Modified training diet

Related Terms

Athletic training, carbohydrates, carbs, carbo loading, depletion stage, diet, endurance training, glucose, glycogen, ketoacidosis, modified training diet, packing, super-compensation.

Background

The carbohydrate loading diet, also known as carbo loading, is a week-long eating and exercise plan, which is said to boost the performance of endurance athletes by boosting the reserves of available energy during continuous activity. The carbohydrate loading diet does not change the performance of athletes who participate in "stop and start" (non-endurance) sports such as baseball, soccer, and football. Carbohydrates are the primary source of energy from food in most American diets. Common foods that are high in carbohydrates include bread, pasta, bran, cereals, and potatoes.
The carbohydrate loading diet is a relatively new diet. Advances in the understanding of human metabolism in the last 50 years led to the theories on which the carbohydrate diet is based.
The World Health Organization recommends that people derive 55% - 75% of their body's energy from carbohydrates. The carbohydrate loading diet involves an increase in carbohydrate intake while simultaneously decreasing the consumption of fatty foods.
There is evidence that carbohydrate loading may improve sports performance by delaying fatigue on the day of the event. However, most experts advise against carbohydrate loading, except on a very occasional basis, because of the long term consequences related to altered carbohydrate intake, such as weight gain, muscle wasting, and possible development of insulin resistance and diabetes.

Theory / Evidence

Carbohydrates exist in simple (table sugar) and complex (whole grain) forms. During step two, an athlete who is carbohydrate loading consumes both forms.
Energy derived immediately after ingestion of carbohydrates is in the form of glucose. Excess glucose that is not immediately used by the body is stored in the muscles as glycogen.
Upon exertion, the body will use any available glucose for energy before attempting to use stored glycogen. Glycogen stores are typically depleted within 90 minutes of continuous activity. After this, the body must switch to other less efficient pathways to supply the muscles with adequate energy. This is usually the point when the athlete begins to experience fatigue and performance begins to decline.
Carbohydrate loading does not benefit athletes who participate in non-endurance sports, such as football, volleyball, and basketball. Athletes in non-endurance activities replenish their body's energy supply by eating during events. In addition, the rest between activity allows the body time to recover.
Advocates claim that the carbohydrate loading diet increases the ability of muscles to store glycogen. As a result, the body has more energy to burn before the onset of fatigue.
Preliminary evidence supports the theory that carbohydrate loading may boost immediate sports performance. However, most experts warn against carbohydrate loading as a long-term eating strategy for athletes. Over time, an individual may loose muscle mass, which may lower sports performance.
Overeating with the intent of carbohydrate loading may result in weight gain, even if foods are fat free. Critics claim that individuals may experience fatigue because carbohydrates usually only provide short-term energy storage.

Author information

This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography

American College of Sports Medicine. 20 June 2006.
American Council on Exercise. 20 June 2006.
Coyle EF. Carbohydrate supplementation during exercise. J Nutr. 1992 Mar;122(3 Suppl):788-95.
Coyle EF, Coggan AR, Hemmert MK, Ivy JL. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. J Appl Physiol. 1986 Jul;61(1):165-72.
Holloszy JO, Kohrt WM, Hansen PA. The regulation of carbohydrate and fat metabolism during and after exercise. Front Biosci. 1998 Sep 15;3:D1011-27.
Ivy JL, Katz AL, Cutler CL, et al. Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion. J Appl Physiol. 1988 Apr;64(4):1480-5.
Rowlands DS, Hopkins WG. Effects of high-fat and high-carbohydrate diets on metabolism and performance in cycling. Metabolism. 2002 Jun;51(6):678-90.
World Health Organization. 19 June 2006.

Diet outline

For the first three days, the athlete consumes a modified training diet, consisting of high-fat, low-carbohydrate foods (60-120g carbohydrate). This first step of the carbohydrate training diet is also called the depletion stage. On day one of the depletion stage, the athlete trains to exhaustion; such vigorous activity depletes the muscles of glycogen. During the next two days, the athlete trains moderately. The athlete must engage in the sport during this stage because carbohydrate loading only occurs in the specific muscles exercised. During the carbohydrate loading stage, the diet is switched to a high-carbohydrate intake (400-600g carbohydrate) for the next three days, while training time is reduced. This will result in muscle glycogen "packing," increasing the muscle glycogen to a new, higher level. Foods that are high in carbohydrates include brown rice, oatmeal, whole grain breads and crackers, whole grain ready-to-eat cereals like bran and shredded wheat, potatoes, pasta, macaroni, dried beans and peas, fruits and vegetables, fruit juices, ice cream, cookies, candies, and soda.
The carbohydrate loading diet is usually performed in three steps leading up to the day of the sports event.
Step one: This step usually begins six days before the planned competition. Athletes will engage in a strenuous training session, depleting glycogen stores in the body. Additionally, the athlete follows what is known as the "modified training diet," where high-fat, low carbohydrate foods are consumed. For the next two days, physical activity is continued but to a lesser extent as on day one, and the modified training diet is continued.
Step two: Beginning on day four and lasting until before the competition, the athlete begins to consume large amounts of carbohydrates and eliminates fats from the diet while further decreasing their level of physical activity.
Step three: The athlete eats a normal meal before the competition.