

Schoenfeld explains the findings by citing previous research showing that our bodies change what they use as fuel, depending on what is available. If you burn more fats for a while, you will use more carbohydrates later in the day, and you have therefore to look at much longer periods than just a few hours.

You might understand their findings better if you think about the First Law of Thermodynamics, which states that energy does not get destroyed or created, but only changes from one form into another. What matter is therefore to get rid of the excess energy, whatever the form it is in.

A study with a negative result?

It is true that reading a study with a negative result is always slightly disappointing, and that is why in the past they did not get published. It is great that this now changing, because it might avoid repeating the same studies over and over again and it might also help us (I hope!) to avoid doing useless things.

Disclaimer: this article is for general information only, and does not replace medical or coaching advice. It cannot be used to guide treatment or training. If you have any concerns or questions, you should talk to a qualified health provider.


Schoenfeld B J, Aragon A A, Wilborn C D et al. Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int Soc Sports Nutr. 2014; 11 (1):54.

Spriet L L. New insights into the interaction of carbohydrate and fat metabolism during exercise. Sports Med. 2014; 44( Suppl 1): 87.

Stannard S R. Ramadan and its effect on fuel selection during exercise and following exercise training. Asian J Sports Med. 2011; 2(3):127.

Van Proeyen K, Szlufcik K, Nielens H et al. Beneficial metabolic adaptations due to endurance exercise training in the fasted state. J Appl Physiol (1985). 2011; 110(1):236.


9 thoughts on “Do you eat before or after your run?

  1. This is a debate I’ve had more times over the years than I can remember. There was a time I would never eat before a run, I’d even fast, and then I’d pick up my buddy on the way to the trail and he’d woof down a peanut butter and jelly sandwich before a two-hour run. Now there are times I will go for an unplanned run after a meal with no effects after the usual belching the first few miles. So who’s to say who is right and who is wrong? The thing I like about your post are that they are all intelligent, informative and thought provoking. I’m glad you took the time to research and post this. Thanks.

  2. The one thing I’ve learned after running a handful of marathons is that I need to get to the starting line with a full belly otherwise I’m toast, sort of, around 16 miles.

    1. You’re right. Nobody is going to advice you to race on an empty stomach. However, if you train so now and then in a fasted state, your body should get used to exercise using fats instead of carbs, which -in theory- would help you during long distances races. It is still a topic of discussion though, and it is therefore better to continue with what works for you.
      Thanks for commenting!

  3. Thank you Thank you for the highlighting the point about negative studies!!! Most people don’t realize that or how much it skews what gets published, just adding to confusion about these things. Thanks as always for a good discussion of the science. The point about shifting from fat burning to carbohydrate burning throughout the day depending on the fuel source available also speaks to one of my pet peeves, working out in “fat burning” lower intensity for a long to lose weight. I’m so glad that’s falling out of vogue because it doesn’t make much physiologic sense. 🙂

    1. You are absolutely right! We still have so much to discover about human physiology, which is fascinating. I’m sure there are more things we believe today that are going to be proven wrong in the future.
      We can only do the best we can with the knowledge we have.
      Thank you so much for your kind words and your comments.

  4. My current philosophy on this is to train on long runs in a fasted state and run in HR zone 2. My understanding is that this is teaching my body to burn fat on a run but I am fully aware that my post run meal/ drink will add the fat back on to my weight. The benefit I am looking for is to be able to run a marathon – or my first ultra, without hitting the wall by changing from burning carbs to burning fat, as I will be burning fat from the start. What do you think?

    1. That is indeed what many scientists hope will happen, but there is not that much evidence that it really does. As you will give your body enough carbs on race day, it will spontaneously go back to burning carbs, as it uses the fuel which is available.
      There is however a study on rugby players showing that they did much better after Ramadan (= plenty of training in a fasted state).
      This is a debate that will go on and on and on, as it so difficult to conduct a good study.
      As you say yourself: experiment, and listen to your body!
      Good luck to you.

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