Recently, there has been a resurgence lately of low carbohydrate, high fat/protein diets in the media. The Atkins diet, the Carbohydrate Addicts Diet, and The Zone are just a few of the many diets that warn about the dangers of a high carbohydrate diet. Many active people, who have been told to follow a high carbohydrate diet, wonder if they have been led astray. To decide what diet is best for active people, it helps to look at fuel (i.e., calorie) usage during exercise.

Fuel Use and Exercise
Fuel is provided to the body in the form of calories, which come from carbohydrates, proteins, and fats. After you eat, food is digested, or broken down to carbohydrates, proteins, and fat by the body and used for a variety of purposes. Carbohydrates are used primarily as fuel, especially for the brain and muscles, while fat is used to fuel other body parts. Protein is used to build and repair muscle and other tissues. Your immune system, enzymes, and other important body components are comprised of protein. Protein is not used to fuel the body unless there is a deficiency of carbohydrate.

The body stores a certain amount of carbohydrate and fats to use for fuel after a meal. Carbohydrates are stored in the muscle and the liver as glycogen. Once these stores are filled up, excess carbohydrates are converted to fat and stored as such. Excess protein is also converted and stored as fat. Fat doesn’t have to be converted - it just stores as fat after the body uses what it needs.

Throughout the day, we are constantly burning a mixture of fat and carbohydrate. At rest, fat is the substrate of choice for the body. When you begin to run or do other aerobic exercise, the body shifts from using primarily fat to using primarily carbohydrate. In the first few minutes of exercise, the body does not have enough oxygen flowing to the muscles yet, and the body must make energy without oxygen. This “anaerobic” metabolism uses carbohydrate to produce energy for the body to use for exercise. As oxygen flow to the muscles increases, aerobic metabolism takes over. Aerobic metabolism uses carbohydrate and fat to fuel exercise (as stated above, protein is used only if carbohydrates are depleted). To continue to exercise, the body must have both carbohydrate and fat available - the body cannot burn fat without carbohydrate. The average person has enough fat stored to run hundreds of miles. However, the body’s stores of carbohydrate, in the form of liver and muscle glycogen, are limited. The amount of glycogen stored in the body is dependent on many factors (which I’ll discuss in the next article). On average, the body has enough carbohydrate/glycogen stored to last about 90-120 minutes. The carbohydrate stores are the limiting factor for endurance exercise.

Focus on Carbohydrate
So what diet is best for runners and other active people? Since carbohydrate stores are the limiting factor for aerobic exercise, a high carbohydrate diet is ideal for those interested in keeping the body fueled for exercise. Eating a high carbohydrate diet does not mean eating only carbohydrates. I have talked to a number of people who give up all their protein and most of their fat and eat exclusively carbohydrates. This is not the concept of a high carbohydrate diet. To be healthy, all diets must have a balance of calories. The general recommendation is to obtain about 55-60% of your calories from carbohydrate, 12-20% from protein, and the remainder from fat. Use protein to complement a meal, rather than using it as the main focus, but don’t skip the chicken, fish, and milk for more pasta or bagel. Balance, variety, and moderation are the keys to keeping healthy and fueling exercise.

Peggy Pletcher is a registered dietitian with a Master’s degree in exercise physiology. She is a certified personal trainer and a certified diabetes educator.

DO YOU HAVE QUESTIONS ABOUT OTHER SPORTS NUTRITION TOPICS? Click here/e-mail Peggy at pegpletch@mindspring.com to submit your ideas for future articles.

Click here & tell your friends about this page !

Have you got a human interest story about a runner you know or a race report to share ? ontherunevents.com is happy to share stories with our readers. Send us your stories, your experiences!

Copyright © 1999 ontherunevents.com, All rights reserved.
Commercial use or redistribution in any form, printed or electronic, is prohibited.