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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 per cent of your total dietary energy (calories)
with most of this coming from starchy carbohydrates.1Starch 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.
How much carbohydrate should you eat?
Although the general recommendation for the population is that carbohydrates should supply a
minimum of 47 per cent of dietary energy (calories), it is probably important for athletes to
increase this. Many sports nutrition experts suggest a minimum of 60 per cent to 70 per cent.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 per cent
= 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, Taper off your training and eat a moderate carbohydrate
3&4
Days 5,
6&7
diet - 5 grams to 7 grams per kilogram of body weight.
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 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 rat.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 per cent to 70 per cent 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.
Glycaemic index and the athlete
You can significantly improve your performance by eating the right mix of complex and simple
carbohydrates. Getting the right balance will give you an energy boost just when you need it and it is not
as hard to achieve as it might sound. All you have to know is a food's glycaemic index.
What is the glycaemic index (GI)?
Glycaemic index (GI) is a numerical system that tells you how fast a particular food triggers a rise in your
blood sugar levels. A food with a high GI will cause a fast rise in blood sugar while a food with a low GI
will bring about a slower rise.
Why is this important?
From a health point of view, sharp increases in blood sugar are thought to be undesirable because of the
effect this has on insulin levels. Diets high in simple carbohydrates and low in starch have been shown to
significantly increase the risk of developing diabetes, high blood fat levels, high blood pressure and heart
disease.1,2,3,4
Why is this important for the athlete?
For the athlete, knowing the GI of different foods is important for reasons other than just health. Getting
the balance between complex and simple carbohydrates right can significantly influence performance.
Many experts recommend a low glycaemic index meal one to two hours before an exercise session.5 It is
thought that the slower, more consistent, release of energy will improve performance by delaying fatigue.
It has also been found that low GI meals produce higher blood sugar and fatty acid levels during the latter
stages of exercise.6,7 For endurance sports, this is very advantageous.
During exercise, when blood sugar levels need to be maintained, one way to achieve this is to drink an
isotonic sports drink. This will provide glucose, which is quickly absorbed, fluid and also sodium.
After exercise, however, when muscles' stores of sugar (glycogen) need to be quickly restored, a high GI
food is a good choice. This is because the simple sugars contained in a high GI food are rapidly
absorbed into the blood stream. In turn, this rapid absorption stimulates insulin release and that results in
increased uptake by the muscle cells of glucose and their manufacture of glycogen.
So, knowing the GI of various foods can clearly help you plan your diet in a way that will help to optimise
your performance.
How is glycaemic index for a food worked out?
The glycaemic index of any particular food is worked out by comparing it with a "reference food" for which
a GI has already been established. In other words, the effect of the food being tested on blood sugar
levels is monitored at set intervals over a two-hour period and the results compared with the reference
food.
Glucose is the reference food normally used or, occasionally, white bread. It is possible that you may see
the same food with two different glycaemic index figures. If glucose has been used as the reference food,
the GI figure is lower than if white bread has been used. The reason for the difference is that pure
glucose is absorbed into the blood stream much more quickly than the complex carbohydrates in white
bread. However, both figures mean the same.
So, for example, baked potato has a GI of 85 (when glucose is used as the reference food) which means
that its effect on blood sugar levels is 85 per cent that of glucose. Therefore, baked potato have less of an
effect on blood sugar levels. The GI of glucose has been set at 100 and nearly all foods will fall below this
figure.
If white bread was used as the "reference food" the figure for the GI of baked potato would be 128. This is
because baked potato has a greater effect on blood sugar levels than white bread. White bread, when
used as the reference food, is given the notional GI figure of 100 and quite a number of foods will have a
higher GI figure than this.
Click here to view the GI of a range of foods
Which component in food increases blood sugar?
It is the carbohydrate in food which influences blood sugar levels. Carbohydrate is made up of various
simple carbohydrates and starch (see section on carbohydrate). Starch is referred to as a complex
carbohydrate because it is a large molecule made up of many different sugar units all joined together.
