Saturday, December 18, 2010

Nutrition and Racing, Part I: Carb-Loading

As you know, I'm a triathlete.
Triathlons come in a large variety of sizes; from Mini-Triathlons which may take a total of 30 minutes to complete all the way up to the Ironman which can span 17 hours for some athletes. 

Most people (in my opinion) would agree that athletes require a slightly different approach to nutrition, let it be that they simply need more calories each day, may need more electrolytes, more protein, more fruit, or whatever.  This set of blogs (I will be continuing this "series" for quite some time I'm sure) is going to explore what an "athletic diet" really is and should be.

My first question to tackle stems from being an athlete in a sport that offers both sprint and endurance races. I've been in races that have taken anywhere from 24 seconds to an hour and thirty-five minutes.  I'm also training for a race that I predict will take me twelve hours to complete.  But in the midst of all of this can I assume that athletic diet suggestions apply both for sprinters AND endurance athletes?  Specifically...
Q: Does carbohydrate-loading work equally for sprint and endurance athletes?

I grew up on the carbohydrate loading method.  The night before my swim meets, my family would always have pasta for dinner.  The goal is to saturate your body's carbohydrate stores, which serves as a primary source of energy; more stored energy on reserve means greater energy available for use come race time.  That seems quite reasonable on the surface.  Where I find this idea to break down is in the answer to the question of "how much carbohydrate can your body store?"

Carbohydrates are broken down in the body and stored as glycogen (a form of sugar; glucose) in the liver and muscles.  The vast majority (75-80%) of the glycogen is stored in your muscles and is used for muscle movement, while the liver, which is in charge of maintaining blood-glucose levels, only receives 20-25% of stored carbohydrate.  Exercise-induced hypoglycemia, or low blood sugar, causes fatiguing of muscles, dizziness, light-headedness, disorientation, along with a long list of other variable symptoms.  To various degrees, these are the symptoms of "bonking" or "hitting the wall."

Athlete on a Typical Diet
As far as I've read, it seems an athlete on a typical diet (roughly 50% of calories from carbs) can store up to 350g of carbs and only 20-25% of these are stored in the liver while the rest goes to the muscles.  Therefore, approximately 80g goes to the liver.  As far as carbohydrate usage, I've read that at a moderate workout level, the body can burn through blood glucose at a rate of 60g/h.  This means that the average athlete on a typical diet will begin to be hypoglycemic (burn through the liver's carbohydrate stores and no longer be able to regulate blood glucose levels) in an hour and twenty minutes.  Given my own experience and that of other athlete's I know, this time frame is quite accurate.

Athlete on a Carb-Loading Diet
If however, this athlete is elite and goes on a carb-loading diet, it seems approximated that they could store up to 850g of carbs; 190g to the liver.  This athlete then would last three hours and ten minutes before becoming hypoglycemic. 

From this idea alone, the carb-loading diet seems quite reasonable, wouldn't you agree?  But what happens when an athlete goes beyond their carbohydrate store?  Does that mean that they have to stop racing and refuel?  No.  Anyone who has heard of things called "bonking" or "hitting the wall: or has experience with it themselves knows that you can push through the end of your carbohydrate stores.  Ok, some more science...

Your body in general burns fat and carbohydrates in a certain individualized ratio.  For the sake of this blog, let's assume it's 50:50.  Protein is the third major energy source, but your body does not generally go to that source outside of extreme or specific conditions, so I will ignore that for the time being.  If your body burns fat and carbohydrates equally to obtain energy for general exercise, what happens when you hit the end of your stores?  It's quite simple, your body burns more fat.  

A youtube video by Tim VanOrden who runs introduced me to the idea of altering the way your body obtains energy.  What he explains in the video is how to teach your body to burn fat more efficiently than carbs.  He lowers his carbohydrate intake and goes on long runs.  What happens is he depletes his carbohydrate stores and his body switches over to burning more fat.  Over time, the idea is that your body will begin to start burning more and more fat right from the start.  Now why would you want to do this?  No, he's not trying to lose weight.  Comparatively, your body can run for DAYS on its own fat while you can only run maybe three hours at most on carbohydrates.  Therefore, if you can switch over to fat burning, you avoid hitting "the wall," you maintain your energy, and you can race for much longer periods of time.  This seems like the holy grail for endurance athletes, right?  Any endurance athlete would end up repeatedly hitting "the wall" and over time alter their body accordingly, but altering your diet in order to optimize that change seems quite useful in order to get the most of of each workout.  

Tim VanOrden began this diet because he was training for a marathon and thought it would be helpful.  Given that I am planning on running a marathon along with two half-Ironman races this coming summer, I jumped on this idea and began researching.  From what I've read, the science behind how your body switches from carbs to fat for energy is not well understood, though it is process well recognized to occur through training.  I'm planning on giving it a try come Spring.

So back to my question:  Does carbohydrate-loading work equally for sprint and endurance athletes? I have focused here on the idea of carb-loading and would conclude that it holds the most benefit for sprinters. Therefore, I would answer...
A:  No, carb-loading does not hold the same benefit for sprint and endurance athletes, though I admit that all athletes require carbohydrates for some portion of energy.  However, endurance athletes should focus more on a nutritional system that teaches their body to be increasingly efficient at burning fat. 

As I dig deeper and deeper into the details of carb-loading and various endurance athlete diets, I will add to this series of blogs.  Below are other topics I plan on covering (and the list will of course expand as time goes by). 
- Carb-Loading
- The Science of Carbohydrate Storage
- Energy: Protein vs. Carbs vs. Fat
- During-Race Nutrition
- Training versus Race-Prep Nutrition
- The Dean Karnazas Diet
- Protein Supplementation
- Raw Foods

If you have any questions or comments, please let me know!  I'm always happy to answer questions or join discussions.  Please feel free to correct me where necessary; I'm not an expert.


Chelsea said...

Very interesting! I would love to find out more about this. Is there a way to stick to a lower carb diet while you are training and avoid the negative side effects of ketosis (i.e. kidney problems etc)? I would love to avoid carbo loading for longer runs!

Kurt @ Becoming An Ironman said...

Absolutely! Tons of people eat low-carb diets as a normal diet.

First, I would suggest first looking at the labels of food you normally eat. You may be surprised how many carbs are in some foods and how many foods have alternatives with lower carbs (low sugar food tends to be low in carbs as well). Once you identify what you eat in carbs, it is much easier to know how to lower your daily intake.

To lower the carb intake in my own diet, I would lower my intake of pasta, bread, alternate some drinks for "light" varieties, and alternate some cereal for fruit or yogurt. Naturally, lowering carbs would increase my intake of fruits, veggies, and protein.

I will note though that going through the process of switching your body over to more efficient fat burning will cause much more ketosis in the beginning. It will take some time for your body to adjust and I personally can't say how long to expect that change to take. I will certainly be documenting that when I do it myself this Spring.