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1995-03-13
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VegSocUK Information Sheet
THE VEGETARIAN SOCIETY
___________________________________
FATS & CHOLESTEROL
Fats provide a concentrated source of energy in the diet. The building
blocks of fats are called fatty acids. These can be either saturated,
monounsaturated or poly-unsaturated. Foods rich in saturated fats are
usually of animal origin. Vegetable fats are generally unsaturated.
Saturated fat raises the level of cholesterol in the blood. Cholesterol is
present in animal foods but not plant foods. It is essential for metabolism
but is not needed in the diet as our bodies can produce all that is needed.
Raised blood cholesterol is associated with an increased risk of heart
disease.
Fats and oils are essentially the same. Fats tend to be solid at room
temperature whilst oils are liquid. The term lipids include both fats and
oils.
___________________________________
STRUCTURE & FUNCTIONS
Fats consist of fatty acids and glycerol. Nearly all the fats in our bodies
and in foods are triglycerides, being made up of three fatty acid molecules
to one glycerol molecule. There are about 16 di fferent fatty acids commonly
present in foods. The nature of fat depends on its constituent fatty acids.
Fats can be classed as either saturated, monounsaturated or polyunsaturated.
This depends on the type of chemical bonds present in the fatty acid. If a
fatty acid has all the hydrogen atoms it can ho ld it is termed saturated.
However, if some of the hydrogen atoms are absent and the usual single bond
between carbon atoms has been replaced by a double bond, then it is
unsaturated. If there is just one double bond then it is monounsaturated. If
there is more than one then it is polyunsaturated. Most fats contain a
proportion of each of these three basic types of fatty acid but are
generally described according to which type predominates.
Saturated fats tend to be animal fats and are solid at room temperature.
Butter, lard, suet and meat fat are saturated fats. Unsaturated fats are
liquid at room temperature. They are usually of plant origin, though fish
oils may also be high in polyunsaturated fatty acids. Plant oils may be
hardened by the addition of hydrogen atoms, converting double bonds to single
bonds. This process is known as hydrogenation. Hydrogenated vegetable oils
are often present in margarine and other processed foods.
Fats have a number of important functions in the body. As well as being a
concentrated source of energy, fats act as carriers for fat-soluble vitamins
A, D, E and K. Fats are also essential for the structure of cell membranes
and are precursors of many hormones.
___________________________________
ESSENTIAL FATTY ACIDS
Two fatty acids are termed essential fatty acids. These are linoleic
acid and a-linolenic acid. These must be present in the diet as the body
is unable to make them itself. They are widely present in plant oils
such as sunflower, rapeseed and soyabean oils.
Linoleic acid is converted into the body to arachidonic acid from which
prostoglandins and other vital compounds are made. Because of this
conversion, arachidonic acid is not an essential fatty acid as was once
believed. a-Linolenic acid is converted to eicosapentanoic acid (EPA) which
is important in proper nerve function. EPA is present in fish oils and is
claimed to be beneficial in reducing the symptoms of arthri tis and the risk
of heart disease. For this reason, fish oils are sometimes used
therapeutically. Plant oils containing large amounts of a-linolenic acid
can be used as an alternative by vegetarians. Linseeds and linseed oil
are particularly rich sources of a-linolenic acid.
___________________________________
CHOLESTEROL
Cholesterol belongs to the sterol group of fats. It is present in all animal
tissues but is absent from plants. Cholesterol is essential as a component of
cell membranes and a precursor of bile acids and certain hormones. The body
can make its own cholesterol and so a dietary source is not required.
Cholesterol is transported in to various proteins. These complex molecules
are called lipoproteins. There are four main types of lipoprotein involved in
cholesterol transport. The most commonly refer red to are low density
lipoprotein (LDL) and high density lipoprotein (HDL).
Cholesterol may form plaques on artery walls if levels in the blood are too
high. This can lead to atherosclerosis. Because of this high blood
cholesterol is linked with heart disease. It is the LDL cholesterol which
has been linked to heart disease. HDL cholesterol may help protect against
the risk of heart disease.
The amount of dietary cholesterol is not clearly linked to levels of
cholesterol in the blood. Blood cholesterol is more closely related to the
amount of saturated fat in the diet, saturated fat raising blood
cholesterol. Unsaturated fats are not thought to raise blood
cholesterol and may indeed lower levels.
___________________________________
TRANS FATTY ACIDS
Unsaturated fatty acids can exist in two different geometric forms.
These are called the cis and trans forms. Unsaturated fatty acids exist
naturally in the cis form. During food manufacturing processes these
cis fatty acids may be changed to trans fatty acids. Hydrogenation of
margarine causes this to occur. It has been suggested that trans fatty
acids can increase the risk of heart disease.
___________________________________
FREE RADICALS
Free radicals are highly reactive molecules which have been linked to both
heart disease and cancer. A number of factors, including alcohol, stress and
environmental pollutants can increase the generation of free radicals in the
body. Polyunsaturated fats can also generate free radicals, especially when
exposed to heat or sunlight. Because of this it is suggested that vegetable
oils should be stored out of direct sunlight. Mono-unsaturated olive oil is
less vulnerable to free radical generation and so is a better choice for
frying.
Anti-oxidants such as vitamins A, C and E offer protection against free
radicals. Fresh fruit and vegetables are rich in these anti-oxidants.
___________________________________
DIETARY SOURCES
Saturated fats are nearly always from animal foods. Meat, eggs and dairy
products all contain saturated fats. Lard and suet are saturated fats.
Coconut oil and palm oil are vegetable sources of saturated fats. Olive oil
is a monounsaturated fat. Polyunsaturated fats are usually from plant
sources.
The ratio of polyunsaturated to saturated fats in the diet is often called
the P:S ratio.
Cholesterol is present in all animal foods but not plant foods. Egg yolks
and high-fat dairy products are high in cholesterol.
___________________________________
REQUIRED INTAKES
Currently it is believed that around 42% of energy in the typical British
diet is from fat. Dietary advice is to reduce this. The COMA (Committee on
Medical Aspects of Food Policy) report advocated t hat no more than 35% of
daily energy requirement should come from fat whilst the NACNE (National
Advisory Committee on Nutritional Education) paper recommends a reduction to
no more than 30%. Special emphasis is placed on reducing the a mount of
saturated fat in the diet.
Vegetarian diets tend to be lower in fat than omnivore diets. However,
vegetarians consuming dairy products and processed foods high in fat may
still be consuming too much. Advice to vegetarians is t o keep fat intake
to a minimum, avoid high fat dairy products and processed foods containing
dairy fats and hydrogenated vegetable fats, and to use olive oil for
cooking purposes.
___________________________________
//
This article is copyright to the Vegetarian Society (UK), but may be freely
copied for non-commercial use provided it is kept intact, not altered
and these lines are included.
For futher information contact: The Vegetarian Society, Parkdale, Dunham Road,
Altrincham, Cheshire WA14 4QG, England. Tel: (England) 061 928 0793
email: vegsoc@vegsoc.demon.co.uk
//
[The text of this file was obtained from the Vegetarian Society (UK) in
March 1995.]