While simple carbohydrates are small molecules made up of just one or two sugar units.
Because of their small size and simple construction, simple carbohydrates are easily absorbed into the
blood stream. The result is a rapid rise in blood sugar levels.
In contrast, complex carbohydrates (such as starch) need to be broken down into their individual sugar
units before they can be absorbed. For this reason, they take some time to be absorbed into the blood
stream. The result is a much slower rise in blood sugar levels.
What about meals and glycaemic index?
We often eat meals made up of various foods, rather than just one food on its own, so how can you work
out the GI of the meal?
Various factors such as the fat, protein and fibre content of meals together with cooking methods can
influence the GI of the entire meal as these will influence how quickly absorption takes place from the gut
into the blood stream.
The following method for working out the GI of a whole meal has been suggested. 8 Calculate the total
carbohydrate content of the meal, then work out the contribution each individual food makes to the total
carbohydrate content. For example, the GI of an average breakfast is calculated below:
Food
Carbohydrate (g) % of total carbohydrate
Orange Juice (150 ml)
GI
Contribution to meal GI
12.5
26%
46
26% X 46 = 12
Weetabix (30g)
21
43%
69
43% X 69 = 30
Milk (150 ml)
7
15%
27
15% X 27 = 4
1 slice of toast
13
27%
70
27% X 70 = 19
Total
48
100%
Meal GI = 65
Key points
a high GI food has a more dramatic effect on blood sugar levels than a low GI food
rapid rises in blood sugar levels are undesirable and are linked to various health problems
(particularly diabetes)
low GI foods/meals should be eaten one to two hours before exercise
during exercise blood sugar levels can be maintained with isotonic sports drinks
a high GI food is a good choice immediately after an exercise session
Calories and the athlete
How many calories do we need each day?
The Department of Health recommends that men should take in around 2,550 kcalories per day and
women around 1,940 kcalories per day.1 These are averages and some people will need more and some
people will need less - it depends on how active you are. Really, the best rule of thumb is that your calorie
intake should be just enough to maintain a healthy body weight (see Weight management for the athlete),
no matter how active or inactive your life is.
Why do we gain or lose weight?
The only thing that influences whether we gain, lose or maintain weight is the number of calories we take
in compared with the number of calories our bodies use up. This is just as true for the athlete as it is for
everyone else.
Calories taken in
Calories used up
3,000 kcalories
2,500 kcalories
Gain weight
3,000 kcalories
3,500 kcalories
Lose weight
3,000 kcalories
3,000 kcalories
Stable weight
How are the calories used?
Even when we aren't exercising, we require energy just to maintain our bodies and their vital functions.
Without energy our bodies would cease to function.
The table below shows the energy usage of a sedentary person with a low level of physical activity:
% Energy
Function
Used
Basal Metabolic Rate (BMR) - energy used to fuel essential activities such as
65%
breathing, organ and cellular function during rest or while asleep
Thermogenesis - energy used to digest and metabolise food and maintain body
10%
temperatures
Physical activity - energy used for movement, for example walking, running, lifting and
25%
pulling
Energy balance
Not only is it important to make sure that you are eating just enough calories to keep your weight healthy,
but it is also important to make sure that you get the energy from the right sources. The foods and drinks
we take in supply energy from four main sources.
Food source
Calories per gram
Fats
9 kcalories per gram
Carbohydrates
4 kcalories per gram
Protein
4 kcalories per gram
Alcohol (for some people)
7 kcalories per gram
For the body to work at its peak you should try to have the right foods and drinks. For your diet and
calorie intake to be balanced you should aim for:
Food source
Contribution to daily calorie intake
Fats
No more than 33 percent
Carbohydrates
At least 47 percent
Protein
Roughly 15 percent
Alcohol
No more than 5 percent
For people who do not drink alcohol the percentage calorie intake from carbohydrate should be
increased.1
And for athletes, experts recommend that you should increase your energy contribution from
carbohydrates to roughly 60 percent and decrease your intake of fat by the corresponding amount. 2
Key points
aim to keep your body weight within its healthy range
weight loss, gain or maintenance depends on the number of calories taken in compared with the
number of calories used up
calorie intake should not come from just one energy source but from a range of sources and
foods
the balance between carbohydrates, fats, protein and alcohol taken in is important in helping the
body to work at its peak.
