In recent years there has been a lot of hype in the media about low carbohydrate diets, such as the Atkins diet, as well as negative messages about carbohydrates. It is no wonder that many people are very confused about carbohydrates. Before we begin, what do you think about carbohydrates? What do you know about carbohydrates? Do you know what foods contain carbohydrates?
Similar to the protein entry, I would like to clear up any carbohydrate confusion, dispel myths, and have you thinking positively about carbohydrates by the time we are done.
If you read my entry about protein, you should at least know that carbohydrates are very important for athletes! This is because carbohydrates are the MAIN source of FUEL for your muscles! Especially if you take part in any anaerobic, high intensity sport or exercise (ex. sprinting), as well as endurance exercise (>60 minutes), these types of activity rely primarily on carbohydrates for energy. Whereas, low intensity exercise, such as walking, uses fat for energy.
Carbohydrate 101… again, like protein, we need to learn some basic information about carbohydrates to understand how and why carbohydrates are important for athletes.
What are carbohydrates??
Sure you are probably thinking of examples of food sources such as, bread, cereal, pasta and sugar, but let’s get specific because not all carbohydrates are the same. In the chemistry world, carbohydrates contain a “carbon backbone with attached oxygen and hydrogen molecules” (1). You are probably thinking, “I don’t care, borrrrring!” But this gives you a bit of a clue as to why carbohydrates are named carbo- (carbon) hydrates (H20)! Anyway, carbohydrates can be broken down into 2 groups or families, which are simple and complex. I’m sure you have heard carbohydrates called one of these two groups. But, do you know what they mean? Like its’ name, simple carbohydrates are simple in their structure. Meaning they only have 1 or 2 sugar molecules. In the nutrition world, they are called monosaccharides and disaccharides (mono= 1, di= 2, saccharide= sugar) (1, 2). Examples of monosaccharides include, glucose, fructose, and galactose and examples of disaccharides are, sucrose (table sugar), lactose (milk sugar), and maltose (1, 2). Disaccharides have 2 monosaccharides attached, for example sucrose is a combination of both glucose and fructose. Like the analogy I gave to amino acids, think of monosaccharides as single pieces of Lego. If you connect two or more of these simple carbohydrates together you get a complex carbohydrate. Examples of complex carbohydrates are starches (grains, legumes, potatoes) and fiber. Whether you consume a simple or complex carbohydrate, it eventually gets broken down into exclusively glucose. Even if it’s a mono or disaccharide, it breaks down into glucose (2). Glucose is extremely important because it travels through the blood as blood glucose and provides energy to cells (1, 2). Have you ever participated in a fast or skipped a meal? Were you able to think clearly? Probably not too well and that’s because the brain relies exclusively on glucose for energy!
How does the body use carbohydrate for fuel?
After eating a carbohydrate rich food, your body breaks it down into the simplest molecule, glucose (monosaccharide). Glucose is then used for immediate energy (blood glucose) and the extra glucose gets stored away as GLYCOGEN. Remember… a molecule of glucose is like a single Lego piece and so, if you connect multiple pieces of glucose you make glycogen. Therefore, glycogen can be classified as a complex carbohydrate, since its’ structure is similar to that of starches and fiber. Glycogen is stored in your muscles and liver and is easily available to be used for energy during exercise (1, 2). You may be wondering, how large are these glycogen stores in the muscle and liver? They are not very large stores and can be easily depleted after an intense workout. This is why it is important to consume foods high in carbohydrate everyday in order to ensure sufficient energy for daily practices and competition (3). The amount of stored glycogen varies person to person, but muscles contain the largest amount of glycogen (about 300-400g or 1200-1600 kcal), then the liver (about 75-100g or 300-400 kcal) and finally blood glucose (25g or 100 kcal) (3). Did you know that a well-trained muscle can store much more glycogen than an untrained muscle (2, 3)?! It’s true! Elite endurance athletes’ glycogen stores will be much greater than occasional exercisers’ glycogen stores. Pretty cool how our bodies can adapt, isn’t it?!
Hitting the Wall…
Remember in my entry about the importance of nutrition, when I mentioned distance runners “hitting the wall?’ Well, it relates to muscle glycogen stores and endurance athletes. It occurs when athletes’ muscle glycogen stores become depleted (depending on intensity of activity, usually after 60-90 minutes), the athlete begins to feel tired, fatigued, and the brain tells the athlete to stop (2). Remember the term “bonking?” This relates to liver glycogen stores. Liver glycogen stores are responsible for maintaining blood glucose levels, which, remember, the brain uses glucose exclusively for energy (2, 3). Picture this, an athlete is racing in the morning and they choose to skip breakfast or eating anything before their race (their liver glycogen stores are low, especially after a night of sleeping). How do you think this athlete will feel? Chances are they will feel light-headed, weak, and unable to think clearly. There are ways to overcome these situations, such as eating adequate carbohydrate before exercise, during exercise, and replacing what’s been lost after exercise.
