Download Carbohydrate and the athlete

Carbohydrate and the athlete
Carbohydrates are made up of sugars and starch and they should be the major energy providers in your
diet. Current recommendations aimed at the entire population state that carbohydrate should provide a
minimum of 47 percent of your total dietary energy (calories) with most of this coming from starchy
carbohydrates.1
Starch is a highly important nutrient in the diet and is the body's favourite "fuel". It is important because it
provides most of our glucose, which is the only fuel the brain can use. In addition, starchy carbohydrates
contain fibre and are very good at satisfying our appetites.
Carbohydrate and the athlete
A diet high in carbohydrates is particularly important for the athlete. We store very little glucose in the body
so it is vital to have a regular intake of starch. This is because starch is converted to glycogen and stored in
the liver and muscles. This glycogen is then used to meet muscles' energy needs by being converted back
to glucose when the muscles exercise.
If the muscles run out of glucose they can also burn body fat, but fat is not as efficient an energy source as
glucose. Therefore high levels of glycogen will help you exercise at your optimum level. On the other hand,
low levels will result in early fatigue and reduced exercise intensity.2
Good Sources of starch
bread
cereals
porridge oats
potatoes
beans
lentils
rice
pasta
noodles
Sugars
Sugar is available in many forms:
glucose - found naturally in fruit and vegetable juices
fructose - occurs naturally in fruit and vegetables and especially in honey
lactose and galactose - found in milk
sucrose - occurs naturally in sugar cane and sugar beet
maltose - available from fermented grain products
For more information on how certain foods affect blood sugar levels, see the section on glycaemic index.
http://www.bupa.co.uk/health_information/html/healthy_living/lifestyle/exercise/diet_exercise/carbohydrate.html
How much carbohydrate should you eat?
Although the general recommendation for the population is that carbohydrates should supply a minimum of
47 percent of dietary energy (calories), it is probably important for athletes to increase this. Many sports
nutrition experts suggest a minimum of 60 percent to 70 percent. 3
So how can you work how out many calories from carbohydrate you should actually be taking in on a daily
basis?
An easy method is as follows:
If your total calorie intake is, say,
3,000 calories/day
then calories from carbohydrate
3,000 X 60 percent
= 1800 calories
1 gram of carbohydrate = 4 calories
Therefore, 1,800 calories is equivalent to 450 grams of carbohydrate.
Your total daily calorie intake from all sources should, of course, be linked to your body weight. In other
words, you should be eating an amount that enables you to maintain your weight within its healthy range. To
check whether your weight is within its healthy range, try our online body mass index .
What about carbohydrate loading?
In recent years there has been much discussion about the effectiveness of "loading up" with carbohydrates
before endurance events. The aim of this is to increase muscle glycogen stores above normal levels so as
to delay the onset of fatigue during an event.
There does seem to be some merit in this approach4 and below is a suggested method for achieving
carbohydrate loading over a seven-day period prior to an event.
Day 1
Endurance training for one hour to deplete your muscle
glycogen stores.
Days 2,
3&4
Taper off your training and eat a moderate carbohydrate diet 5 grams to 7 grams per kilogram of body weight.
Days 5,
6&7
Taper off training further and rest. While doing this, have a high
carbohydrate intake - 8 grams to 10 grams per kilogram of
body
Your might want to experiment with this approach during training.
Carbohydrate intake while exercising
Glucose, itself, is not stored in the body. Once the available glucose in the blood stream and cells' plasma is
used up, the body then turns to its supply of glycogen. As mentioned earlier, your body has limited stores of
glycogen in muscles and liver ready for conversion to glucose. So, it is likely that for longer exercise
sessions - say, more than an hour - you are going to deplete your supplies of glycogen and, therefore, run
low on glucose.
Probably the best way to top up while actually exercising is with an isotonic sports drink (see section on
Fluid intake) as this will provide glucose, fluid and also sodium. An intake of between 30 grams to 60 grams
of carbohydrate an hour is recommended.5 This is about the maximum your muscles can take up from the
http://www.bupa.co.uk/health_information/html/healthy_living/lifestyle/exercise/diet_exercise/carbohydrate.html
bloodstream during exercise. Greater amounts have no further benefit. It is best to start taking in
carbohydrate soon after the exercise session begins because of the delay in absorption.
Carbohydrate intake after exercise
How long does it take to restore glycogen levels after exercise? This depends on:
how depleted your stores are after the exercise session
your fitness level
the amount of carbohydrate you eat
the extent of muscle damage
It is best to replenish depleted stores of glycogen by taking in carbohydrate as soon as possible after your
exercise session. During the first two hours, replenishment is most rapid and is approximately one and a half
times the normal rate.6,7 During the following four hours, the rate slows down but remains higher than
normal. Following this period, glycogen manufacture returns to the normal rate.
Restoring your glycogen levels as quickly as possible is very important, particularly if you train every day or
every other day. This will help you avoid fatigue and get the best out of your training. 8
Key points
For the athlete, carbohydrates should provide 60 percent to 70 percent of total dietary energy
(calories). Most of this coming from starch.
Simple sugar is not a good source of energy as it can upset the body's metabolism.
Starchy carbohydrates are the body's favourite fuel.
Glucose is the only fuel the brain can use and is the favourite for muscles.
Glucose is not stored in the body.
Glycogen, which is stored in the liver and muscles, is converted to glucose to provide energy for
physical activity.
Carbohydrate loading can help performance in endurance events.
Depleted muscle glycogen stores should be replaced as soon as possible after exercise, ideally
within two hours.
References:
1. Department of Health. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. HMSO.
1991.
2. Bergstrom, J. et al (1976), Diet, muscle glycogen and physical performance. Acta. Physiol Scand., vol. 71. pp.
140-50.
3. Williams, C. and Devlin, J.T. (eds) (1992), Foods, Nutrition and Performance: An International Scientific
Consensus (London: Chapman & Hall)
4. Sherman, W. M. et al. (1981), Effect of exercise-diet manipulation on muscle glycogen and its subsequent
utilisation during performance. Int. J. Sports Med., vol. 2, pp. 114-8.
5. Coggan, A. R. and Coyle, E. F. (1991), Carbohydrate ingestion during prolonged exercise: effects on
metabolism and performance, in J. Holloszy (ed.), Exercise and Sports Science Reviews, vol. 19 (Baltimore:
Wiliams & Wilkins), pp. 1-40.
6. Ivy, J. L. et al. (1988a), Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion. J.
Appl. Physiol., vol. 64, pp. 1480-5.
7. Ivy, J. L. et al. (1988b), Muscle glycogen storage after different amounts of carbohydrate ingestion, J. Appl.
Physiol., vol.65, pp. 2018-23.
8. Costill, D. L. (1985), Carbohydrate nutrition before, during and after exercise. Fed. Proc., vol. 4, pp. 146-54.
http://www.bupa.co.uk/health_information/html/healthy_living/lifestyle/exercise/diet_exercise/carbohydrate.html