Why Runners Need Carbs

Trinh Le, MPH, RD
by Trinh Le, MPH, RD
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Why Runners Need Carbs

You’ve laced up your running shoes, fired up your tunes and are ready to nail your run. But did you remember to get your carbs in? Yes, they get a lot of flack in certain circles, but carbohydrates can be the most important nutrient on tough training days. Here’s the low-down on how your body fuels up and uses carbohydrates for energy.


Carbohydrates, specifically glucose, keep you going during a run. Glucose is converted into energy that contracts exercising muscles — the faster and longer you run the more glucose you use. Key things to know about glucose:

  • Glucose is needed for you to optimally burn fat during your run. During long runs, fat is the other important nutrient that turns to fuel, but your body can’t properly use fat without glucose present.
  • Glucose is the number one fuel for your brain almost all of the time. The brain detects when glucose levels in the blood drop, and you experience it as confusion, disorientation and fatigue — hello, bonking! Having enough glucose on board can prevent you from hitting the dreaded “wall.”
  • You have a limitless capacity to store fat, but not glucose. Your body stores glucose in the liver and in your muscles in the form of glycogen. And your body can only store enough glycogen for about 90 minutes of strenuous exercise — which explains why many runners choose to “carb load” before a race.


Eating high-carb foods leading up to a race — or “carb loading” — stocks your muscles and liver with glycogen. But it’s only necessary if you’re exercising intensely and continuously for 90 minutes or longer. (If you did it before every run, you’d likely notice your shorts getting snug.) To get the most bang from your carb-loading buck:

  • 1–3 days before a long run, ramp up your carbohydrate intake with a high-carbohydrate diet. Average runners should aim for 5–7 grams of carbohydrates per kilogram of body weight, and endurance athletes should aim for up to 10 grams of carbohydrates per kilogram of body weight.
  • 3 to 4 hours before exercising, eat a high-carbohydrate, low-fat meal, such as a turkey sandwich with lettuce and tomato, or pasta with chicken and veggies.
  • Right before the race, opt for simple carbs that are easy to digest — like white rice, pasta, pancakes, cereal, fruit bars and baked goods — to avoid stomach trouble on the road.


Taking in carbs during a run slows down the rate at which you use your stored glycogen, and helps keep you going for longer — which explains why you’ll find sports drinks and gels at aid stations for long races. When you consume carbs and protein post-exercise, you set your body up to optimally restock glycogen stores for the next run and help rebuild muscles. A few things to keep in mind when fueling on the run and after:

  • 30 minutes before exercising, have a simple carbohydrate snack, like a piece of fruit, applesauce, a handful of dried fruit or crackers.
  • During physical exertion, aim to sip 8 ounces of sports drinks every 30 minutes, or consume  1–2 sports gel packets with water every 45–60 minutes.
  • Within 30–60 minutes after exercising, have a snack or meal that combines carbohydrates and protein. Some good options: a peanut butter sandwich, chocolate milk, a banana with a serving of almonds.

Be sure to connect MapMyRun and MyFitnessPal so can you can easily track your fuel alongside the calories you burn running.

About the Author

Trinh Le, MPH, RD
Trinh Le, MPH, RD
Trinh is a registered dietitian by day, blogger at Fearless Food RD by night. She loves helping folks develop a better relationship with food, which includes lots of cooking, eating and learning about nutrition. When she’s not snapping mouthwatering shots of (mostly) healthy food, you can find Trinh HIIT-ing it at her local gym. For more, connect with her on FacebookInstagram and Pinterest.


11 responses to “Why Runners Need Carbs”

  1. Avatar diggindeep says:

    I thought carbs are bad? Boy, there is some bad information on the Forums!

    • Avatar Stephen Alami says:

      Not sure if you being sarcastic here or you genuinely think carbs are bad for you? I hope it it`s the former!

  2. Avatar Macoola says:

    Great article always been confused about this, everyone always says ‘stay away from carbs’, but this makes so much sense!

  3. Avatar nat says:

    I run first thing in the morning on an empty stomach or a banana if I do feel a bit hungry but most time I’m not. Each to there own though .

  4. Avatar Stephen Alami says:

    Agree, so much bad advice out there has caused people to be afraid of carbs assuming weight gain. It is all about calories, not carbs. Eat carbs, means a better workout generally which means increased expenditure (Kcals). I went on a low carb diet to try and get to 10% bofyfat and I just stalled. Started eating more carbs and weight fell off….

  5. Avatar Mary says:

    I don’t agree at all. While some carbs are fine yes (from nutrient rich sources), we all have different levels of needs. For me I have learned to run on a low carb high fat lifestyle and have done much better than the last time I tried on a normal diet. The standard American diet (ie high carbs like suggested here) has never worked for me. Not to say I am always perfect in my eating, and I will eat more carbs on days I’ll be running around all day photographing weddings, but it’s nowhere close to even what they suggest to eat on an average day! I wish American dieticians would catch up and realize carbs at this level are not good for everyone, in fact more benefit from low carb than high…. Yes even when running.

  6. Avatar fatburningrunner says:

    Suggest the author revisits the literature on carb loading as this article is out of date. Extensive research by Prof Tim Noakes draws very different conclusions about the role of carbohydrates in endurance sports.

  7. Avatar karl says:

    What a terrible article, out dated info. A ketogenic diet is much more efficient, you do not need carbs

  8. Avatar Stu says:

    My own (anecdotal) experience has shown my body adjusted to a reduced carb diet over several months. I’m certainly not ketogenic with a carb intake between 80-150g per day but this is still significantly less than the government recommendation and I’m able to sustain an average pace of up to 5 mins/km in my regular training, usually 10km but up to 21 on occasion and I never bonk unless I specifically plan to run til I drop. I think the trouble is in defining who really benefits from carbs. Competitive Sprinters and extreme endurance racers: sure, those are both reasonable candidates for a higher carb intake although some are very successful on low carb diets. Leisure runners and joggers: absolutely not! Anyone in between: maybe, but it’s not essential if they’re willing to make time for the adaptation.

  9. Avatar Caito says:

    Sorry but the above is misleading. Recent study with proper fat adapted athletes demonstrated the body didn’t require carbs to produce glycogen from stored fat. Yes the brain needs carbs, but not the amount suggested above. I have followed high fat low carb for 12 months and have not bonked once! I completed an Ironman using nut butter and bananas,I didn’t eat for the final 10 miles of the run as my body just kept on burning fat!!

  10. Avatar sewnaomi says:

    I have found that I cannot do my regular hills when on a very low carb diet. I can run the same on a flat course but not hills. Its like I don’t have the power/strength to tap into. I’m not an expert but just learned by failure and experimenting.

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