The Truth about Carbo-Loading (hint: you’re probably not doing it enough)

If you follow a Paleo diet, get ready to throw it out the window.

The simple reality of running a good marathon is that you need to consume an incredible amount of carbohydrates in the days before your race to adequately fuel your muscles.

Everyone has heard of carbo-loading for long races but there are a few misconceptions. Let’s look at the popular carbo loading protocol and the actual reality of what happens to your body.

Myth: You have to deplete your glycogen stores first by consuming only fat and protein and doing 2-3 “bonk runs” to burn through any leftover carbs in your body. Then you aggressively carbo-load for a week to supercharge your body’s glycogen (sugar) supply.

Reality: The stress of carb depletion includes eating no carbs whatsoever and running on empty – essentially without fuel in a semi-fasted state. Common problems include an increased risk of injury and sickness during this period. Plus, it’s not as effective as other strategies.

Most runners are rightfully afraid of depleting their carb supply before their race and simply avoid this protocol. Instead, they focus on eating more carbs in the few days before their marathon.

The good news is that they’re on the right track! The best way to max out your muscle and liver glycogen stores is to consume a lot of carbohydrates during the 2-3 days before your race. However, most runners don’t carbo-load enough.

Researchers from Britain recently followed over 250 runners who ran the London Marathon. They found that only a tiny fraction of them consumed enough carbohydrates before the race – and those that did ran an average of 13% faster.

The new guidelines for carbo-loading call for you to consume 7-10 grams of carbohydrate for every kilogram (or 2.2 pounds) of body weight. This is anenormous number of carbohydrates; you’ll likely feel swings of energy as your blood sugar goes up and down.

How to Eat All These Carbs

But the research – and real world results – prove that it’s vital to max out your carb stores if you want to race at your potential. If you don’t, you’ll likely “hit the wall” at the common 20-22 mile mark of the race. This is exactly what happened to Jason at the 2008 New York City Marathon. He went from running 6:05 pace to 7:00 minute during the final miles.

Fast forward three years later to the 2011 Philadelphia Marathon. Jason ate more carbs than he thought was required in the two days before the race. He also ate over 160g of carbs during the race (gels and sports drink) – or the equivalent amount of sugar as a pint of Ben & Jerry’s ice cream.

Unlike New York City, Jason only slowed down a few seconds per mile in the final 10k of his 2:39 marathon. His slowest mile was 6:15 and he averaged 6:05 overall. In addition to a great marathon training cycle (obviously!), he credits his fueling strategy as integral to his performance in the last miles of the Philly Marathon.

So how do you carbo load this much? It can be daunting; 7g of carbs per kilogram of body weight for a 150 pound runner amounts to 477 grams of carbohydrates per day. There are some good strategies to make this more achievable:

  • Include carbs in every meal. The best options include oatmeal (get the sugary kind!), white/brown rice, quinoa, bread, and pizza (limit the grease)
  • Snack often: fruit is the healthy option, but you can include other questionable carb sources like chips, granola bars, cookies, candy, etc. Treat yourself – but remember it’s a snack not a meal.
  • You won’t be able to get enough carbs if you’re not also drinking carbs. Get a 32 ounce sports drink, enjoy a few glasses of juice, and add sugar to your coffee. Jason bought a 32 ounce bottle of very sweet lemonade the day before that had 120 grams of carbs.
  • The day of a race, eat a medium sized breakfast at least 2-3 hours before the start. Jason ate sugary oatmeal, a granola bar, and a banana. You can also eat toast with jelly or any combination here, but make sure you get at least 100 grams before the race. Remember, you just slept and fasted for an entire night.

Follow these carbo loading strategies before your marathon and you’ll perform better than if you didn’t. And remember that only 12% of runners in the study mentioned here ate enough carbs before the London Marathon – so most likely you’re not either.

25 Responses to The Truth about Carbo-Loading (hint: you’re probably not doing it enough)
  1. Leo

    I wish I knew this before my first marathon last November. Now I know, thanks for the tip! I’ll be ready next time November.

  2. Bill

    I generally agree with what you’ve stated here, but what about teaching your body to burn fat by doing long runs without carbo-loading. Then carbo-load in the days before the race. I ran several marathons without hitting the wall, using this plan. Your thoughts?

    • Hey Bill,

      Doing some fasted runs definitely have their place in a marathon training plan. It’s a more advanced strategy, and should probably only be done during the earlier weeks. Once you’re doing 20+ mile runs with some marathon pace running, it’s more important to optimize your pacing than your fat burning. A hybrid approach is best.

    • admin

      I’m a big believer that you can get your body to eventually burn more fat, but for me it came without deliberately training to do so. Overtime, I just started requiring slightly less to eat and drink during runs, as I think happens to a lot of people.

      But like you said, Bill, even once you are to the point of burning a lot of fat for fuel versus carbohydrate, you still want to carbo-load before the to store every bit of fuel you can.

  3. Roland

    Should I be carb stuffing myself like this before long runs as well, to see how I respond, and to potentially get more out of my long runs?? Or just pre-race?

