Nutrition
Swimming is a very demanding sport and it is important that you manage your energy
and protein intake to enable your body to cope with training and competition. You
probably get advice on what is a good or bad diet from a school dietician, or did so in
the past, but remember that the average dietician may not be familiar with the
demands of competition swimming: you will require significantly more energy to fuel
your muscles and protein to build and maintain your muscles than most other people.
Good sources of energy
Sugars
The ‘simple’ sugars, glucose and fructose, are the currency of energy for your body.
Both of these will fuel the processes of glycolysis and respiration that produce energy,
during which they are broken down to carbon dioxide and water. Glucose and fructose
are hexoses, in other words they are 6-carbon sugars; they also contain hydrogen and
oxygen. They can adopt linear or circular structures, and for those that like a bit of
chemistry, here they are:
The carbon atoms are not shown in these pictures but they are at every corner or
junction where nothing else is shown (you should be able to count 6). Both glucose
and fructose can exist as mirror images of the molecules shown in the diagram: the
two configurations are called the D form and the L form. All of the glucose and
fructose found in nature are in the D form. Sometimes the D form of glucose is called
dextrose, so for everyone except a diehard chemist, dextrose and glucose mean the
same thing. You may have seen dextrose energy tablets, for example.
Energy drinks and tablets usually contain glucose, which is taken up rapidly by the
body and is available for the muscles to use in minutes after you have taken the drink.
This is fine if you are training or about to race, or to replenish your energy levels just
after a race, but not a good idea if you are sat on the sofa at home, because eating or
drinking too much sugar without exercising is linked with an increased risk of
developing obesity and Type 2 diabetes. Energy drinks and tablets are also expensive,
and for everyday training they are not necessary. If you do use them in training, sip
them during a hard set and use water to keep hydrated. The energy drink will then last
a few sessions. For a good, alternative, everyday energy and rehydration drink, dilute
your favourite fruit juice 1 in 4 in water: fruit juices contain lots of fructose as well as
glucose, and another simple sugar: sucrose. Squash also contains lots of sucrose, often
added to make it sweeter.
Sucrose is the sugar that plants make in photosynthesis, using energy from sunlight,
and it is the sugar that is extracted from sugar cane and sugar beet and is in the packets
of sugar in kitchen cupboards. It consists of a molecule of glucose joined to a
molecule of fructose, and here it is:
Once again, the carbon atoms are not shown in this picture to make it less cluttered,
but they are at every corner or junction where nothing else is shown. Because it
consists of two smaller sugars joined together, sucrose is called a disaccharide.
Another disaccharide you might come across is maltose, which is two glucose
molecules joined together. Sucrose is present in lots of foods, but most obviously
sweets, confectionary and fizzy drinks like cola. It also sneaks into a lot of foods that
you might not expect, not just because of its sweet taste but because it acts as a
thickener. Sucrose is a good rapid energy source because your body has a very
efficient and fast-acting enzyme called invertase that cleaves sucrose into glucose and
fructose molecules which are then available for glycolysis and respiration. So similar
advice applies to sucrose as to glucose and fructose themselves: use sugary drinks and
sweets when you need energy rapidly and limit your intake at other times to an
occasional treat.
Starch
As I said, maltose is a disaccharide of two glucose molecules joined together. It
doesn’t end there: in theory there is no limit to the number of glucose molecules that
can join the chain. Molecules with lots of simple sugars joined together are called
complex carbohydrates (carbs for short), and there are a whole plethora of them.
Eventually the chain gets so big that the molecule becomes insoluble, and plants and
animals use insoluble complex carbohydrates to store energy and, in the case of plants,
make cell walls. The most common plant storage carbohydrate is starch, which
consists of straight chains of glucose molecules called amylose and branched chains
called amylopectin. Here they are, once again with most of the carbon atoms not
shown:
These diagrams show short glucose chains; in reality, a starch molecule would contain
many thousands of glucose units. Animals (including humans) make a very similar
complex carbohydrate called glycogen, and this acts as an emergency energy source
for your muscles. Starch from different sources does differ in the amount of
amylopectin and amylose it contains, but not by much.
Good sources of starch are all of the cereal grains (wheat, rye, barley, maize, rice), and
potatoes. Bread and pasta, of course, are made from wheat flour, so are excellent
sources of starch. Watch out for breakfast cereals and cereal bars, though, some of
which also contain loads of sugar (read the label!). Cakes are made from flour but also
contain a lot of sugar and fat.