Demands of Daily Training…
If an athlete trains hard everyday and consumes a low carbohydrate diet daily, this athlete will feel constantly fatigued, particularly by the end of the week. There is scientific evidence that if an athlete consumes a diet low in carbohydrate for consecutive days (ex. 3 days or more) this athletes’ muscle glycogen levels will become increasingly depleted each day (2, 3). Again, this is why it is extremely important that athletes consume a diet rich in carbohydrates daily and consume carbohydrate after a workout!
How much carbohydrate should I be consuming??
Recommended DAILY Carbohydrate Intake:
- In general for athletes carbohydrate recommendation ranges from 6- 10 grams/kilogram/day OR 55-65% of your daily calories should come from carbohydrates
- General training needs- 5- 7 grams/kg/day
- Endurance athletes (>60minutes)- 7- 10 grams/kg/day
- Ultra endurance athletes- >11 grams/kg/day
Recommendations taken from Dunford, M (Ed.). (2006). Sports nutrition a practice manual for professionals (4th ed.). Chicago, IL: American Dietetic Association.
Let’s do an EXAMPLE to help you understand, I will use myself…
I am an endurance athlete (7-10g/kg/day); I weigh 125 lb (125 lb/ 2.2lb/kg = 57 kg)
7-10g/kg/day X 57 kg = 399-570 grams of Carbohydrate per day
How many calories is that??
1 gram of carbohydrate = 4 kcal
399-570 grams X 4 kcal/g = 1596-2280 kcal of carbohydrate
I would consume the lower end of this range, 400g of carbohydrate, since my overall calorie needs are not very high and my mileage is not very high either.
FYI
1 gram of carbohydrate = 4 kcal
1 gram of protein = 4 kcal
1 gram of fat = 9 kcal
1 gram of alcohol = 7 kcal
*I will go over carbohydrate recommendations before, during, and after exercise, as well as carbohydrate loading in another entry*
SOURCES of Carbohydrate-
Fruits, Vegetables, Grains (rice), Pasta, Starches (potatoes), Legumes (beans) Breads, Cereals, Dairy Products.
In SUMMARY…
Whether you participate in intense sports, such as basketball, football, hockey, soccer, or compete in endurance sports, such as cycling, running, or swimming, carbohydrate is a primary source for fueling your body! Consuming a diet low in carbohydrate can impair your athletic performance, and who wants that? As you have learned about glycogen storage, hopefully you understand why it is important to consume a diet high in carbohydrate daily, as well as the importance to consuming carbohydrates before, during and after exercise!
For more information, check out:
“Do high carbohydrate diets improve exercise performance?”
http://www.gssiweb.com/Article_Detail.aspx?articleid=900
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.
". . . habituation to a high-fat diet returns endurance performance to normal after a few days on this diet and allows equivalent performance to that achieved on a higher carbohydrate diet" "As a result , the rate of muscle glycogen used is decreased. Most importantly, the increased ability to derive energy from fats may allow the fat-adapted athlete to continue exercising for longer at exercise intensities of 70% VO2max or less when muscle glycogen stores are at levels that would terminate exercise in the carbohydrate-adapted athlete" taken from page 140 Lore of Running by Tim Noakes MD.
ReplyDeleteWhile I agree that carbohydrates are the fastest and most direct form of energy available to an athlete, high carbohydrate diets are not the only option and some benefit may even come from low carbohydrate diets such as
Atkins or the Paleo diet
If I may impose my opinion - I am all for the Paleo diet (not the Atkins diet because I feel it carries with it a certain "weight loss" suggestion whereas Paleo is more of a lifestyle). Paleo is just what it claims to be, a diet for paleolithic man. Even the most intense, non professional athletes cannot claim to compete with the daily activities of ancient man, therefore I believe the paleo diet needs to be altered (if only slightly) to fit the realistic lifestyle of modern man. As Nicole suggested carbs are in fact a major player in the metabolism of MOST people and should not be neglected in MOST daily instances. Unless you are in the small minority of people for whom fat diets increase athletic ability you should add some carbs to your menu.
ReplyDelete