Carbohydrate Manipulation To Optimize Performance Biology Essay

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This article is analyzing one of the macronutrients, carbohydrate, which contribute in increasing performance in marathon race and provide energy for recovering, especially in the first 6 days before the race and 3 days after the race. Marathon race is an endurance race which challenge human body's extreme. Proper nutrition is very important in increasing the performance. The ultimate goal of this article is trying to have a better performance in marathon race by manipulate suitable amount of carbohydrate intake.

To properly and accurately address the carbohydrate needed in between the race period, an athlete is selected as the target tester. This athlete is an Asian, male, 35 years old, 70 kilograms, and with 5 years of long run experiences.

Marathon is the 42.195 km long race which challenge runners' physical capacities and endurances.

The performances are fluctuated very much for many runners from the world records of 2:03:59 to the allowed time limited, like 6 hours. Some of them even drop out before reaching the finish line. There are several factors affecting the performance in marathon, like intensity, glycogen reserves, etc. From the point of view of nutrition, by manipulating the carbohydrate intake, the performance will be improved because it increasing the glycogen reserves.


Macronutrients are carbohydrate, free fatty acid and protein. They are the main energy sources for prolong exercises, like marathon. What is carbohydrate?

"Carbohydrates can be subdivided into several categories based on the number of sugar units present. A monosaccharide consists of one sugar unit such as glucose or fructose. A disaccharide (e.g., sucrose, lactose, and maltose) consists of two sugar units. Oligosaccharides, containing 3 to 10 sugar units, are often breakdown products of polysaccharides, which contain more than 10 sugar units. Oligosaccharides such as raffinose and stachyose are found in small amounts in legumes. Examples of polysaccharides include starch and glycogen, which are the storage forms of carbohydrates in plants and animals, respectively." (FAO/WHO, 1998).

It is a molecular which has carbon, hydrogen and oxygen atoms, the ration between hydrogen and oxygen is 2:1. For example, the lactose is C12H22O11. The common presentation form of carbohydrate is CHO. There are several basic functions of the carbohydrate, like as the energy fuel for muscle contractions, help in fat metabolism, as body structure, etc. This article will focus on the role of as energy fuel. Carbohydrate stored in body as muscle glycogen and liver glycogen and broken down into blood glucose which circulated through the whole body. As glycogen is limited, its reserve is not enough for running a marathon.

"For a 70-kg marathon runner, the total energy required to run a marathon, , is approximately 2950 kcal." (Rapoport I. B., 2010 October)

Like Rapoport B said, for a 70kg runner, the total energy needed is around 2950 kcal, which is around 740 grams of carbohydrate.

"Estimated carbohydrate combustion exceeded estimated glycogen stores in active muscle and liver (475 g = 375 g (muscle) + 100 g (liver)]. Therefore, total body glycogen stores were made available for combustion. All classes of energy substrates participate, but carbohydrate, not lipid, is the primary fuel for marathon running." ( Brien O., Viguie M. J., C. A., Mazzeo R. S., and Brooks G. A., 1993, pp. 1009-1017)

As shown in the above abstract, the glycogen storages are around 475 grams. That means all the glycogen stores in the active muscle and liver are not enough for a marathon, there are still 265 grams of CHO outstanding theoretically. Let's assumed there are still 300 grams of CHO needed before participated in the race. Thus carbohydrate loading is introduced and recommended for marathon runners.

SIX days before the race

Carbohydrate loading is a strategy which used by endurance athlete to maximize the storage of glycogen in muscles. Normally there are two phases in doing the carbohydrate loading. In the first phase, that is the 4th to 6th days before the competition, the athlete are trying to deplete the glycogen storages as much as possible by having less CHO food and do some exercise to further deplete the glycogen. In the second phase, that is 3 days before the race, the athlete is trying to have much high CHO food as possible.

