Glycogen (Carbo) Loading


Experience From - Chuck Zeugner , Jay Hodde , Rich Shick , Claude Sinclair , Jeff Selinger , Coach Weber , Karl King ,

Chuck Zeugner

Scott Burgess wrote:

Can you provide some evidence (aside from the anecdotal) for this assertion that carbo-loading is a "myth;" (i.e., that removing carbs from the diet for days 7-4 before an event and concentrating on carbs on days 3-0 before the event has no bearing on performance)?

Please note that I am not asking you to prove a negative .... merely asking you to substantiate your unsupported statement that carbo-loading is a "myth."

Diet has been shown to significantly affect glycogen storage. The routine that you mention, restricting carbs 7-4 days before the event and then going on a carbohydrate rich diet does, in fact raise levels of stored glycogen.

However, the first component of the routine, that you left out, was a glycogen depleting exercise session. the initial work was conducted in the mid '60s and reported by P. Astrand.

There are a few problems with this routine including irritability, lethargy and the possibility of injury or overtraining. For that reason, some researchers have suggested that the routine be modified by eliminating the glycogen depleting run and the low carbohydrate diet portion.

In other words, reduce training the week before competition and eat a normal meal of 55% carbohydrate. Three days before competition, reduce training to a daily warm-up and consume a carbohydrate-rich diet. For a reference see:

Sherman,W. M., Costill, D. L., Fink, W. J.,& Miller, J. M. (1981) Effects of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. International Journal of Sports Medicine.

Jay Hodde

"Diet has been shown to significantly affect glycogen storage. The routine that you mention, restricting carbs 7-4 days before the event and then going on a carbohydrate rich diet does, in fact raise levels of stored glycogen."
If you look at the study cited, Sherman WM, et. al., Int J Sports Med 1981;2:114 You see this:

  1. Three days of 15% CHO followed by 3 days of 70% CHO increased muscle glycogen by 207%

  2. Three days of 50% CHO followed by 3 days of 70% CHO increased muscle glycogen by 203%

  3. Six days of 50% CHO increased muscle glycogen by 159%

It is also significant that conditions 1 & 2 above caused greater glycogen to be utilized during the test run (21k) than the 3rd condition. BUT, the authors said there was no difference in the run times between groups, and the post-exercise glycogen levels between groups were similar.

What does this mean? "Carbo loading" may increase glycogen stores, which translates to greater glycogen utilization during the run. However, this doesn't benefit performance.

What is most interesting to me is that the low-CHO diet for the first 3 days had virtually no benefit over a moderate-CHO diet (in terms of glycogen storage).

This could be the study that Rich was referring to when he talked about the "myth" of carbo-loading. It has been generally accepted that the "depletion" phase of 1970's-sytle carboloading is of no greater benefit than eating a moderately high CHO diet and pushing additional carbs in the 72 hours preceding depleting exercise.

SO, then, Chuck's assertion that "restricting carbs 7-4 days before the event and then going on a carbohydrate rich diet does, in fact raise levels of storged glycogen" doesn't really hold. What *does* seem to be implied is that *increasing* your CHO intake in the 72 hours prior to exercise raises levels of stored glycogen.

I guess the question to ask is "What is carbohydrate restriction?"

For most American diets anyway, 55% CHO is not a restriction and is quite typical.

Rich Shick

Concur fully with Chuck Z, my post acknowledged a "normal" high carbohydrate diet and postulated that shifting to a relatively high protein diet (remember my baked potato and the bread with the peanut butter) would be unlikely to significantly impair glycogen stores. In a person who has significant gut problems this should more than offset any benefit derived by a few more grams of carbohydrate.

Claude Sinclair

When I started running I read every book that I could get my hands on about running, diet, etc. For my first two marathons I did the depletion thing and started the carbo loading during mid-week. I ran a 3:30 and 3:29 respectfully. The depletion phase made me feel weak and sick. During my next few marathons I just skipped the depletion phase and shifted to a higher percentage of carbo's during the last three days prior to the marathon. Results were a 3:17 and 2:56. For ultra runners I think the key to success is long runs and making the body adapt to using fat as energy. If we had to rely on carbo's to finish an ultra then we would not finish.

Jeff Selinger

I assume that, in the study, the caloric intake is fixed.

Would a higher calorie intake (say a steak and baked potato, ...and maybe some dessert) also increase the stored glycogen ? Or is it truly necessary to have a high percentage of carbs ?

Coach Weber

An additional point is that someone who is not fit will not benefit from carbo-loading whether he or she takes the old school approach of depletion followed by loading, or the new school approach of precision tapering concurrent with high carbohydrate intake. This is because the primary stimulus for glycogen synthesis is endurance training. All the loading in the world for the unfit (no one on this list of course) will do nothing except "load them".

The elite endurance athlete in day-to-day life typically has twice the muscle glycogen levels as that of the most expertly 'loaded' average athlete.

I can note that Charl Mattheus, in his pre-Comrades loading, favors huge bags of marshmallows and the South African equivalent of "gummy bears". Very high tech!! What works, works!

Karl King

Scott Wrote:

"One of my favorite quotes...don't remember where it came something to the effect that if you want to make sure you run the worst race of your life, make sure that you go to the traditional pre-race spaghetti dinner and load up!"
My observation is that people eat way too much pasta, as if they need to stuff in all the calories for the run before it starts. It takes a lot of water to process carbos such as pasta, but many I see will have coffee, soda or beer with their pasta. All of those tend to dehydrate the body because of the caffeine or alcohol content. So, just when the body needs a lot of water, there isn't enough. The carbs are poorly digested, resulting in bowel problems during the run, and the runner may go to the start line in a state of dehydration.

Another mistake is to eat foods that are raw or lightly cooked. Salads and fish can wreak havoc if eaten the day before the race. The salad may not be clean, and the fish may not be fully cooked throughout.

What works for me is to avoid stuffing the night before. A modest meal with easily digested carbs, and some fat usually works well. I'll wash it down with a cup of decaf and a lot of water.

You can find a lot of variation in what works, so there is no magic bullet. Some runners get good results from a lot of carbohydrate drink on the day before.