    • You can ease back on the fueling during the earlier part of your running, but once your runs get very long and specific (like the workouts in the RYBQ plans), carb-loading is a good idea. You want to maximize performance at those times and LR’s are the most important run of the week.

  4. Daniel

    I recently attempted to run the So Cal Ragnar Relay with an ultra team of 5 people; most ultra teams had 6 people. I did not measure out my carb intake but I did start upping my carb intake starting on Tuesday (race started on Friday mid morning). By Thursday evening I was only eating carbs. I had no signs of a decline in energy at all while out on the course, I felt really, really solid over the whole event. I ran about 35 miles of my 42 scheduled miles. I consumed about 2000 calories (if that many, in food) over the course of the 28-30 hours we were on the course. I believe I expended about 7500+ calories, and I don’t think I was ever “hungry” per say.

    I am a slightly overweight runner (5’10” and 173lbs) and I have been training for triathlon for the last year now. I really think I have started to train my body to rely on fat stores for energy as opposed to carbs.

    I highly recommend everyone experience the joys and emotions of a Ragnar event.

  5. […] to eat so few carbs and still be able to crush workouts and do our long runs – intelligent carb-loading is important. That’s why I like the Paleo Diet for Athletes book I mentioned […]

  6. Nicole

    This article couldnt have been posted at a more perfect time. I have a marathon in a few weeks (first marathon as a “no meat athlete”) and my last marathon (my first) I totally hit the wall at mile 22. Hopefully, I will adequately carb load this time so it doesnt happen again!

  7. This is great information. Here is my question: My first 1/2 marathon is in 9 days… Before June of last year, I never ran 5 minutes in my life, so I am brand new to this world. Would it be helpful for me to card-load in this fashion, but only half as much since I will be running half as far as a full marathon? Thoughts?


    • Daniel

      I personally believe you should carb load according to the recommendations of the article. You really want your body to be as topped off as possible on carbs. I would not worry so much about have “too many” carbs in your system because you will have an increased metabolism and you will be burning them the rest of the day.

      You will not believe how much of a difference this will make in your running.

      Let us know how your half goes. I have my next half on 5/20, I am trying to PR with a sub 1:50 and I am going to be following these ideals.

      • Thanks, Daniel! That’s helpful! I will let you know how it goes… 1:50?! My “goal” is just to cross the finish line!

  8. jamii

    This info is fantastic. I found it thru NoMeatAthlete on Facebook.

    Thanks again! (-8

  9. mjwellman

    Great article. I also found another one that has a carb caluculator at . I missed my BQ time in three marathons by five mins because I started to fade at mile 22-23. I thought it was muscular endurance, now I’m thinking glycogen depletion. This last weekend I ran 20 miles. The day before I realized that I my training runs should be no different than my race day. With only 24 hours I carb loaded all day. By the end of the day I couldn’t eat any more. On my run on Sunday not only did I hold my pace, but the last 5 miles I was able to run at my MGP. I couldn’t do that two weeks ago. In fact, I lost time on the last 5 miles. I am convinced now.

  10. […] runner knows that carbohydrates provide the best fuel for running and that most runners don’t carbo-load for the marathon […]

  11. Carolina R.

    Should we be aiming for a certain amount of protein grams per day during these days?

    • mjwellman

      Protein plays no role in providing energy for the body during endurance activity. What I’ve read is that a little protein/fat is fine before the race, but the bulk of your intake needs to be carbs.

  12. Carolina R.

    One other question. I’m training for a 70.3 half ironman and anticipate being out there about 7 hours. Are the carbo-loading rules different based on the duration of the event?

    • mjwellman

      Good question. Being a triathlete I wondered the same thing after reading the article. I did New Orleans 70.3 last month. Mi put more emphasis on carb loading the day before. On Sunday I had one of the best races and for the first time I was able to run at a good pace (8:15) and finish without walking. Unfortunately I didn’t keep track of amount of carbs I took in (which I will do next time), but I think it was the reason I did so well.

    • Daniel

      In my opinion you will want to carb load with more complex carbs the longer the distance. I am doing the Vineman 70.3 and the SuperFrog 70.3 this year prepping for my first Ironman. I will be starting my carb loading 4-5 days pre race focusing on complex carbs. The day before race day I will greatly reduce the fiber and protein intake as they both really wreck havoc on MY system.

      I would recommend trying out the diet on a simulated racing weekend to see how you feel. I think you will be surprised.

  13. […] breakfast as you normally do before a long run (you may want to eat a few more carbs to continue carbo-loading; marathons require a lot of energy from carbohydrates, so do your best to have a carb-rich […]

  14. […] to fill up on foods that are 90% junk starch and be 100% prepared and carb loaded for your race. Carbs need to come from complex sources, such as whole grains and pastas. Snack foods should include […]

  15. harry

    i will give it a shot

  16. […] If you want to carbo-load like a pro, check out this article on how to run your fastest marathon.  […]

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