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CD-ROM Aktief 1995 #3
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PROTEIN.TXT
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1995-03-13
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VegSocUK Information Sheet
THE VEGETARIAN SOCIETY
___________________________________
PROTEIN
Being vegetarian does not mean your diet will be lacking in protein. Most
plant foods contain protein and in fact it would be very difficult to design
a vegetarian diet that is short on protein. Excess dietary protein may lead
to health problems. It it now thought that one of the benefits of a
vegetarian diet is that it contains adequate but not excessive protein.
Proteins are made up of smaller units called amino acids. There are about 20
different amino acids, eight of which must be present in the diet. These are
the essential amino acids. Unlike animal proteins, plant proteins may not
contain all the essential amino acids in the necessary proportions. However,
a varied vegetarian diet means a mixture of proteins are consumed, the amino
acids in one protein compensating for the deficiencies of another.
STRUCTURE & FUNCTIONS
Proteins are highly complex molecules comprised of linked amino acids. Amino
acids are simple compounds containing carbon, hydrogen, oxygen, nitrogen and
occasionally sulphur. There are about 20 different amino acids commonly found
in plant and animal proteins. Amino acids link together to form chains called
peptides. A typical protein may contain 500 or more amino acids. Each protein
has it's own unique number and sequence of amino acids which determines it's
particular structure and function.
Proteins are broken down into their constituent amino acids during digestion
which are then absorbed and used to make new proteins in the body. Certain
amino acids can be made by the human body. However, the essential amino acids
cannot be made and so they must be supplied in the diet. The eight essential
amino acids required by humans are: leucine, isoleucine, valine, threonine,
methionine, phenylalanine, tryptophan, and lysine. For children, histidine is
also considered to be an essential amino acid.
Proteins are essential for growth and repair. They play a crucial role in
virtually all biological processes in the body. All enzymes are proteins and
are vital for the body's metabolism. Muscle contraction, immune protection,
and the transmission of nerve impulses are all dependent on proteins.
Proteins in skin and bone provide structural support. Many hormones are
proteins. Protein can also provide a source of energy. Generally the body
uses carbohydrate and fat for energy but when there is excess dietary protein
or inadequate dietary fat and carbohydrate, protein is used. Excess protein
may also be converted to fat and stored.
DIETARY SOURCES
Most foods contain at least some protein. Good sources of protein for
vegetarians include nuts and seeds, pulses, soya products (tofu, soya milk
and TVP), cereals (wheat, oats, and rice), free-range eggs and some dairy
products (milk, cheese and yoghurt).
Different foods contain different proteins, each with their own unique amino
acid composition. The proportions of essential amino acids in foods may
differ from the proportions needed by the body to make proteins. The
proportion of each of the essential amino acids in foods containing protein
determines the quality of that protein. Dietary proteins with all the
essential amino acids in the proportions required by the body are said to be
a high quality protein. If the protein is low in one or more of the essential
amino acids the protein is of a lower quality. The amino acid that is in
shortest supply is called the limiting amino acid.
Protein quality is usually defined according to the amino acid pattern of egg
protein, which is regarded as the ideal. As such, it is not surprising that
animal proteins, such as meat, milk and cheese tend to be of a higher protein
quality than plant proteins. This is why plant proteins are sometimes
referred to as low quality proteins. Many plant proteins are low in one of
the essential amino acids. For instance, grains tend to be short of lysine
whilst pulses are short of methionine. This does not mean that vegetarians or
vegans go short on essential amino acids. Combining plant proteins, such as a
grain with a pulse, leads to a high quality protein which is just as good,
and in some cases better, than protein from animal foods. Soya is a high
quality protein on its own which can be regarded as equal to meat protein.
The limiting amino acid tends to be different in different proteins. This
means when two different foods are combined, the amino acids in one protein
can compensate for the one lacking in the other. This is known as protein
complementing. Vegetarians and vegans eating a well-balanced diet based on
grains, pulses, seeds, nuts and vegetables will be consuming a mixture of
proteins that complement one another naturally without requiring any
planning. Beans on toast, cheese or peanut butter sandwich, muesli with milk
(soya or cow's), and rice with peas or beans are all common examples of
protein complementing.
Previously, it has been thought that protein complementing needed to occur
within a single meal. However, it is now known that this is not necessary as
the body keeps a short-term store of the essential amino acids. A
well-balanced vegetarian or vegan will easily supply all the protein and
essential amino acids needed by the body.
Good sources of protein (single servings)
Chick peas (200 g or 7 oz) 16.0 g
Baked beans (225 g or 8 oz) 11.5 g
Tofu (140 g or 5 oz) 10.3 g
Cow's milk (1/2 pint) 9.2 g
Lentils (120 g or 4 1/4 oz) 9.1 g
Soya milk (1/2 pint) 8.2 g
Muesli (60 g or 2 1/4 oz) 7.7 g
Egg, boiled 7.5 g
Peanuts (30 g or 1 oz) 7.3 g
Bread, (2 slices) 7.0 g
Hard cheese (30 g or 1 oz) 6.8 g
Fair Sources
Brown rice (200 g or 7 oz) 4.4 g
Porridge [water] (160g or 6oz) 2.4 g
Potatoes (200g or 7 oz) 2.8 g
Broccoli (100g or 3 1/2 oz) 3.1 g
Poor sources
1 Apple 0.3 g
1 Carrot 0.4 g
Cream, double (20 g or 2/3 oz) 0.3 g
Butter or margarine (7g or 1/4oz) None
Vegetable oil None
Sugar or syrup None
REQUIRED INTAKES
The old Recommended Daily Amounts (RDA's) have now been replaced by the term
Reference Nutrient Intake (RNI). The RNI is the amount of nutrient which is
enough for at least 97% of the population. Research has shown that we do not
need as much protein as previously thought. The recommended amounts of
protein for adults and children has more than halved in the last 20 years.
Reference Nutrient Intakes for Protein, g/day.
Age RNI
0 to 3 months 12.5 g
4 to 6 months 12.7 g
7 to 9 months 13.7 g
10 to 12 months 14.9 g
1 to 3 yrs 14.5 g
4 to 6 yrs 19.7 g
7 to 10 yrs 28.3 g
Men 11 to 14 yrs 42.1 g
Men 15 to 18 yrs 55.2 g
Men 19 to 49 yrs 55.5 g
Men 50 + yrs 53.3 g
Women 11 to 14 yrs 41.2 g
Women 15 to 18 yrs 45.4 g
Women 19 to 49 yrs 45.0 g
Women 50 + yrs 46.5 g
Pregnant women 51.0 g
Breast feeding women 53 to 56 g
Increased protein needs during pregnancy and breast feeding are usually met
simply by the extra calories from more food. Because infants and children are
growing they require more protein than adults (proportional to their body
weight). Children on a balanced diet usually get enough protein as long as
they are getting enough energy (or calories).
RNI values for protein are valid only if energy needs are also met. If energy
needs are not met then dietary protein is used for energy r