Carbohydrate loading is a strategy used by endurance athletes to enhance performance during competitions.  The goal is to maximize the body's glycogen (energy) stores to delay the onset of fatigue during an event.  This concept was introduced in the late 1960's by scientist Bengt Saltin.  To understand the premise of carbohydrate loading, an explanation of how carbohydrates are used by the body to support exercise is warranted.  Your body can break down carbohydrates more readily and efficiently than either protein or fat and, therefore, are the main fuel source for your body during strenuous prolonged exercise.  

     Carbohydrates are stored in your muscles and liver as glycogen and circulate in your blood as glucose.  Muscle glycogen is a quick source of energy for the working muscles.  Glycogen stores in the liver are released into the blood stream as glucose to assist with meeting the energy requirements of the exercise.  Glycogen stores become depleted when exercise is intense and lasts 90 minutes or more.

     The amount of stored glycogen is an important factor for optimal performance during sustained endurance exercise.  If your stores are low at the beginning of the event, you will fatigue sooner.  Carbohydrate loading, in which glycogen stores are increased beyond normal levels, can prevent this.

Who Should Carbohydrate Load?

     Individuals whose competition requires intense exercise that lasts for 90 minutes or more (e.g. marathon runners and triathlon athletes).  In general, carbohydrate loading does not provide additional benefit to individuals who participate in events of shorter duration because the body's glycogen stores are sufficient to meet energy needs during this type of activity.

Methods of Carbohydrate Loading

     The original method involves a depletion phase followed by a loading phase.  This strategy is started several days before your competition.  The depletion phase requires you to train hard for 3-4 days while consuming a low-carbohydrate diet to deplete your glycogen stores. This phase serves to stimulate glycogen synthetase, an enzyme that forms glycogen.  The loading phase involves 3-4 days of rest while consuming a high-carbohydrate diet.  This "deplete then load" regimen maximizes glycogen stores because the extra carbohydrates consumed are converted to glycogen by the elevated levels of glycogen synthetase circulating in the blood.  Unfortunately, for some individuals, this method can have side effects such as abdominal distress and water weight gain.  As a result, an alternative carbohydrate loading method has been developed.

     The modified carbohydrate loading method eliminates the depletion phase.  It involves increasing your consumption of carbohydrates while decreasing the duration and intensity level of your workouts 3-4 days before your event.  The increased amount of carbohydrates consumed should account for 65-70% of your total daily calories and come from complex sources such as whole grain pasta. 

Points to Consider Regarding Carbohydrate Loading

• Although more research is needed, the results of the few studies that are available indicate that women are less responsive to the effects of carbohydrate loading than are men.  The menstrual cycle is thought to play a role.
  
• The results of carbohydrate loading are specific to the muscles in which the glycogen stores are depleted.
  
• Individuals respond differently to changes in their diet; therefore, you should experiment with carbohydrate loading during training or before a less important competition.
  
• If the event lasts longer than 1 hour you will still need to consume a carbohydrate source such as a sports bar, gel or drink during exercise to extend performance.
• For best results, seek the advice of a sports nutritionist who can develop an individualized protocol for you to follow.

Resources:

Department of Sports Nutrition, Australian Sports Commission Website (www.ausport.gov.au) "Carbohydrate Loading," Minehan, M.

Health & Fitness Journal March/April 2008, Vol. 12 No. 2; "Fitness Focus: Carbohydrate Loading", p. 5, Thompson, D.

Fitness & Health, Sixth Edition

Mayo Clinic Website (www.mayoclinic.com) "Carbohydrate Loading Diet"