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My cross team strongly promotes loading on carbohydrates the night before our 5k meets. I understand that carbo-loading is great before a marathon, where endurance is very important, but, with a 5k being so short, how much does carbo-loading really benefit a 5k runner?

Another point is, typically, what you eat the night before, will still be in your stomach when you race, so filling too much on carbs can have a negative consequence by adding extra weight, correct me if I'm wrong.

Large portions before a race can, however, decrease race-day performance if the digestive system has not had the time to process the food regimen. — Wikipedia (http://en.wikipedia.org/wiki/Carbohydrate_loading)

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From Iowa State University:

A well-nourished adult can store approximately 500 grams or 2000 kcal of carbohydrates. Of this, approximately 400 grams are stored as muscle glycogen, 90-110 grams as liver glycogen, and 25 grams circulate in the blood as glucose.

I don't think the weight is very relevant. Answering your question directly, the goal for carboloading is to ensure that you have sufficient glycogen for your event. Running 3.1 miles at ~6-minute-miles would take something like ~700 calories (depending heavily on a variety of factors such as your body weight, training, the terrain, etc).

So having 2,000 calories stored might be a bit overkill, but to get to that number you'd need to do depletion in advance and eat lot of lower-GI foods.

  • I would tend to agree, so I guess we could conclude that it's not as necessary for a 5k as some people I know make it, but a little carboloading won't hurt, and may reassure a good amount of glycogen. – aaronlbrink Oct 4 '14 at 12:48
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Carbo loading is generally recommended for endurance events - anything longer than 90 minutes at a moderate pace. In addition, carbo-loading typically has to be done several days in advance. It's possible to glean benefits from carbo-loading the day before, but only if you've been actively maintaining your glycogen stores by replenishing them after excercising.

Basically, a 5k run isn't long enough to use up your glycogen stores unless you're really not getting enough carbs in your diet, so the carbo-loading is kind of pointless. It also depends on the type of foods that you're using for your carbohydrates. Grains can negatively impact your performance, especially wheat glutens which create inflammation.

The general recommendation for eating before a 5k is simply to eat a good meal 3-4 hours before the event. Something with complex-carbohydrates - e.g. fruit and whole grains - not simple carbs like sugar, as this can spike your insulin levels and make you sluggish.

If you wanted to feel what it's like to run out of glycogen during a run, I'd suggest doing a 20k (or half-marathon). Without carbo-loading beforehand, you'll likely deplete your energy stores and enter a state of low blood-sugar (aka "hitting the wall") about 15km or 90 minutes into it.

Over time, endurance training increases the amount of glycogen that your body can store, so you can run longer before hitting the wall, as long as your glycogen stores are full.

  • I mean, I wouldn't think that it's completely pointless, but I would agree that it for sure will have a much stronger affect on 20ks and above. – aaronlbrink Oct 4 '14 at 12:42
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    @Aaron it's true that there's some evidence that running with a full glycogen store may improve performance, even in a relatively short event like a 5k, but unless you're doing it for a competition (not just training), it doesn't seem worth it. I run three 5k's a week personally, and I rarely notice a difference based on diet. – TonyArra Oct 4 '14 at 21:21

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