A Closer Look at "Types" of Carbohydrate

A few weeks ago, after writing about carbohydrates, a follower of mine on Twitter asked a question. He was interested in knowing whether simple carbohydrates should be consumed between close spaced workouts and complex carbohydrates during longer rests?

To answer this question we are going to have to take a closer look at the types of carbohydrates.

As I previously discussed, carbohydrates can be classified as simple or complex or as sugars and starches. But, they can also be classified as “quick” or “slow” in a system, I am sure many of you have heard before, the glycemic index (GI). The textbook, Practical Applications in Sports Nutrition (2 nd ed.), defines the glycemic index as “an index for classifying carbohydrate foods based on how quickly they are digested and absorbed into the bloodstream. The more quickly blood glucose rises after ingestion, the higher the glycemic index” (p. 78). Nancy Clark’s Sports Nutrition Guidebook defines the glycemic index as, “how 50 grams (200 calories) of carbohydrate (not counting fiber) in a food will affect blood sugar levels” (p. 107). To give you an example, if you were to consume a high GI food, such as white bread, it could cause a quick rise of your blood sugar, whereas, if you were to consume a low GI food, such as kidney beans, it would cause a slower increase of your blood sugar.

Many people often associate simple carbohydrates with high GI foods and complex carbohydrates with low GI foods, perhaps this is what my Twitter follower thought? (Perhaps not and I apologize if I am wrong Twitter follower ☺)
However, there are quite a few foods that do not fit this assumption. Complex foods can have a high GI and believe it or not, simple carbohydrates can have a low GI. For example, fructose, a simple carbohydrate has a low GI. And a baked potato, a complex carbohydrate has a high GI.

SO, why does any of this matter or does it not matter at all??

Originally, the glycemic index was designed and intended for people with diabetes, as a means of helping them control their blood sugar levels. The glycemic index examines foods as single food items, not combination foods, such as lasagna. Of course scientists started to become interested in the glycemic index and its potential in aiding athletic performance. There have been quite a few research studies performed. However, results are mixed and the Sports Nutrition A Practice guide for Professionals (4th ed.) states, “additional studies are warranted” (p.18).

There are pros and cons to the glycemic index. The glycemic index can be affected by many factors. And so, I personally believe there are many limitations to the GI and athletes shouldn’t get all worked up about the glycemic index.

The following are factors/limitations that can affect the GI of a food (1):
• Fiber content of a food
• Protein and Fat content of a food (can delay a rapid increase in blood glucose levels)
• Liquid versus solid form
• Timing of the meal
• Consuming a variety of foods at one time (meal) (Remember: the GI only examines a single food item, not combinations)
• Consuming more than one carbohydrate food at a time

ALSO…

“Each of us has a differing daily glycemic response that can vary approximately 43 percent on any given day” (2). AND, remember well-trained athletes’ muscles quickly use carbohydrate in the bloodstream, meaning that athletes produce LESS insulin and therefore, do not have increases in blood sugar levels, like unfit people can have (2).

Based on these limitations of the glycemic index and through my own experience, the best advice I can offer is to consume foods high in carbohydrate (they are a main source of FUEL for an athlete) that digest well, taste good, and that work best for YOU! I always tell my athletes, just as you practice for your sport, you have to practice eating for your sport! Try different types of carbohydrate before, during and after your workouts to know which ones work well for you. What works well for you, may not work well for your friends or teammates! You want to make sure that they digest well and don’t cause gastric distress. Keep in mind, the time to try a new food or drink should be around times of practice, NOT competition, you don’t want to try something new on the day of a race!

However, if you want to know what some of the research says and try it out for yourself, here is what some research recommends (Remember…more research is needed and there are NO set recommendations for athletes regarding GI)

1.) Pre-exercise meal: Low GI carbohydrate foods (theorized to provide sustained energy) (1, 3)

2.) During exercise: Moderate to High GI carbohydrate foods (For high-intensity or long endurance sports, there is a need for carbohydrate, especially if glycogen stores are low or depleted. These foods can quickly supply glucose for energy) Example: Sports Drinks. (1, 3)

3.) Post-exercise meal: Moderate to High GI carbohydrate foods (As mentioned above, these foods can quickly supply glucose for energy, but they can also replenish glycogen stores quickly) (1, 2, 3).



Going back to my Twitter followers’ question… “Should simple carbohydrates be consumed between close spaced workouts and complex carbohydrates during longer rests?”

From the glycemic index perspective and research, High GI carbohydrate foods should be consumed between close spaced workouts, again, because they provide glucose quickly and can restore glycogen quicker than low GI foods. Again, you want to consume foods that are easily digested between workouts! FYI… carbohydrates digest quicker than protein and fat! You also want to make sure you are consuming enough carbohydrate between workouts as well. The last thing you want is not having enough energy! I will talk about this topic more when I discuss pre- and post-exercise meals. But, a general guideline to follow for post-exercise carbohydrate intake is the following:

1- 1.5 grams of carbohydrate/ kilogram of body weight immediately after exercise (2, 3)
Additional 1- 1.5 g of carbohydrate/ kg 2 hours later (3)

As for carbohydrate intake during longer rests (such as 24-hours), there is some research that supports a Low GI diet. This information relates back to information from my “carbohydrate rebuttal.” For example, “the low-GI diet might facilitate better replacement of intramuscular fat stores (important for endurance) as well as enhance the use of fat for fuel, instead of the limited (and limiting) glycogen stores” (2).

In summary, carbohydrates are very important for energy and should therefore be consumed in an athletes diet everyday. How you choose what “types” of carbohydrates to consume is up to you. However, they should be easy to digest and work best for you. I can’t emphasize enough how important it is to consume carbohydrates after workout or between workouts, as well as during workouts lasting longer than 90 minutes! All types of carbohydrates are important, especially fruits, vegetables and whole grains, as all of these provide specific vitamins, minerals, fiber, and phytochemicals. If you decide to try and follow the GI index and the proposed recommendations for athletes, go for it, BUT keep in mind the limitations of the GI, the various factors that can affect the GI of foods, and that it is not easy to follow the GI.


If you are interested in more information about the glycemic index or want to check out an index of various food GI go to this website:
Home of the Glycemic Index
http://www.glycemicindex.com/

REFERENCES:

1. Hedrick Fink, H., Burgoon, L. A., & Mikesky, A. E. (2009). Practical applications in sports nutrition (2nd ed.). Sudbury, MA: Jones and Bartlett Publishers.

2. Clark, N. (2008). Nancy clark’s sports nutrition guidebook (4th ed.). Champaign, IL: Human Kinetics.

3. Dunford, M (Ed.). (2006). Sports nutrition a practice manual for professionals (4th ed.). Chicago, IL: American Dietetic Association.