There's a green light on the system of "carbohydrate loading" to prolong endurance during a marathon race . . . but a red light for those who misuse it.
In other words, carbohydrate loading can be a marathon runner's
life spring or a trap, depending on what foods are eaten.
"One of the biggest problems of a runner is that burning excessive calories gives many runners license to load up on the wrong foods, such as foods containing high amounts of fat," said registered dietitian Evelyn Tribole, a private consulting nutritionist. Tribole, herself a marathon runner, is also author of "Eating on the Run" (Life Enhancement Publications: $8.95), whose release will coincide with the second Los Angeles Marathon on Sunday.
Glycogen stores, which provide fuel to the muscles to work, are supplied by carbohydrate foods, such as fruits, vegetables and grains, not by fat or protein. "Several studies have shown that when glycogen stores have run out, exhaustion sets in," Tribole said.
Athletes, she noted, eat too much fat. "They eat as much fat as most average Americans--about 42%. And that's too much," Tribole said. "It's important to have a full amount of the stores of glycogen, and to do this you need 60% to 70% of calories in the diet derived from carbohydrates."
But not just any old carbohydrates will do. Studies have shown that complex carbohydrates, such as grains, legumes, fruits and vegetables, fill glycogen stores better than simple carbohydrates, such as those found in sugars.
Some of the classic complex carbohydrate foods are breads, cereals, pasta, potatoes, yams, legumes (such as lentils and split peas), other vegetables and fruits. Pancakes, which are popular among runners, are an excellent source of complex carbohydrates.
How much should a runner eat of these foods?
Whereas the average individual should eat normal amounts of the four food groups (two servings each of meat and dairy products and four servings each of grains and fruits and/or vegetables per day), the recommended amount for the active runner is 12 servings from the bread and cereal group and eight servings from the fruit and/or vegetable group, due to the excessive amount of energy expended in marathon-type running.
A word of caution when eating a large amount of fruits. "Excessive fruit intake causes a diarrhetic reaction and may prevent a runner from finishing a race altogether," Tribole said.
The positive value of the carbohydrate loading theory--the systematic method of first unloading and then reloading the body of glycogen stores before a race to prolong endurance--was given the green light only recently, when a study showed conclusively that the method (controversial up to now) actually does prolong endurance.
"The principle of 'carbo-loading,' as it is sometimes called, is to increase glycogen stores in order to run further, not faster, before hitting the proverbial wall," Tribole said. The expression "hitting the wall" refers to the point when energy stores are drained--usually at about the 20-mile mark, depending on the individual's training and physiological makeup.
The new carbohydrate loading format was based on a 1981 Ball State University study by William M. Sherman Ph.D., David L. Costill Ph.D. and William J. Fink Ph.D. The original form was introduced by a Swedish scientist in the late 1960s.
According to Tribole, this is how the basic format works:
Phase 1: Count down six days before the race.
Day 6: Run 90 minutes.
Day 5: Run 40 minutes.
Day 4: Run 40 minutes.
During days 6, 5 and 4 eat a normal diet of the four food groups (two servings meat; two servings dairy products; four servings or more fruits and/or vegetables; four servings or more breads or cereal.
Phase 2: Count down the next three days.
Day 3: Run 20 minutes.
Day 2: Run 20 minutes.
Day 1 (day before the race): Complete rest. (Light jogging is considered fine for keeping limber.)
During days 3, 2 and 1, eat a diet high in complex carbohydrates. The diet should consist of 12 servings or breads, grains or cereals, eight servings of vegetables and/or fruit and two servings or more of dairy products and two servings of meat. The total amount of carbohydrate should not exceed 625 grams a day.
"We have learned from research there is a topping-off effect on 625 grams a day of carbohydrates," Tribole said. "If you eat more than 625 grams a day at this time, there will be no proportionate increase in glycogen stores. To explain this, I like to compare it with filling your gas tank beyond the fill-up limit. It's just wasted."
Tribole also warns against foods containing high amounts of fat, such as fried foods, ice cream, butter, sauces and fatty meats.
"If you are not running as much as you are eating, the body will simply store excess fats. And who wants to go around with excess fat when you're running?" Tribole asked.