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zone around GM farms in which no similar plants are grown.
This might just be possible in large countries like Canada, but is
impossible in smaller countries like the UK.
180 " 101 FACTS YOU SHOULD KNOW ABOUT FOOD
97. Amino acids are the basic materials from
which all living matter is made
ore than 100 amino acids occur naturally, but just 22 of
Mthem combine to make the millions of different proteins
which are so vital to life. When amino acids were first identified,
scientists thought there were just twenty involved in the making
of proteins. But in 1986, Ohio university scientists investigating
microbes that produce natural gas discovered another. They
called it selenocysteine. In 2002, the same group of scientists
found a 22nd amino acid in a very ancient kind of bacterial-like
microbe called Archaea. This acid they called pyrrolysine. Most
scientists think a few more will be found as they study other
microbes. All the same, these extra protein-making amino acids
are rare, and it s the original twenty that are crucial in the pro-
teins of the human body.
Proteins are some of the largest and most complex sub-
stances in the universe. There are thousands of different kinds
in the human body, and they perform thousands of different
tasks, from building structures such as hair and nails to control-
ling chemical reactions. Keratin, for instance, makes up nails and
many other parts of the body, while haemoglobin transports oxy-
gen through the blood in red blood cells. The simplest proteins
are made up of just four different kinds of amino acids. Most of
the more complex proteins are made from all twenty acids,
however.
The human body uses up proteins all the time. They are lost
through bodily waste, perspiration, the growth of hair and nails,
101 FACTS YOU SHOULD KNOW ABOUT FOOD " 181
and through many other processes. As a result, the body needs
a regular supply of new proteins, and it needs amino acids to
make them with. Green plants and some microbes can make all
the amino acids they need. But humans and most other large
animals can make only half of them. The ten or so amino acids
that the human body can make for itself are called non-essential
acids. The rest are called essential acids, and your body gets
them from the food you eat.
When you eat food, you are often taking in ready-made pro-
teins. But these proteins are not in a form that the body can use.
To use them, the body must first break them down in the diges-
tive system into the individual amino acids they are made from.
The body s cells then re-assemble them to make the necessary
proteins. Some foods are so rich in certain kinds of protein that
they contain all the essential acids the body needs. These pro-
teins are called complete proteins. Cheese, eggs, fish, meat and
milk are packed with complete proteins.
Other foods contain what are called incomplete proteins,
because they contain only some of the essential acids. Cereals,
vegetables and nuts are rich in incomplete proteins. Although no
single incomplete protein contains all the amino acids the body
needs, a combination of them might do. Cereals alone might
not provide all the right amino acids, but cereals combined with
the right vegetables may do. This is why a balanced diet is so
crucial to good health.
182 " 101 FACTS YOU SHOULD KNOW ABOUT FOOD
98. Food filled with chemicals that counter the
effect of oxygen could slow down the ageing
process
ou can avoid cigarettes, alcohol, caffeine, fats and all the other
Ythings that are said to be bad for you. But you can t avoid
oxygen  and this, some scientists say, is the chemical that ages
you most surely. Oxygen is highly reactive, and that s what makes
it so useful in the body. It s the vital element that helps body
cells release energy from sugar. But as it does, it lets slip a little
pollutant called a free radical, or oxidant, the same thing that
makes iron rust. Every day countless free radicals are let loose in
the cell, and they tumble out banging into cell membranes, pro-
teins and, crucially, the cell s DNA, doing a little damage as they
do. Some 10,000 free radicals strike the cell s DNA every day.
Some are intercepted by antioxidant chemicals, and when they
do get through, the DNA manages to repair itself with special
proteins. Eventually however, some scientists think, the DNA s
ability to fend off radicals and repair the damage becomes
impaired. Sensing damage, the cell self-destructs, and so the
ageing process gallops on.
So what if we used antioxidants  that is, chemicals that
mopped up free radicals  to slow the process? It s certainly
worked in experiments on fruit flies and rats. But there s no
evidence, yet, that it will work in humans. Vitamins C and E are
antioxidants, but there seems no proof that vitamin supplements
will make much difference. For one thing, your body can absorb
only so much of these vitamins; and for another, you get most
101 FACTS YOU SHOULD KNOW ABOUT FOOD " 183
of the basic antioxidants you need from your normal diet. It may
be that there are antioxidant drugs you can take to boost your
defences against free radicals, but no one yet knows what they
are, or what their effects might be.
No one really knows whether eating food rich in antioxidants
will help defend against the damage done by free radicals in
your body cells  or even if it s worth defending against. But it
certainly can t do any harm to eat more of the fruit and
vegetables that are rich in antioxidants.
" Fruit: raspberries, strawberries, red grapes, oranges, plums,
cherries, blueberries, kiwis, pink grapefruit, raisins, prunes
" Vegetables: corn, onions, red peppers, spinach, aubergine,
sprouts, kale, broccoli, beetroot, alfalfa sprouts
184 " 101 FACTS YOU SHOULD KNOW ABOUT FOOD
99. The Glycaemic Index may give a better idea
of how fattening a food is than calories alone
he Glycaemic Index, or GI, is a measure of how fast the carbo-
Thydrates that food contains are broken down and affect
levels of glucose (sugar) in the blood. Pure glucose is given a GI
of 100, and all other carbohydrates are compared with this. A
food with a GI of under 55 has a low GI. Food low in GI tends
to keep us feeling fuller for longer, helping to keep weight down.
It also contributes less than high-GI food to heart disease and
helps keep diabetes under control. GI labelling is widely used in
Australia, and is being seen increasingly in other countries too.
The more processed a food is, the higher its GI tends to be,
because, in effect, the processing partly digests the carbo-
hydrate, making it easy for the body to finish the job and convert
it into blood sugar. Breakfast cereals like cornflakes, for instance,
have a high GI. In the same way, cooking can increase the GI of
food, which is why long-baked potatoes have a higher GI than just
boiled new potatoes. Fibre, however, tends to lower GI because
it slows digestion down.
GI labelling can be misleading, though, to how fattening a
food is  because it takes no account of just how rich in calories
a food is. Crisps, for instance, have a relatively low GI of around
54, but the fat used to fry them is so rich in calories that they
are actually a fattening food.
101 FACTS YOU SHOULD KNOW ABOUT FOOD " 185
Lower-GI food Higher-GI food
Breakfast cereals
Porridge Cornflakes
Sugar-free muesli Sweetened muesli
Breads
Granary White bread
Rye bread Brown bread [ Pobierz całość w formacie PDF ]

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