When you eat a starchy food, enzymes called amylases in your digestive system start
to break it down. Some chop the strands up and others nibble glucose units off the end.
This means that glucose will be released from the starch steadily over a period of a
few hours. So if you have a sandwich, baked potato, pasta, bowl of cereal or bowl of
rice an hour before training your body will get a steady supply of glucose right
through the session (starch is sometimes called a slow-release carbohydrate).
Similarly, a bowl of cereal and some toast on the morning of a meet will start you off
nicely to manage your energy demand through the day. Pasta has been touted as being
particularly good for athletes, but the starch in pasta is the same as that in bread and
not much different from that in potatoes and rice.
Maltodextrin
Maltodextrin is made from starch by partly digesting it with amylase enzymes to make
short chains of glucose molecules (glucans). It is used as a food additive but is also
sold by some sports nutrition manufacturers. It is a white powder but unlike starch it
will dissolve in water, so you can make up an energy drink with it. It should provide
energy a bit more slowly than a sugary sports drink. It is only available from specialist
sports outlets, is not cheap and doesn’t taste particularly nice on its own, so you will
probably have to flavour the drink with some sort of squash. Since the squash will
contain sucrose, the combination could provide you with fast- and slow-release
energy. Maltodextrin is popular with long-distance swimmers and triathletes who
require energy for a sustained period and Georgie Halford used it for her Channel
swim.
Glycaemic index (GI)
The glycaemic index is an indicator of how fast energy (or sugar) is released from a
food, so you may see food referred to as high or low GI. A sugary sports drink, for
example, will be very high GI, while starchy foods will be medium and a salad would
be low. High GI foods provide you with energy very quickly so should be used only
when exercising or as an occasional treat.
Fats and oils
You may well have been told that fat in food is bad for you because it will make you
fat and is associated with a risk of heart disease. This is an over-simplification. Fats
are certainly the most energy-dense foods in our diet, so people who are trying to lose
weight often avoid them as much as they can. However, the body can inter-convert
sugars, complex carbohydrates and fats, and if you take in more energy in your food
than you burn up in exercise, whatever form the energy comes in, your body will store
that energy in the form of fat. So sugars and complex carbohydrates can make you fat
just as well as fat can. It is true that too much saturated fat (which we will come to
later) in the diet is associated with a risk of heart disease, but that risk is greatly
reduced by exercise. It is also true that some fats are essential for our bodies to work
properly. Indeed, the minimum fat content of the human body is around 2-5 % for men
and 10-13 % for women. In reality, most people have higher body fat content than
that, with male athletes typically having 6-13 % and female athletes 14-20 % body fat.
Fats and oils are essentially the same thing, except that fats are solid and oils are
liquid. They are made up of fatty acids, which are long hydrocarbon chains with a
methyl (CH3) group at one end and a carboxylic acid (COOH) group at the other.
Usually the fatty acids are linked in threes to glycerol molecules to make
triacylglycerols. Here is the structure of stearic acid, an 18-carbon fatty acid present in
a lot of animal (including human) fat and of triacylglycerol, in which the hydrocarbon
chains from the three fatty acid molecules are shown as R. The glycerol and fatty acid
molecules are linked by an oxygen atom. Molecules formed in this way are called
esters.
Saturated and unsaturated fats and oils
Different fatty acids are distinguished by chain length and the number and position of
double bonds between the carbon atoms in the chain. Carbon atoms joined by double
bonds are described as unsaturated, while those that are joined by single bonds are
saturated. Fatty acids in which all of the carbons are joined by single bonds are
similarly called saturated fats, while those with a single double bond are
monounsaturates and those with more than one are polyunsaturates. Plant oils contain
a variety of fatty acids with different chain lengths and degrees of saturation. Animal
fats, on the other hand, contain mostly saturated and monounsaturated fatty acids.
Unsaturated fatty acids can be subdivided according to the position of the first double
bond with respect to the methyl (omega) end, so Omega-3s, for example, have the first
double bond at position 3. Unsaturated fatty acids have a lower melting point than
saturated fatty acids, so are more likely to be liquid at room temperature; hence plants
tend to have oils while animals have fats.
