Nutrition - Free Fitness Library
Active nutrition
Get the ultimate from your nutrition to excel in your sport. Anita Bean answers your questions with extracts from the book Sports Nutrition For Women. Edited by Anita Bean and Peggy Wellington.
What's the best way to fuel my muscles?
For nearly all activities the most important source of energy is carbohydrate.
A low intake means low carbohydrate stores and can limit your performance,
while an optimal intake can produce a significant improvement in training
intensity, duration and performance. Carbohydrate is stored as glycogen
in the liver (approximately 100g) and muscles (approximately 30g) but,
unfortunately, in relatively small amounts. Your glycogen stores can
become depleted after 90-180 minutes of endurance activity, after 45-90
minutes of interval training, or after 30-45 minutes of high intensity
/ anaerobic activity. The consequence of depleted glycogen is fatigue!
Starting exercise with low or sub-optimal glycogen stores leads to:
* early fatigue
* reduced training intensity
* reduced training gains
* poor performance
* increased injury risk
* slower recovery
* 'burn out' or contribution to overtraining syndrome (if chronic)
How can I speed recovery?
Each time you exercise you use muscle glycogen and reduce your stores,
so the aim of
your recovery phase is to replenish your glycogen as efficiently as
possible before your
next workout. You need to consider the following:
* the amount of carbohydrate in your diet
* the type of carbohydrate in your diet
* the timing of carbohydrate intake.
How much carbohydrate?
At a consensus conference on sports nutrition at Lausanne in 1991, scientists
recommended that athletes consume 60% of energy intake from carbohydrate.
This
translates into 450g of carbohydrate for a person consuming 3000 calories
a day or
300g for someone consuming 2000 calories a day. In practice, most active
women will
need 5-10g of carbohydrate per kilogram of body weight depending on
the intensity of their training. The lower end of the range would be
suitable for a woman exercising for up to one hour; the upper end would
be suitable for an elite athlete exercising four or more hours a day.
In terms of quantity food intake, you can get 450g of carbohydrate from
30 bananas, 12 large potatoes or 10 chocolate bars! Not that such a
diet is advisable - this simply gives you an idea of the amount of food
that should be eaten. It is more realistic to plan your diet in 50g
portions of carbohydrate. Examples are given below.
Portions of food providing 50g of carbohydrate
* three slices of bread or toast
* one banana sandwich (two slices of bread and one banana)
* a 6oz baked potato with 4oz baked beans
* 2oz of breakfast cereal with 1/2 pint low fat milk
* 2-3 oz of raisins
* two or three bananas
* 1 pint isotonic sports drink
* two or three pieces of dried fruit or small cereal bars
* seven rice cakes
* 7oz of cooked pasta
* 6oz of cooked rice
* one bagel
* four or five oatcakes
Which are the best types of carbohydrate?
There are two main considerations here; first, the nutritional 'package'
provided by the carbohydrate source; and second, the speed at which
the carbohydrate is absorbed into the bloodstream.
From a nutritional point of view, the best choices are naturally occurring
sources of sugars (found in fruit, vegetables and milk) and of complex
carbohydrates (found in bread, potatoes, cereals, pasta and grains).
This is because they come with a 'package' of other nutrients such as
vitamins, minerals and protein and fibre (non-starch polysaccharides).
From a performance point of view, your choice of carbohydrate depends
on the timing of intake in relation to your workout. All carbohydrates
are broken down into simple sugars and transported as glucose in the
bloodstream, and so are equally capable of being taken up by the muscle
cells and made into glycogen. As far as glycogen manufacture is concerned,
then, it makes no difference whether the carbohydrate comes from packet
sugar or wholemeal bread. What you do need to consider is the speed
at which the carbohydrate is converted into blood glucose and transported
to the muscles. The rise in blood glucose levels is indicated by a foods
glycaemic index (GI): the faster and higher the blood glucose rise,
the higher the GI. The GIs of various foods are shown in Table 1.
Sometimes it is an advantage to consume high GI carbohydrate - for instance
during the first tow hours after exercise or towards the end of a long
hard workout when glycogen stores are low. Studies have shown that consuming
approximately 1g carbohydrate/1kg body weight within the two hour post-exercise
period speeds up glycogen refuelling and therefore speeds recovery time.
In contrast, there are times when it is beneficial to consume lower
GI carbohydrates in a form in which they are absorbed more slowly over
a long period (between workouts; 2-4 hours before a workout). This may
be achieve either by selecting moderate and low GI carbohydrates or
by combining high GI carbohydrates with low GI carbohydrates, protein
or fat. For example, combine rice (high GI) with beans (low GI); baked
potato (high GI) with tuna (protein); or bread (high GI) with cheese
(protein and fat).
To enable you to choose the right carbohydrates for the right occasion,
refer to table 1.
How often should I eat?
Eating five or six meals or snacks a day at regularly spaced intervals
will help to maximise glycogen storage and energy levels, minimise fat
storage, stabilise blood glucose and insulin levels and control blood
cholesterol levels. Each time you eat carbohydrate, insulin is produced
which allows glucose, amino acids and fatty acids to be removed from
the bloodstream and taken up by cells. Therefore, eating moderately
and frequently causes a relatively steady insulin release, whereas eating
most of your food in one or two large meals causes a more rapid insulin
release and less effective glycogen storage. There is also a greater
chance of some carbohydrates being converted into fat rather than glycogen.
When should I eat?
Before a workout. Eating a snack meal of low to moderate GI carbohydrate
(for example, past with chicken or beans) about two to four hours before
exercise will help prolong a moderate blood glucose rise. Then, eating
20-25g of high GI carbohydrate (for example, one or two bananas) just
prior to your workout will help increase blood glucose and sustain a
higher level for longer in the bloodstream. The optimal timing of this
will vary from 5-20 minutes before exercise, depending on the individual.
During a workout. If you are exercising hard for more than one hour,
consuming 30-60g of carbohydrate/hour can help delay fatigue and maintain
exercise intensity. The amount depends on your body size (the bigger
you are, the more carbohydrate energy you expend) and exercise intensity
(the harder you exercise, the more carbohydrate energy you expend).
This carbohydrate may be taken in either liquid or solid form. Some
people prefer to take a carbohydrate-containing drink, for example an
isotonic sports drink or diluted squash, while others prefer to eat
carbohydrate in food form, for example bananas and raisins, and to drink
water. The choice is yours.
After a workout. It is most important to start refuelling as soon as
possible after exercise, as this is when glycogen manufacture is at
it's most efficient. Studies have shown that eating carbohydrate (1g/kg
body weight) during the first two hours after exercise improves the
efficiency of the refuelling mechanism by 5% to 7%. Choose high GI carbohydrates
during this period, for example isotonic drinks, bananas, or rice cakes
and jam.
Table 1: The Glycaemic Index of various foods (glucose = 100)
| Fruit Raisins 64 Bananas 62 |
Fruit Grapes 44 Oranges 40 |
Fruit Apples 39 Cherries 23 Plums 25 Apricots 30 Grapefruit 26 Peaches 29 |
| Vegetables Sweetcorn 59 Parsnips 97 Potatoes, baked 98 Carrots 92 |
Vegetables Sweet potatoes 48 Crisps 51 Yam 51 |
|
| Dairy products Milk 32 Yoghurt 36 Ice cream 36 |
||
| Other Chocolate biscuits 59 Mars bar 68 Honey 87 Sucrose 59 Glucose 100 Orange cordial 66 |
Other Oatmeal biscuits 54 Sponge cake 46 |
Other Fructose 20 |
Sports Nutrition for Women is available from all good book stores priced £12.99 and is published by A&C Black.