Carbohydrate plays an essential role in energy production. Carbohydrate is the most efficient fuel source because it requires less oxygen to burn than fat or protein. The most common dietary forms of carbohydrate are complex carbohydrates (found only in plant-based foods) and simple sugars (honey, table sugar, high fructose corn syrup). All carbohydrate sources are eventually broken down into glucose, which can be used as a fuel source or stored as muscle or liver glycogen when entering the bloodstream. if carbohydrates are consumed in excess of daily energy needs, they are converted to stored body fat.
Muscle glycogen (carbohydrate) is the primary energy source for a working muscle. each athlete has a limited capacity to store glycogen. Just like a car with its limited gas tank storage capacity, the human body can only store so much carbohydrate in both the muscles and liver. nonetheless, the body can increase its glycogen storage capacity through endurance training and a maintenance of a high carbohydrate diet, which can boost endurance performance.
Carbohydrate Performance Functions
• Fuel the brain and nervous System – Under normal health conditions, the brain uses only carbohydrate (glucose) as fuel. If the diet is inadequate in carbohydrate, blood glucose (sugar) levels can drop and the athlete may have trouble concentrating and performing basic skills.
• Preserve Protein – When the diet is inadequate in carbohydrate, the body breaks down protein and converts it to carbohydrate. Protein is a less desirable fuel source since it is needed for the growth and repair of muscle tissue. A diet with sufficient carbohydrates and calories helps spare lean muscle mass.
• Aid in fat Metabolism – even the leanest triathlete has more than enough stored fat to fuel hours of training. in order to utilize fat as a fuel store, the body does need carbohydrate to help the process. The carbohydrate stores can actually limit fat metabolism.
Daily Carbohydrate Requirements
Carbohydrate recommendations are often expressed as 45- 65% of total calories. While this may be appropriate for active individuals looking to lose weight, it is not the best practice for athletes. Carbohydrate needs can change from day to day. it is more appropriate to estimate daily carbohydrate requirements in relation to body weight (though lean mass weight is ideal) and to consider the intensity and duration of the activity. Table 6.2 outlines the base carbohydrate recommendations for a training day. Using the prior example, a 150 pound olympic-distance athlete doing a two hour combination workout may need 450- 675 grams of carbohydrate.
Athletes should be encouraged to consume complex carbohydrate food sources as the base of their daily diet. They should select whole grain breads or cereals, fresh fruits and vegetables (especially high carbohydrate potatoes, peas, beans). Athletes should also be educated on the potential benefits of some simple sugars in the diet, especially following a long or hard training session.
The Glycemic Index
The Glycemic Index (GI) is a system that classifies carbohydrate foods based on their ability to affect blood glucose (sugar) levels. It is generally better to have a slower, gradual rise in blood sugar than a sudden increase. Carbohydrate sources that enter the bloodstream quickly have a high glycemic index rating. These can be useful post-workout to aid with glycogen storage and during a workout to help maintain blood sugar levels. Carbohydrate sources that enter the bloodstream more slowly have a low glycemic rating. These may be beneficial as part of a pre-workout/ race meal or during longer training sessions for a more sustained release of blood sugar. It should be noted that the GI rating of a carbohydrate could be influenced by other nutrients. The addition of protein, fat or fiber, for instance, can lower the impact of a high-gi food.