Familiar fatty acids include oleic acid, an 18-carbon fatty acid with a single double
bond (a monounsaturate), that makes up a high proportion of olive and oilseed rape
oil. Other well-known plant fatty acids include lauric acid and palmitic acid, which
saturated and are the prevalent fatty acids in coconut and palm kernel oil, stearic acid,
a major component of cocoa butter, and linoleic acid, an omega-8 polyunsaturated
fatty acid which is found in sunflower and maize oil and makes up about 20 % of
oilseed rape oil. Animal fat is made up predominantly of stearic acid and oleic acid.
Essential fats
Some fatty acids play important roles in the body, particularly in the brain and nervous
system. If you have a baby sibling who is being given infant formula milk, have a look
at the label and you will probably see that EPA and DHA have been added. These are
abbreviations for very long omega-3 fatty acids, with excellent names:
eicosapentaenoic acid (EPA), which is 20 carbons long with 5 double bonds, and
docosahexaenoic acid, which is even longer, with 22 carbons and 6 double bonds.
These fatty acids are added to infant formula milk because foetal development
requires them, and these long-chain omega-3s are also important in the adult diet. The
human body can make them but the efficiency is low, so we should try to acquire them
in our diet. By far the best source is oily fish like mackerel. Fish don’t actually make
them but marine algae do, and they accumulate through the marine food chain and end
up in fish oils. You can also buy supplements containing these fatty acids but they are
expensive.
Omega-6 polyunsaturated fatty acids are also important in our diet. These include
lauric acid (18 carbons, 2 double bonds), which is in sunflower oil, and gamma
linolenic acid (GLA) (18 carbons, 3 double bonds), which is in evening primrose and
borage (sometimes called starflower) oil. You can also get GLA in supplements, but it
is expensive. Our bodies cannot make lauric acid and can only make GLA from lauric
acid. Lack of these fatty acids causes dry hair, hair loss and poor wound healing.
There is also a longer polyunsaturated omega-6 fatty acid that is important in our diet:
a 20-carbon fatty acid with 4 double bonds, called arachadonic acid. Arachadonic acid
is an important component of cell membranes and is abundant in our brain and
muscles. There is no plant source of arachidonic acid but it is present in meat and
dairy products. If you are a vegan, make sure that you get plenty of plant omega-6
fatty acids: our bodies will make arachadonic acid from lauric acid and GLA but the
process is inefficient. Some animals can’t do it at all: cats, for example, are obligate
carnivores (they have to eat meat) partly for that reason.
Fats as an energy source
Fat-rich foods include chocolate, full fat cheeses, cream, butter, cakes and pastries and
some cuts of meat. Since fats are the most energy-dense foods you might think that
these foods would be good to eat just before a training session or competition. The
problem with fatty foods, however, is that they are digested very slowly, so by the
time the energy is released you are on your way home. So stick to carbs for managing
your energy levels through training and competition. The one way that you might use
fatty foods is if you are in heavy training and are having trouble avoiding weight loss.
If that is the case, you should talk to your coach about it and get medical advice
anyway in case there is a more serious reason. In extremely demanding, long sports
events like the Tour de France, the athletes use fatty foods for the long-term
management of their energy levels and weight, while using carbs for short- and
medium-term energy. So before and during a stage they will eat carbs but in the
evening after a stage they eat fatty foods to try to meet the huge energy demand of the
two-week event.
Proteins
Proteins are the building blocks of our bodies and are important for athletes because
muscles are made up mostly of protein. We therefore require proteins to build muscle
and for our muscles to repair themselves after strenuous exercise. The enzymes that
catalyse the myriad chemical reactions that go on in our bodies are also proteins.
Proteins are made up of chains of amino acids; these molecules consist of a carbon
chain with an acidic (COOH) group at one end and an amino group (NH2) at the other.
They also have side chains and there are 20 different amino acids in proteins, all with
different side chains. Some of these side chains also contain nitrogen and in two amino
acids they contain sulphur.
Plants get nitrogen and sulphur from the soil and use them to make amino acids. The
nitrogen and sulphur is then passed up the food chain. Animals can only get nitrogen
and sulphur from food, but animals (including humans) can make some amino acids
from other amino acids. There are also some that we cannot make and these are called
essential amino acids, meaning that we have to get them in our diet.
