Nutrition – Are Low Carb Diets Good For Running?

What’s your power breakfast?

There’s more than one way to skin a cat.  A terrible expression, isn’t it?  I’ve had cats as pets all my life and the phrase is particularly abhorrent to me.  However it’s very apropos at the moment, because what I am about to tell you flies directly in the face of conventional wisdom about nutrition.  It’s a subject near and dear to my heart, so I think it’s worth discussing.  Now, I will add the caveat that I am not a nutrition expert by any means, but these are simply some things I have observed in myself and others.

Conventional nutritional advice suggests that we fuel our runs with carbohydrates.  There is, in fact, a bajillion dollar industry based on this idea, with sports drinks, gels, bars, and jellybeans full of carbohydrates out there on the market.  For really long runs, the typical advice is to carbo-load starting several days in advance, but even for a 5k, the idea is to take in some easily accessible carbs prior to your run.  Let’s consider why this is.

Our bodies store energy in two forms: fat and glycogen.  Glycogen is a form of glucose stored in the muscles and the liver, but it can only be stored in limited quantities.  It is easily accessible energy for intense exercise.  Fat is, well, fat and it can be stored in virtually unlimited quantities in the body.  It is a more efficient source of stored energy, but it is also harder for the body to turn fat into energy.  Your body will first use up your glycogen stores and then move on to turning fat into energy.  So the accepted wisdom says that before runs and races, consuming carbohydrates will top up your glycogen stores and give you more energy.

This is where I am going to turn that wisdom on its head.  I am a diabetic, and the kind of carbo-loading that is recommended, where the runner starts increasing their carb intake over the days leading up to a race and then takes in 30 or 40 grams of carbs in the hours before the race, is a dangerous proposition.  You might as well tell me I need to go ahead and deliberately cause damage to my feet, eyes and nervous system, not to mention my internal organs.  Because that’s what consuming that amount of carbs, along with the subsequent blood sugar rise, would do to my body.  Figuring out the nutrition before both regular runs and races has long been a struggle for me.

But it isn’t any longer, because I discovered a remarkable thing.  I actually run BETTER when I keep my carbs to the minimum.  My best races have been fueled on breakfasts of eggs, cheese and butter.  My personal record in the NYC half-marathon was fueled on a 3 egg omelet with cheese about 2 hours before the race, and one mini Luna Bar (11 g of carbs) about 15 minutes prior.  As my body has become accustomed to using fat for fuel, it has learned to do so more efficiently and quickly.  And I actually get stitches, stomach aches and some gastro-intestinal discomfort if I try to fuel up on carbs.  Refined sugar is particularly problematic and I now steer clear of it entirely when training.  No Gatorade or running gels for me anymore!

Let me be very clear that I am not advocating a switch over to a low carb diet for everyone, although I do believe that it is a much healthier way of eating.  I think what’s most important here is understanding how your body uses the fuel with which you provide it so that you can make smart decisions.  You don’t want to start something new just days before a long run or a big race.  Your body is used to your current diet and a major change before an event, even if it’s a healthy change, may not sit well on race day.  Someone whose body is used to consuming a significant amount of carbohydrate shouldn’t suddenly switch to protein and fat before a race.  Likewise, someone who has been eating low carb for several months shouldn’t attempt to carbo-load, hoping to gain more strength and energy.  Both of these strategies would inevitably backfire and you could cause yourself some serious intestinal discomfort.  You want to finish this race, not be running for the bathroom!

Many of my readers are following a low carb diet, so I say conventional wisdom be damned.  You can, in fact, fuel a great race on protein and fat.  You can also fuel a great race on carbohydrates.  Listen to your body when you run.  It will tell you what to do.

For more tips on nutrition and running, please see my post on Red-Faced Runners.

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  1. says

    Great post! I think you are right about listening to your body. I don’t think there is any right or wrong way to prepare for a run. There have been times carbs worked great for me and other times I felt icky the whole time. It’s all in what your body wants to do that day. At least that’s how it’s played out for me.

  2. says

    Great post Carolyn – everyone’s body is different and I’ve been reading about how important it is to have protein with each meal/snack. I try to give my son whole grain pasta before his races – higher in protein than white pasta.

  3. says

    Great post, Carolyn! I remember I felt (and looked) so much better when I was on a low-carb diet. I never was a runner, but I feel fuller and more energized in the day with an omelette than I do with a bowl of cheerios!

  4. Katharine says

    Thanks for the heads up that you’d posted over here. For some reason only your red faced runners post showed up in my Facebook news feed. Loved reading this entry! Once again I found myself reading and thinking “me! Me! She’s talking about me!” Since moving to lower carb, my chronic knee pain is better, I have increased stamina, and side stitches are a thing of the past. The hardest thing is knowing what to eat on the days I do a 6am workout. So far I’ve been having an almond butter squeeze pack or a mini protein/snack bar. But I’m not crazy about the ingredients in the bars. But grab and go is a must at that hour! :)

    • Carolyn says

      That is REALLY interesting, thank you for sharing. Especially the part about him getting pre-diabetes despite all the running.

