Craftsbury Marathon Nutrition Tips: To Carbo-Load or Not to Carbo-Load?

This is a repost of a blog that we published last year, that explores the concept of carbo-loading. However, with the Marathon coming up, it is certainly still a pertinent topic, and we hope racers find it useful in their personal Marathon preparation.

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From Olympic Rower and Nutritionist Carlie Geer
Inevitably the prospect of a marathon event brings up this question. The answer is, if done “properly”, carb loading can result in a 2-3% improvement in performance. This means that for a ~3 hour event you could improve you time by as much as 3-5 minutes!
The goal with carb loading is to make sure your glycogen stores (energy stored in both the liver and muscles) are maximized. This is important because glycogen is the body’s preferred fuel for moderate to intense endurance exercise. The more glycogen you have stored, the less you will need to rely on exogenous carbohydrates (“feeds”) during the event to keep your blood sugar levels up and maintain your race pace. Even with carb loading, the amount of glycogen you can store will not be enough to get you to the finish line feeling strong if the event lasts longer than ~90 minutes, so even if you do a great job carb loading you will also want to have a tried and true plan for carbo feeds (energy drink, gels or bars can all work) every 30-40 minutes after the first 60-75 minutes.


So how to carbo load “properly”? Carb loading has gone through various phases and lots of studying since its inception in the 1960s. The current recommendations involve not just increasing the amount of carbohydrate(CHO) in your diet for 2-3 days prior to the event, but also, and this is important, cutting way back on your training volume and intensity for those 2-3 days leading up to the event.
While a typical daily training diet might contain 300-500 gm CHO per day (or 50-55% of your daily calories)– depending on your gender, weight and energy expenditure, for CHO loading you will need to increase to more like 400-700 gm CHO per day (7-10 g/kg body weight).
When adding extra CHO, it is important to keep the following in mind:

  1. Avoid too many high fiber CHO’s (legumes, whole grains, fruit) in order to avoid the GI distress associated with a sudden increase of fiber.
  2. Try to decrease your fat intake some, so that your overall calorie intake is not excessive.
  3. Expect a 2-4 pound weight gain because water is stored with glycogen. This is a temporary weight gain.
  4. Just gorging on pasta the night before the race (without the recommended exercise taper and increased CHO intake over several days) will not get the kind of benefits you are looking for. In addition, overeating the night before will likely mean you will wake up feeling too full and sluggish to eat a good high CHO meal and hydrate the morning of the race, both of which are important.

Suggested ways to add CHO (without too much extra fiber):

  • Be liberal with syrup on pancakes/waffles or yogurt, and be liberal with jam on toast or pb/jelly sandwiches.
  • Eat sweetened/fruit added yogurts instead of plain yogurt
  • Increase your portion of CHO at each meal (more of the oatmeal/cereal, bread, rice or other grains, potatoes, pasta).
  • Add a glass of fruit juice if you don’t usually drink juice
  • Snack on CHOs like a baked sweet potato, a banana, pretzels or crackers.

Lastly, don’t forget to plan ahead for those CHO “feeds” during the race. Stick by the rule “never try something new on race day”!

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3 Responses to Craftsbury Marathon Nutrition Tips: To Carbo-Load or Not to Carbo-Load?

  1. Tracey McCowen says:

    Wondering if anyone is looking at being ‘fat adapted’ rather than carb loading

    • Liz Guiney says:

      Tracey- this is from author of this post, nutritionist Carlie Geer. Hopefully it helps with your question:
      “It is still early in research on this topic, and like all nutrition/athletic performance related studies, often the implications of the results must be individualized to each person’s individual physiology and performance goals.
      I would recommend the reader check out the article in Runner’s World (January 5, 2017) which sites research done in Australia and published in Journal of Physiology (volume 595, issue #9, May 1 2017). My sense is that more longer and larger studies are needed, but for now it seems the increased reliance on fat after fat adaptation may not correspond to improved performance due to the lower O2 utilization efficiency.”

  2. Laurence Wagner says:

    The concept of carb loading cam from a 1968 Scandinavian study that advocated an 80% complex carb diet, that boosted endurance by over 150% (a tripling of endurance). The study is still in modern exercise physiology textbooks, such as McArdle and Katch’s 2001 Energy, Nutrition, and Human Performance. I have a copy of this textbook.

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