Despite the popularity of low-carb diets, carbohydrates are not your enemy. They're your body's primary fuel source, which is why you get tired more easily when you severely restrict your carb intake. Excess carbs will get stored as fat, but eating the correct amount will give you the energy to get through your day and power through your workout.
Carbohydrates
When you eat carbs, the carbohydrate molecules are broken down into the sugars from which they are made. When the sugars hit your small intestine, they are absorbed into the bloodstream, triggering the release of insulin. Insulin allows the sugar molecules to enter the cells, where they are converted to glycogen that is stored in the muscles and liver. Glycogen is a ready source of energy, stored for when you need it. When you exercise, your body calls upon these energy stores to fuel your movement.
Carb-Loading
Once you exercise for a while, you begin to run out of glycogen. Even if you consume carbohydrates during your workout, your body can't convert them to energy fast enough to meet the demand, so you become tired. To prevent this, many endurance athletes practice "carb-loading" before events lasting longer than 90 minutes, like marathons and bike races. About a week before the event, they severely reduce their carbohydrate intake for a couple of days so they can use up every drop of glycogen they have stored. Then for the final three or four days before the event, they increase their carb intake to about 70 percent of their calories -- this allows them to fill up those empty reserves, packing glycogen away so they have large stores available for those last few miles.
Low-Carb Diets
Many dieters assume that carbs are bad because they lose weight on a low-carb diet. While weight loss does occur and can be substantial, it is only temporary and will return. Carbohydrate molecules are made of carbon atoms bonded with water molecules. For each glycogen molecule you store, you also store four molecules of water. When you stop filing your glycogen stores by restricting your carb intake, your body begins to burn your stored glycogen to fuel your daily activity. As the glycogen molecules are used, the water is released and excreted. So the dramatic weight loss in the beginning of a low-carb diet is all water weight, which will return as soon as you begin storing glycogen again.
Guidelines
Most people should get between 45 and 65 percent of their calories from carbohydrates. If you're sedentary, stay toward the bottom end of the range. If you are an endurance athlete, aim for the high end. Focus on healthy carbs like fruits, vegetables and whole grains. These foods supply fiber and vitamins as well as carbs. Avoid refined carbs like white flour and sugar, because they don't contribute much more than calories.
References
- MayoClinic.com; Healthy Diet - End the Guesswork With These Nutrition Guidelines; February 22, 2011
- Elmhurt College Virtual Chembook; Overview of Carbohydrate Metabolism; Charles Ophardt; 2003
- "Journal of the International Society of Sports Nutrition"; Gender Differences in Carbohydrate Metabolism and Carbohydrate Loading; Jennifer Wismann, Darryn Willoughby; 2006
Member Comments