| health information | health living | lifestyle | exercise
Vitamins and minerals and the athlete
For a long time it was believed that the body only needed proteins, fats, carbohydrates and a number of
minerals to stay fit and healthy. But then it was discovered that these dietary components were not
enough - tiny amounts of other materials were essential to keep the body functioning. These vital
ingredients were named vitamins.
Vitamins - what are they?
Vitamins are organic compounds that help regulate fat, carbohydrate and protein metabolism in the body.
They cannot be made by the body and have to be provided by the food we eat - fortunately we only need
tiny amounts of these vitamins.
Vitamins are not an energy source, but they play a vital role in releasing the energy stored in the other
foods we eat. In addition, our enzyme, nervous, hormonal and immune systems are dependent on
vitamins for regulation and control. Because of this vitamins are essential for good health, wellbeing and
growth.
Vitamins are divided into two types: water-soluble and fat-soluble.
Water-soluble: These vitamins cannot be stored in the body and need to be replaced regularly
through our diet.
Fat-soluble: These vitamins are stored in the body and include vitamins A, D, E and K.
Although these vitamins can be stored, they should still be part of a healthy diet
Minerals - what are they?
Minerals are inorganic elements that have many roles in the body's functioning. Apart from their more
well-known roles in the formation of strong bones and teeth, they also help to control the nervous system,
fluid balance in tissues, muscle contractions, some hormonal functions and enzyme secretion.
Minerals are as essential as vitamins and, just like most vitamins, they cannot be made in the body. All
our bodies' mineral needs have to be supplied from our diets.
Where do we get our vitamins and minerals from and what role does each play?
Vitamins
Function
Food sources
Vitamin A
Necessary for vision in dim light,
Fish liver oils (for example cod
(found in two forms:
for healthy skin and surface
or halibut liver oil), liver, carrots,
retinol and beta carotene)
tissues, especially those which
fortified margarine, cheese and
excrete mucus (for example the
dark green leafy vegetables
intestines, lungs and vagina). In
addition, it prevents infections
and is necessary for the
immune system
Vitamin D
For the growth and maintenance
Oily fish, eggs, milk, fortified
(found in two main forms:
of bones and teeth through
breakfast cereals and fortified
cholecalciferol and
regulation of absorption and
margarine. Also created in the
ergocalciferol)
metabolism of calcium
body by action of sunlight on the
skin
Vitamin E
Protection of cell membranes
Vegetable oils, eggs, whole
(found as a group of compounds
and fats from oxidative damage;
grains, green vegetables and
called tocopherols)
protection of vitamin A, immune
nuts
system and nervous system
Vitamin K
Is necessary for normal blood
Dark green leafy vegetables,
(covers a number of
clotting and energy metabolism
liver, meat, potatoes and
compounds, including
cereals
phylloquinone)
Vitamin B1
For energy metabolism,
Bread, potatoes, milk, meat
(thiamin)
especially from carbohydrates
(especially pork), offal, whole
grain cereals and fortified
breakfast cereals
Vitamin B2
Essential for the utilisation of
Milk, meat (particularly liver) and
(riboflavin)
energy from foods, especially
eggs
fats and proteins
Niacin (also known as vitamin
Necessary for energy
Meat, potatoes, bread and
PP)
metabolism
fortified breakfast cereals
Pantothenic Acid (also known
Energy metabolism and
Yeast, liver, whole grains,
as vitamin B5)
production of neurotransmitters
greens and nuts. In fact it is
for the nervous system
found in virtually all foods
Vitamin B6
Necessary for protein
Potatoes, vegetables, meat,
(found as a group of
metabolism, particularly of