There are different version of carbohydrate loading done by some researches. Some of them stress on restrict or completely deplete glycogen storage before overload the carbohydrate intake while others are ignore the depletion period of glycogen but still overload the carbohydrate intake. For the athlete in this article, it is suggested to have a moderate carbohydrate loading. By experience, a moderate carbohydrate intake could decrease the possibility of getting discomfort gastro-intestinal problems as well as getting injuries. The reason is with pretty low glycogen storage, the immunity system is weak and some discomfort feeling will occurred, like dizzy, etc. In those situations, it is easier in getting injured. Thus, for this athlete, it is recommended to have a low carbohydrate intake during the depletion period with the ratio of CHO : Other macronutrients is 20% : 80%. And during the overloading period, the ratio of CHO: Other macronutrients is 80%: 20%.

"Research has also shown that athletes involved in high volume intense training (e.g., 3-6 hours per day of intense training in 1-2 workouts for 5-6 days per week) may need to consume 8-10 grams/day of carbohydrate (i.e., 400 - 1,500 grams/day for 50 - 150 kg athletes) in order to maintain muscle glycogen levels. This would be equivalent to consuming 0.5 - 2.0 kg of spaghetti. Preferably, the majority of dietary carbohydrate should come from complex carbohydrates with a low to moderate glycemic index (e.g., whole grains, vegetables, fruit, etc). However, since it is physically difficult to consume that much carbohydrate per day when an athlete is involved in intense training, many nutritionists and the sports nutrition specialist recommend that athletes consume concentrated carbohydrate juices/drinks and/or consume high carbohydrate supplements to meet carbohydrate needs." (Kreider B. R., Wilborn D. C., et al., 2010 February)

As the marathon is an endurance and medium or high intense race, the recommended carbohydrate intake is around 8-10g/kg of body weight per day during the carbohydrate overloading days. And as this athlete is an Asian, it is believed that it needs a little bit lower carbohydrate, so it is suggested to take 8g/kg CHO per day. That is around 560 gram CHO within the 3 day meals.

Glycemic index is the index that indicate the relative glycemic effects of carbohydrates.

"Per gram of carbohydrate, foods with a high glycemic index (GI) produce a higher peak in postprandial blood glucose and a greater overall blood glucose response during the first 2 h after consumption than do foods with a low GI." (Jenkins D, Wolever T, Taylor R, et al., 1981)

As suggested by the abstract above, low to medium GI food with complex carbohydrate is better for absorption. And some high CHO fluid or drink is helping in loading the CHO. Below is some GI values reference food, and is better for choose for overloading the CHO.




95% CI

Breakfast cereals with 150 ml semi-skimmed milk

Mini wheats



45.1 - 73.7

Rice pops



67.5 - 91.9




65.7 - 86.9




50.2 - 67.4

Fruit &fibre



52.8 - 69.6


Breads with 5 g margarine (25 g available carbohydrate)




47.6 - 94.2

Hovis wholemeal



58.3 - 132.5

Hovis white



50.4 - 123.4

Waitrose stoneground wholemeal



40.0 - 91.4

Vogels sunflower &barley



50.0 - 90.8

White pitta



35.5 - 98.7


Breads with 10 g margarine (50 g available carbohydrate)

Hovis wholemeal



51.1 - 118.7

Hovis white



51.8 - 126.9


Pasta, rice and potatoes with 10 g margarine




33.4 - 52.2

Egg tagliatelle



42.9 - 64.1

Basmati rice



26.5 - 59.1

Basmati easy-cook rice



53.3 - 83.5

American easy-cook rice



25.5 - 73.3

Baked old white potato with skin



59.6 - 78.4

Baked old white potato without skin



81.9 - 114.5

Boiled old white potato



77.3 - 114.5

Boiled new potato



49.6 - 110.0

Boiled charlotte potato



59.8 - 101.8

Instant mashed potato



64.0 - 125.6

Mashed Desirée potato



77.3 - 127.5

(Aston M. L, Gambell M. J., Lee M. D., Bryant P. S. and Jebb A. S., 2009 Jun)

"In conclusion, we have demonstrated that modified CHO-loading protocols that begin with an exhaustive depletion exercise achieve greater muscle glycogen concentrations that will persist longer than nondepletion protocols (e.g., training taper)." (Goforth W. H., Laurent D., et al., pp. 2010 December)

As training taper will increase the glycogen storage in muscle, so it is suggested to have a 30 minutes of running with less intensity.