Unlike carbs and fats, we cannot store amino acids. Any that we have in our food and
do not need to make protein are broken down and the nitrogen is excreted as urea
(NH2CONH2). We therefore need a continual supply of protein. In some countries this
is difficult to achieve and some people in developing countries do suffer from diseases
caused by amino acid deficiencies. In the UK, however, most people probably
consume more protein than they need. High protein foods include meat, eggs, dairy
products, grains, nuts, beans and pulses. Meat and dairy products, in particular,
contain not only lots of protein but the right balance of amino acids for us. Many
athletes favour white meat (poultry) and fish because it provides the protein with
relatively little fat. If you like red meat, go for lean cuts. If you do not eat meat or
dairy products, eat a variety of grains, nuts, beans and pulses; none of these provide a
perfect balance of amino acids but they are each deficient in different ways, so in
combination they can do the job.
The trick is to have protein when you need it, and you need it most after training and
competition. The extreme demands that you put on your muscles result in some
damage to the muscle fibres, which need to be repaired, and the stress that your
muscles undergo during training also encourages muscle growth. Having some protein
after training and competition therefore helps your muscles to recover and to adapt to
the hard work you are putting them through. There are lots of recovery sports drinks
on the market now, but essentially they are milky drinks with a few additives and milk
itself is a good recovery drink.
Vitamins and minerals
The chemical processes in our bodies require not only enzymes but a whole range of
complex nutrients and minerals to work properly. Some of the nutrients have to be
acquired in our diet and are called vitamins, subdivided into classes called A, B, C
etc.; severe deficiencies in them lead to a range of diseases, including scurvy (vitamin
C), beri beri (vitamin B1) and rickets (vitamin D). These diseases are now almost
unheard of in the UK but are still common in poorer parts of the world. Vitamin D is
unusual because our bodies can make it but only if our skin gets sufficient sunlight. In
high latitudes like the UK, we need some additional vitamin D from our diet,
particularly during the winter months, and good sources are oily fish, eggs and some
breakfast cereals that have vitamin D added to them. This is especially important for
people with dark skin. Fruit and vegetables provide lots of the other vitamins, and
meat and bread are good sources of some of the B vitamins.
The minerals that our bodies need include iron, sodium, potassium, calcium and zinc.
Sodium chloride is readily available as household salt, but you should make sure that
you get potassium as well: bananas are a good source. Both sodium and potassium
chloride are lost in sweat during exercise and this can lead to muscle cramps, so some
sports drinks contain them. Note that there is no point replenishing these salts unless
you hydrate as well, because your body will have to get rid of them, and if your sports
drink does contain them you may need to drink additional water: find out what works
for you. Too much salt can also cause high blood pressure, and, like sugar, salt is
present at sometimes high concentrations in foods where you don’t expect it, so make
a habit of reading food labels and control your salt intake.
Iron is present in the haemoglobin in our blood, amongst other things, and iron
deficiency causes anaemia. There is plenty of iron in meat, wholegrain cereals
(including wholemeal bread), many breakfast cereals (check the label), nuts, beans and
leafy vegetables, and stacks of it in liver (be careful with liver, though, because liver
also contains lots of vitamin A, which you can have too much of as well as too little).
Meat, wholegrain cereals and bread, many breakfast cereals, nuts, beans and leafy
vegetables are also good sources of zinc.
Calcium is important for cellular function and also gives our bones their strength in
the form of calcium phosphate. Good sources of calcium are dairy products and leafy
green vegetables.
‘Five a day’
Fruit and leafy green vegetables are mentioned several times in the vitamin and
mineral section, but many people in the UK do not eat them on a regular basis. The
‘five-a-day’ campaign addresses this by encouraging people to eat five or more
servings of fruit and vegetables every day. Try having some fruit with your breakfast
and including leafy green vegetables in your main meals, and have a piece of fruit as a
snack instead of sweets or crisps.
Dietary fibre
In the section on carbohydrates we talked about starch as an energy source. Plants
make lots of other complex carbohydrates, mostly to form part of their cell walls.
Cellulose is a well-known example and is very similar to starch in that it is made up of
chains of glucose models, but the bonds between the glucose molecules are different.
These bonds are not affected by the amylase enzymes in our guts that break down
starch, and for humans and most other animals, cellulose is indigestible (the
exceptions are ruminant animals, such as cows and sheep, and termites, all of which
have microbes in their gut that digest cellulose for them). The indigestibility of
cellulose and other similar molecules from plants means that they pass through the gut
without being digested and make up what is called dietary fibre. Perhaps surprisingly,
this appears to be good for us, and many scientific studies have shown dietary fibre
not only to help digestion but also to improve blood glucose control, cholesterol levels
and blood pressure. There is a lot of fibre in wholegrain cereals (including wholemeal
bread), beans, pulses, peas, jacket potatoes and some fruits, such as apricots.
