Image adapted from Sergio Piquer Costea 

Animal proteins (read beef steaks) were believed to be the best diet for athletes in the past. Nowadays, plant-based carbohydrates (read bowl of pasta) are default diet of any marathon runners.

History of carb-loading
During 1923 Boston Marathon, scientists found that majority of marathoners tested had low blood sugar levels (hypoglycemia) after the race. In the next Boston Marathon, a few runners were encouraged to consume high-carbohydrate food. Consuming high carbohydrate prevented lower glucose level and improved running time to complete the race.¹

The winner of both of those Boston marathon was Clarence DeMar, who won Boston marathon seven times.  We don’t know if DeMar participated in previously mentioned medical studies done in the Boston Marathon. However, he is widely believed to be one of the first runners, who unwittingly practiced carb-loading diet that included a dozen oranges,¼ pound of pine nuts, and 1 pound of caramels.

Four years before, scientists had reported athletes who consumed a carbohydrate-rich diet instead of a high-fat protein diet found exercise easier.² These studies showed the importance carbohydrates as a source of body fuel during the intense physical activity.

Carb-loading Recommendations
The marathon season is upon us and runners are advised to ensure adequate carb intake days leading up to the big race (before 6 hours) and as soon as they pass the finish line.³

According to the International Olympic Committee, optimal level of recommended carbohydrates for an athlete is ¾ to 1 pound everyday per 100 lb of body weight. A high carbohydrate diet usually means more than two-third of energy for body are obtained from carbohydrates.

Is carbohydrate an essential nutrient?
Carbohydrates are an important source of energy for living organisms, but they are NOT essential nutrients for humans.⁴

“The essential nutrients for humans are water, essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine), essential fatty acids (linoleic and α-linolenic acids), vitamins (ascorbic acid, vitamin A, vitamin D, vitamin E, vitamin K, thiamine, riboflavin, niacin, vitamin B-6, pantothenic acid, folic acid, biotin, and vitamin B-12), minerals (calcium, phosphorus, magnesium, and iron), trace minerals (zinc, copper, manganese, iodine, selenium, molybdenum, and chromium), electrolytes (sodium, potassium, and chloride), ultra-trace minerals, and source of energy (carbohydrate, fat, or protein).”

In theory, carbohydrate consumption is not required by humans. However, in its absence fats are broken down to supply energy into glycerol (instead of glycogen) and ketone bodies as source of energy for the central nervous system. This results in ketosis, often detected as volatile fruity smelling acetones in the breath and urine. Prolonged ketosis may lead to ketoacidosis, where body accumulates keto-acids leading to acidification blood (which is not healthy). Ketosis can be prevented by a daily intake of at least 2 ounces for adult. However, practically the minimal carb intake is recommended at ⅓ lb per day.  Beside bread, pasta and rice, carbohydrate-rich foods include in fruits, sweets, beans, potatoes, etc.

Why carb-loading works?
Studies have indicated the role of muscle glycogen to benefits of carb-loading. Glycogens are polymer storage form of glucose in animals similar to the starch in plants. The improved performance after the high carbohydrate diet is attributed to the higher muscle glycogen concentrations after such diet. It is generally accepted that carbohydrate consumption can improve endurance capacity, i.e., time to exhaustion, as well as enhances physical performance.

For the prolonged physical activities (marathon), the mechanism behind performance improvement is probably due to the maintenance of blood sugar levels by carbohydrate oxidation. The mechanism behind the carbohydrate intake and performance enhancement during high intensity exercise (sprint run) is unclear.⁵

Initially, low blood glucose levels (hypoglycemia) were suspect as cause of development of fatigue. However in 1980s, researchers could not clearly link hypoglycemia with fatigue. Nevertheless, benefits of carb-loading on endurance were consistently demonstrated.

How should athletes carb-load?
The introduction of high-carb commercial “sports drinks” (read Gatorade) and rejuvenation in research on the effects of carbohydrate while exercising during 1980s, led to the practice of consuming high-carb diet during the long exercise. Slowly, it became a norm in of the endurance sports culture, such as marathon.

The combinations of easily absorbed form of carbohydrate in intestine, such as glucose and fructose, are shown to be the most effective form of “carb-loading”. The extra carb should give adequate energy during the exercise without being burden to the stomach – the type of carb doesn’t matter much. The most importantly, athletes should carb-load on their favorite pre-competition carbohydrate meal, be it their grandma’s homemade pasta or bowl of rice that remind them of home.

Image: Steve Johnson and IRRI Images 

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