|Friday, October 29
Muscles need carbohydrates
Carbohydrates are the main, preferred source of energy for the body; they are critical nutrients for the athlete who has high-energy demands during physical activity. Stamina, power and endurance are dependent on adequate carbohydrates in the diet. Foods high in carbohydrates include complex starches such as cereals, grains, rice, bread, legumes, oats, vegetables, and simple sugars such as fruits, fruit juices, milk and sweets.
Carbohydrates are stored in the body in limited amounts. This is why carbohydrate-containing foods should be about 60 percent of the daily diet. For example, when you eat pasta the starch is quickly converted into the simple sugar, glucose, which circulates in your blood either to provide immediate energy to every cell, or to be stored by the liver and muscles as glycogen, for later use. As you move, the stored glycogen in the muscle is ready to be burned as fuel. Your muscles have about three hours of muscle glycogen stored as fuel, and your liver keeps a limited reserve of glycogen to maintain blood glucose levels between meals and while you sleep. If carbohydrate stores are not maintained through an adequate diet, glycogen stores will be depleted, and athletic performance will suffer. A clear example is the marathon runner who "hits the wall": he can barely lift his legs and cannot think clearly. This long, intensive exercise session has depleted his glycogen, causing fatigue and poor performance. Sports drinks containing glucose are designed to give a marathon runner a competitive edge.
Studies show that carbohydrates are the best fuel for your muscles. One classic study put athletes on a low-carbohydrate diet, and they performed two-hour workouts three days in a row. By the third day, they had used up almost all their glycogen and were fatigued. This is called glycogen depletion. On a high-carbohydrate diet, the replenished muscle glycogen made it possible for the athletes to perform at a high level three days in a row. Garvey, the soccer player, was running out of carbohydrate stores to fuel his muscles and as a result he became fatigued.
Carbohydrates enhance performance
The fastest muscle glycogen replacement occurs within the first two hours after exercise. What athletes eat to recover after a hard workout is critical to their continued performance. The muscles "stock up" on glycogen for the next exercise session. For this reason, it is advantageous to eat and drink high-carbohydrate foods or drinks soon after exercise.
Training regularly increases the amount of glycogen that athletes can store in their muscles. Trained athletes may have more than twice the amount of glycogen in their muscles than sedentary people, which gives them more endurance. Increasing the amount of glycogen your muscle tissues store is part of getting in shape. A well-nourished athlete can perform longer and harder at the end of a season than at the beginning.
Some runners use the technique "carbohydrate-loading" to try to gain a competitive edge for a long race. Using this technique, runners first exercise intensely without restricting carbohydrates, then gradually cut back on pre-competition training the week before, eat a high carbohydrate diet, and allow the muscle to load up on carbohydrates.
When a person begins to exercise for the first 20 minutes or so, one fifth of the body's total glycogen stores is quickly used. The muscles increase their uptake of glycogen from the liver to meet the demand. After 20 minutes, glycogen use slows down and the body begins to use more fat as a fuel. Glucose must be present for fats to be burned for energy, so carbohydrates are the limiting factor in this metabolism. Untrained muscles use more glycogen faster than muscles of a trained athlete.
When you need energy for exercise, your body will use a mixture of glycogen (carbohydrate) and fat as fuel. The higher the intensity of the exercise, the more glycogen used. Sports such as tennis or sprinting require muscle glycogen as the main fuel. Endurance exercises such as jogging, bicycling or swimming first use some glycogen and then rely on more fat stores as fuel.
How to get carbohydrates
What kind of carbohydrates are the best - those we get from soda or the ones in pasta? Muscles store sugars and starches (which are converted to sugar) equally as glycogen. However, the complex carbohydrates are quite nutritious, offering B vitamins and iron and fiber for assistance in all body functions. Fruits, vegetables and legumes also offer antioxidant benefits. Simple sugars, soda and sweets, will supply plenty of easy-to-eat carbohydrates, but not much nutritional value. Fruits and dairy products offer simple sugars in the form of fructose and lactose, but mediums containing these simple sugars provide much more than just calories. Orange juice and soda contain about the same amount of carbohydrate calories, but the orange juice gives you twice the RDA for Vitamin C, plus the potassium to replace what you lose from sweating. Dairy products offer calcium, potassium and protein.
How much carbohydrate should an athlete consume? The target sports diet is 60 percent carbohydrate, 15 percent protein, and 25 percent fat calories. This may vary slightly depending on the exercise goals or the sport. Most athletes should consume about 200 to 300 grams of carbohydrates a day or more. Excess carbohydrates, over the body's energy needs, can be converted to stored fats and burned for energy after the first twenty minutes of exercise.
Foods high in carbohydrates are fruits, breads, grains, pasta, vegetables, fruit juices and dairy foods. Let's look at the carbohydrate content of some selected foods.
You can achieve a daily carbohydrate intake of 250 grams by eating the following food groups:
Remember that fats offer no carbohydrate benefit but do supply calories.
The best high-carbohydrate foods -- vegetables, fruits, cereal, whole grains, pasta, rice and potatoes -- offer the body good nutrition as well as available energy. These foods should be consumed as part of a balanced diet. Severe calorie restriction, without proper exercise and diet balance, may lead to loss of muscle mass and fitness. Food, particularly carbohydrates, is an athlete's asset.