What happens if you get it wrong?
First of all, enjoy your food. We are very lucky to live in a country and time where
food of all kinds is abundant and relatively cheap. Don’t stress too much about what
you are eating, but aim for your ‘five-a-day’ and try to eat a range of other foods to
give you balanced nutrition. As an athlete, the main difference between you and other
people is a high energy demand. Your body has energy stored in the form of fat and
glycogen (the carbohydrate in muscle) and these stores can be mobilised when needed.
This process involves the conversion of the fat or glycogen to glucose to fuel
glycolysis and respiration, and is given another excellent scientific name:
gluconeogenesis. You might think that the glycogen would be used first, but glycogen
is for emergency use only, and if your body can meet the demand for energy by
burning fat reserves, that is what it will do.
That is fine for moderate exercise, like walking, but gluconeogenesis is slow and fatburning alone will not provide the energy for heavy exercise. If you turn up for
training without having eaten some carbs, your body will have insufficient fuel to keep
going through the session. Your body will send signals to your brain that it needs to
stop, and you will feel tired, listless and lethargic, and will either float along at the
back of the lane or get out, telling the coach that ‘you just can’t get into it’. If you
force yourself to work hard, either through your own determination or because you are
afraid of upsetting your coach or parents, your body will resort to breaking down
muscle protein, using the carbon, hydrogen and oxygen to make sugars and getting rid
of the nitrogen in urine. Those beautifully toned muscles that you have spent months
strengthening in training quite literally end up down the toilet.
Forcing yourself to work hard in those circumstances is difficult, but competition is
different because as you build up for a race your body releases a hormone called
adrenalin. This hormone prepares you for extreme action and without it you cannot
perform at your best. One of the things that adrenalin can do is over-ride the signals
from your body telling your brain that it does not have enough fuel, and your body,
forced to keep going, resorts to using anything it can, including muscle protein. Here
is a scenario to avoid (and I have seen it happen just like this):
You wake up on the morning of a meet. Your nerves make you feel a bit queasy and
you don’t fancy breakfast so you head off without eating anything. During the warmup you are OK but in the sprints at the end you feel a bit lethargic. You worry that you
will swim badly and that makes you more nervous, and the queasiness comes back, so
you don’t eat anything. You head off for your first event feeling a bit off. You dive in
and your body suddenly faces a massive energy demand that it can’t meet. It sends
signals to your brain to say it is in trouble but these are over-ridden by the adrenalin
brought on by racing, so it scavenges any energy source it can find. You swim a bit
below your pb, and after the race, with the adrenalin gone, you feel terrible. You try
one more event but it is worse and you go home early. Everything settles down, you
regain your appetite, have something to eat and start to feel better. You are convinced
that you were ill and were just unlucky that it was on the day of the meet, but all that
really happened was that you failed to manage your energy needs through the meet,
and the same will happen next time if you make the same mistakes.
Here is a better scenario for a meet: You get up feeling nervous but know this is
normal and you make sure that you have a good breakfast: a bowl of breakfast cereal
and some toast, perhaps. Those carbs will be providing you with energy for the next
few hours. You head off to the meet and warm up. After the warm-up you have a gulp
of an energy drink and more carbs, perhaps some pasta, bread or rice, or maybe a
banana. You are all set. Before your first race you have another gulp of your energy
drink and after the swim you have another, plus a few more mouthfuls of your carbs.
At lunch you have a baked potato, or a baguette or more pasta (go easy on any fillings
or sauces; it is the carbs that you need). All goes well, and on the way home you have
a milky drink to help your muscles to recover so that they are ready for training the
next day.
Simple, so make sure that you get it right.
Summary
Eat a balanced diet with plenty of fruit and veg.
Use carbs to manage your energy needs through training and competition. A snack
with bread, pasta, rice or potato (boiled or baked) in it an hour before you swim will
get you through most training sessions.
Use sugary drinks only when you need energy fast, for example as a top-up during a
hard set or before a race.
Fats may be useful for long-term energy management if you are in heavy training.
Otherwise have them in moderation, but remember that some, like fish oils, are good
for you.
Use protein to help your muscles to recover after training or competition.
Don’t stress about your food: enjoy it!