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University of Birmingham Sport
Introduction to Nutrition
We all know that we must eat. Consuming the right foods is essential for you to recover from your
exercise and training bouts, and since it is during the recovery period that we actually improve our fitness you can see why fuelling yourself appropriately is essential.
Starting with the basics there are three macronutrients that we need in our diet, these are Carbohydrate, Protein and Fat.
Carbohydrate
Carbohydrate foods are the body’s primary source of energy, and are vital in fuelling high intensity
exercise. One gram of carbohydrate contains approximately 4 kilocalories. Carbohydrates are composed of carbon, hydrogen and oxygen atoms joined together to form a molecule. The Carbohydrate
molecule can be stored in the liver and muscles as glycogen, this glycogen can then be broken down
to supply energy when the demand is there, although this storage capacity is limited. Carbohydrates
can generally be grouped into two categories; simple and complex. Simple carbohydrates are foods
such as cakes, biscuits as well as fruits and fruit juices. Complex carbohydrates on the other hand
are readily found in starchy foods such as bread, pasta and rice.
When carbohydrate is consumed the blood sugar level rises above a level that the body considers
normal, and insulin is secreted from the pancreas. The secretion of insulin then causes blood sugar
levels to return to normal. Carbohydrates can also be classified based on the extent of the insulin response (the release of insulin following the consumption of carbohydrate foods). This is known as the
Glycaemic index or GI for short. Foods that cause a large insulin response are labelled high GI, and
the energy that they provide is released into the bloodstream very quickly. Low GI foods as you have
probably guessed cause a much smaller insulin response and the energy that they supply is released
into the bloodstream at a much steadier rate. The glycaemic index gives foods a GI rating from 1-100,
with 100 being very fast release and a large insulin response, and 1 being a very slow release with a
virtually non-existent insulin response.
Using this knowledge you can then manipulate your carbohydrate intake to fit your training and exercise sessions. In the period before and after your workout you ideally need high GI foods to provide
you with a quick source of energy or to help replace depleted glycogen stores that have been used
during exercise. Low GI carbohydrates should then be used at all other times of day. Carbohydrates
(mainly complex low GI) should make up around 50-55% of your dietary intake to fuel your training.
Protein
Protein, like carbohydrate contains roughly 4 kilocalories per gram, however unlike carbohydrate it
cannot be stored in the body. Although protein forms the main constituent of our body tissues, so this
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could be seen as the body’s storage mechanism. Protein functions in the human body to facilitate
the growth and repair of tissues, and that includes muscle, which may explain the elevated consumption amongst the body building population. Even if gaining muscle mass is not one of your
training goals you cannot neglect protein intake. Endurance training also causes significant damage to your muscles and connective tissue. For this reason protein is vital in fuelling the adaptations to training and repairing this damage.
The building blocks of protein are amino acids which are joined together to form a chain and consist of nitrogen, hydrogen and oxygen. Protein rich foods include all meat, fish and poultry. Eggs
and dairy products as well as nuts and beans also provide a fair helping. According to government
recommendations protein should make up 10-15% of your dietary intake, although for active individuals I would recommend more in the region of 20-25% to promote recovery in addition to muscle growth, if that is one of your goals.
Fat
Fat is often seen as the bad guy, but many people forget that it is an essential part of the diet. It
is a vital component of the membranes that surround our cells, as well as its role in maintaining
healthy skin and hair. Fat can also act as a reserve supply of energy if our carbohydrate stores
are running low, and since it contains 9 kilocalories per gram (over double the energy content of
carbohydrate and fat), it provides a very good reserve store. Fat like carbohydrate can be stored in
the body; however unlike carbohydrate the capacity is limitless.
Fats generally exist as Triglycerides, which consist of a glycerol molecule joined to three fatty acids. The fatty acids are made up of carbon and hydrogen atoms joined together in a chain. There
are three groups of fat, saturated, mono-unsaturated and polyunsaturated. The difference between
saturated and un-saturated fats is that the un-saturated variety posses a single double bond between the carbon and hydrogen atoms, whilst polyunsaturated possess more than one double
bond within their structure. As a general rule of thumb saturated fats are hard at room temperature, whilst unsaturated fats are liquid.
Saturated fats generally come from land animal sources, whilst unsaturated and polyunsaturated
can be found in oily fish, olives and nuts. It is recommended that fat should consist of 25-30% of
your dietary intake with more emphasis on the unsaturated varieties.
This article acts as a general introduction to general nutrition, for more specific advice and help
with these matters consult a member of the gym staff.
Simon Donovan
University of Birmingham SPORT
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