milk and fish
compounds, including
haemoglobin
(nicotinic acid)
pyridoxine)
Vitamin B12
For the production of blood (red
(found as a group of
cells), nervous system,
Liver, milk, fish and eggs
compounds, including
synthesis of DNA
cyanocobalamin and
hydroxocobalamin)
Folic Acid (also known as
Necessary for the production of
vitamin Bc or M)
blood (red cells), nervous
Offal and raw green vegetables
system, synthesis of DNA
Biotin (also known as vitamin H)
For protein and fat metabolism
Liver and kidneys, whole grains
and nuts
Vitamin C
Necessary for the maintenance
Fresh fruit, especially citrus
(found as a group of
of connective tissues (including
fruits and vegetables
compounds, including ascorbic
tendons, ligaments and
(particularly potatoes)
acid)
cartilage). In addition, it helps
wound healing, production of
hormones, the immune system
and protects vitamins A and E
Minerals
Function
Food sources
Sodium
Helps regulate body fluids and
Salt, bread and cereal products,
is involved in energy release,
bacon, ham, shellfish, smoked
functioning of nerves and
fish, soy sauce and foods that
muscle contraction. Increases
have been preserved by using
blood pressure
salt
Is used in the body's fluid
Potatoes, vegetables, greens,
balance and is involved in
pork, dairy products, fruit
membrane functions, muscle
(especially bananas) and juices
Potassium
function and reduces blood
pressure
Calcium
Magnesium
For bones and teeth, blood
Milk, cheese, bread and flour,
clotting, hormone secretion,
green leafy vegetables and
muscle and nerve function
small oily fish with bones
Involved in muscle tone and
Milk, bread, potatoes and
activates enzymes
vegetables
Iron
Necessary for the manufacture
Red meats, liver, flour and
of haemoglobin in blood (red
cereal products, potatoes and
cells) oxygen transport and
vegetables
transfer to tissues, activates
enzymes
Zinc
For growth, bone metabolism,
Meat, liver, seafood (especially
activation of enzymes, release
oysters) milk, bread and cereals
of vitamin A from liver, immune
system, taste and insulin
storage
Copper
Essential for enzyme function,
Oysters, mussels, whelks, liver,
especially blood formation, bone
brewer's yeast, whole grains,
metabolism, immune system,
nuts and cocoa
nerve function and energy
metabolism
Manganese
Necessary for enzyme
Wholemeal bread, wheat germ,
activation and cell structure
nuts, avocados, peas and tea
(works with calcium and iron)
Molybdenum
Involved in enzyme functions
Liver, kidney, wheat germ,
lentils, sunflower seeds, eggs
and beans
Selenium
Has an enzyme function
Nuts (especially brazils), seeds,
protecting cell membranes and
bread, fish and meat (especially
fats from oxidative damage
pork)
(works with vitamin E)
Chromium
Enhances the action of insulin
Egg yolk, liver, cheese,
on glucose uptake by cells
wholemeal products, molasses
and brewer's yeast
Iodine
Phosphorus
A necessary component of
Oily fish, seaweed, meat, milk
thyroid hormones
and iodised table salt
Accommodates energy stores,
Dairy products, eggs, meat, fish,
bones, membrane function and
soya beans, soya products,
growth
pulses and wheat bran
Am I getting enough?
Most experts now agree that a balanced diet should provide you with all the vitamins and minerals you
need. This is provided you eat a variety of foods from each of the food groups (see section on balanced
diet) and, of course, in sufficient quantity. By quantity, we mean enough food for you to maintain a
healthy body weight. To check that your body weight is in the correct range for your height, why not try
our online body mass index (BMI) calculator.
Clearly, different people have different requirements and, because of this, helpful guidelines have been
established by the Department of Health.1 These are called Dietary Reference Values or DRVs. For any
particular nutrient (where the scientific information is available) there are three values.