The Race Day

In the race day, normally the marathon starts very early, so the first thing to do is wake up earlier. And it is suggested to have a breakfast at lease two hours before the race started.

It is the last chance to overload the CHO intake before the race. It is very crucial have a suitable breakfast. The amount of food and the time are very important.

"When prolonged exercise will be performed, such as a marathon, taking carbohydrates immediately before or during exercise is also an effective method of improving endurance. Under such conditions, it is desirable for the athlete to ingest monosaccharides or oligosaccharides, because these are rapidly absorbed and transported to the peripheral tissues. On the other hand, intake of carbohydrates inhibits the degradation of fat, which is another energy substrate, by stimulating insulin secretion. This leads to impairment of energy production via lipid metabolism and accelerates glycolysis as alternate energy production pathway. As a result, the consumption of muscle glycogen will increase, and the intramuscular pH will decrease due to increased lactic acid production, which may lead to impairment of muscle contraction. Therefore, it is necessary to ingest carbohydrates that will not inhibit lipid metabolism. It has been suggested that supplements containing fructose, which cause less stimulation of insulin secretion and are unlikely to inhibit lipolysis, rather than common carbohydrates such as glucose and sucrose, may be better for improving endurance."

(Aoi W., Naito Y.and Yoshikawa T., 2006)

Although having high CHO food will stimulate the insulin secretion, it is not a problem if there is enough time for the digestion system to consume the CHO food and reduce the insulin to the normal level. Thus, it is restricted to have any food with the 2 hours before the race.

For this athlete, it is suggested to intake 2g/kg of CHO of the body weight, that is around 140 gram of CHO. It is moderate amount of CHO intake in some researches.

The below table shows the recommendation of the breakfast and when to take it. It is assumed that the marathon is started at 6:20am, and it stopped eating after 4:20am.





Two slices of bread with Jam



Sport Drink (Pocari, 150ml)



Two boiled potatoes



One Banana



Sport Drink (Pocari, 150ml)




During the marathon, glycogen and free fatty acid are the main fuel for this endurance race. It is assumed that this athlete will maintain his steady state in most of the time. It that steady state, the percentage of burning glycogen and free fatty acid is around 50% : 50%. And in this case, the glycogen storage of this athlete is estimated to provides him to run for about 35km. That means there are still 7km which needed extra CHO intake.

The below CHO intake is recommended. The honey is recommended as it has high content of fructose which will not stimulate the insulin secretion.




At about the 30km, 300m before the water stand.

One PowerBar Energy Gel


At about the 35km, 300m before the water stand.

Half of the PwerBar Energy Bar


At about the 40km, 300m before the water stand.

Honey (diluted with water) (100ml)




After the race

Replenish CHO is very important in the first 24 hours, especially in the first 2 hours.

It is recommended to replenish 6-10g/kg of body weight, that is around 420- 700g of CHO for this athlete with 24 hours. Because it is after the race, there is no performance issue, the only issue is about the fast recovery of the body, so it is recommended for this athlete to decide how much to take of the CHO as long as it is with the 420 -700g range. In the first 2 hours, it is suggested to take 1-1.5g/kg of high CHO every hour. That is around 70-105g of CHO.


Recommended Carbohydrate Intake

Rapid recovery after training session or multi-day competition, especially when there is less than 8 h until next session

Intake of 1-1.5 g/kg BM for every hour in the early stages of recovery after exercise, contributing to a total intake of 6-10 g/kg BM over 24 hours

(Minehan M. and AIS Sports Nutrition, 2004)


Marathon is a challenge which need proper nutrition for better performance. One of the contributions of the macronutrients is the carbohydrate. By manipulated how much of CHO need to be taken and when to be taken, the performance is most probably will be increased.