  5. says

    You should read to the book Born to Run. Fascinating look at the best runners of the world, what they wear on their feet to what they eat. I think it depends on the kind of carbs too. I don’t think loading up on pasta is the best way to go by any means.

  6. says

    Interesting topic! I have a masters in nutrition, and I agree that carbohydrates are overrated as a source of energy for exercise. The marketing for gels, sports beans, and sugary drinks has convinced so many people that they “need” them to train. You’re right that figuring out proper fueling is so individualized–the ideal pre-race fuel is different for everyone!

  7. Pamela says

    I wish I had the knowledge back in my jogging days. I couldn’t jog when on a low carb diet because my energy was zapped. Thank you for your post.

  8. says

    I couldn’t agree more! I’m not a diabetic but I have noticed the same thing! I do find that towards the end of a half marathon I need something like gatorade to give me a quick boost, but before races protein is where it’s at or even a banana. No more bowls of pasta for this girl!

  9. Serena says

    Good to know- I’ve been conflicted. I follow a low carb diet to avoid diabetes (long family history of it, thus far, I’m doing well) and I swim, but I’ve really wanted to get into HIIT with running. I’m always fearful though that I might be using protein instead of fat when I’m clearly out of glycogen.

  10. says

    Amazing post! So many people are in disbelief that you can run/exercise on fewer carbs. I’ve always had more energy to exercise because of my low carb diet.

  11. Lora @cakeduchess says

    Fantastic post, Carolyn. I love my carbs too much and admire you and for your fitness level. Thanks for sharing this:) xx

  12. says

    I think it is awesome that you are a diabetic and so active. I think it is great that you found a diet that works for you… I never paid attention to my diet when I was competing alot, I probably should have. Thanks!

  13. Miranda says

    You mentioned what you ate before running a marathon – do you eat anything during the race? I’ve recently become low carb after being diagnosed with Type 1. I used to use gels and am curious about how to handle endurance nutrition on a low carb diet. I just found your blog and am excited to try many of the recipes!

    • Karen Lewis says

      I’v been training for my first half marathon. I am 42 and have type one since the age of 19. I have found that testing my blood sugar during my long runs and have a gel if need be has help prevent the after exercise low blood sugar. It was cumbersome at the beginning but I have now master it with the use of a running belt.

      • Laura says

        I am so encouraged to hear stories of people running with type 1. My 10 year old was recently diagnosed and we have just signed up to run his first 5K since the diagnosis. We are ‘training’ to see how this type of exercise affects his blood sugar. Your advice Carolyn makes a lot of sense. I would love to connect with you (or anyone else) privately to get some advice. My little runner so desperately wants to participate in this 5K without his mom whipping out his glucometer every mile :-)

        • Carolyn says

          Hi Laura…I am actually type 2 and don’t use any insulin so I am not really the best source of advice for you! Except that he can totally do it, I know marathoners who have type 1. It’s just going to be some serious trial and error for a while. And lots of glucose tablets on hand, just in case!

        • Kyle says

          As a Type 1 I constantly struggled during periods of my life where I exercised intensely. The game of reducing insulin and slamming carbs during my workouts was a blood sugar roller-coaster. I discovered that if I am on a low-carb diet that my blood sugar levels don’t drop during long work outs. No more running with a pocket full of gels or candy. No more carb loading before long training sessions.

          • Carolyn says

            Thank you for sharing that. It’s good to hear from someone who is Type 1 and has found low carb to help during exercise too!

  14. Diana says

    That’s interesting because I’ve been thinking about this quite a bit lately. I started the Couch to 5k (again!) about 5 months ago when my 3rd baby was 4 months old. I have been trying to figure out why I am zapped and can’t run more than a mile some (most?) days and others I can go for 45 minutes just fine. Annoyingly, it seems the best runs are after carb binges. Honestly after eating my weight in ice cream cake at a family reunion, I ran my first full 5k (it took me 48 minutes to run) and after the sick to my stomach feeling from being loaded with sugar passed, I felt great. Most days I try to run after a veggie, sausage omelet breakfast and I struggle. I can barely make it a mile and then walk most of the rest. I’ve tried pinning it on many variables including the weather, time of day, if I slept well enough the night before, or even total calories (I’m wondering if I eat enough especially since I’m still nursing the baby) but it usually comes down to if I’ve carb binged. Or maybe it’s all in my head because I know I’ve carb binged and NEED to run! 😉

  15. Ivana Cu says

    so many answers up there!!
    I’m a beginner in runing and I’m a diabetic. have lot of diabetic friends who run but not on lchf, so I had a lot of question you answer in these post
    I would love to contact you if I’ll have any further question before half-marathon
    greetings from Croatia!

    • Carolyn says

      Please keep in mind, I am no expert on running or nutrition. But I’d be happy to tell you what has worked for me.

  16. Dana says


    I’m gluten-intolerant and find overall that carbs and I don’t get along. Now that I’m starting to train for my first half-marathon, the carb-pushing that I find with every training guide is maddening. (I feel like garbage when I have too many carbs and lightly jog for half an hour let alone pack on the miles in training)

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