LRNI (Lower Reference Nutrient Intake). This is for a small number of people who have low
needs and represents about 3 per cent of the population. Most people will need more than this.
EAR (Estimated Average Requirement). Is the amount of a nutrient needed by an average
person. So many people will need more and many will need less.
RNI (Reference Nutrient Intake). The amount of a nutrient that should cater for the needs of 97
per cent of the population. It is more than most people require and only very few people (3 per
cent) will need more. This is also known as the Recommended Daily Amount or RDA. It is this
value you will see on the sides of cereal packets.
It is important to remember that DRVs are aimed at populations of people, not individuals. As such they
are guidelines and not targets for you to aim for.
Athletes - do they have different requirements?
Generally speaking, like the rest of us, athletes should get all the vitamins and minerals from their diet.
Because athletes use up more energy than inactive people, they probably eat more too, and so any
increased requirement for vitamins or minerals should be met by their increased food intake (providing
the diet is balanced).
However, some studies2,3,4 have shown that many athletes don't have adequate vitamin and mineral
intakes. This may be because they restrict calorie intake in order to manage weight. Other reasons for
inadequate vitamin and mineral intake include irregular training routines that making meal planning
difficult and following a dietary "fad" that is not providing a balanced diet.
Will vitamin and mineral supplements enhance athletic performance?
A lot of work has been carried out to try to establish whether vitamin and mineral supplements improve
athletic performance. So far, there is little evidence that any improvement occurs in athletes who are well
nourished. The only improvements observed have been in people whose diets were previously deficient
in one nutrient or another, adding supplements just brought them up to their optimum level.
In summary, if you are not deficient in any vitamins or minerals, then supplementing your diet will not
bring about any improvement in performance. Nevertheless, if you do have some sort of deficiency, then
correcting this may well be of benefit.
Choosing a supplement
Most people will probably not be aware of any minor vitamin and mineral deficiencies as the symptoms
may be slight, while gross deficiencies are very uncommon in this country.
Nevertheless, you may want to take a supplement as an "insurance policy", based on the principle that,
at the very least, it will not harm you and may possibly be of benefit. If you do decide to take a
supplement then it is best to choose a well formulated multi-vitamin and mineral supplement that
contains all the main vitamins and minerals.
What about specific vitamins or mineral supplements?
It is best not to use supplements that contain just one or two specific vitamins or minerals. This is
because vitamins and minerals work in harmony and an excessive amount of just one can impair the
absorption or effectiveness of others. Correct balance is important.
Furthermore, some vitamins, particularly the fat-soluble vitamins, can be harmful in excess quantities as
they tend to build up in the body and cause problems. With water-soluble vitamins, amounts over and
above the body's requirements are simply lost from the body in urine and do not provide any additional
benefit - so you will be wasting your money!
You will notice on the packaging of supplements that for each particular vitamin or mineral it may list the
"% of RDA". RDA simply means the Recommended Daily Amount so, for example, if say for Vitamin C it
says "100% RDA", this means that it contains 100 per cent of your daily allowance. The RDA is similar to
the RNI in Dietary Reference Values.
You will probably notice that many supplements exceed the RDA, however, this is not necessarily
harmful as the safety margins are very high and well-formulated supplements are well within the
acceptable range. RDAs were formulated to cater for the vast majority of a population (nearly 100 per
cent). This means that many people will require less. However, RDAs were also set at a level where it
was known that there were no adverse effects.
Key points
Most vitamins and all minerals cannot be made by the body, so need to come from your
diet
A balanced diet should provide you with all vitamins and minerals you need
If you are well nourished already, supplements will not improve performance
If you are slightly deficient in some nutrients, a supplement may benefit performance
Gross vitamin deficiencies are rare in this country
The fat-soluble vitamins, A D E and K, may cause side-effects if taken in very high
quantities
When choosing a supplement choose a well-balanced multi-vitamin and mineral
supplement
Supplements containing a single vitamin or mineral are best avoided because it is difficult
to get the balance right