FATTY ACIDS
F
of excess fat include cancers of the
breast, colon, and prostate and type
2
diabetes mellitus
.
USES IN THE BODY
Some dietary fats, mainly triglycerides
(combinations of glycerol and three
fatty acids), are sources of the fat-solu-
ble vitamins A, D, E, and K and also of
essential fatty acids.
Triglycerides are the main form of
fat stored in the body. These stores act
as an energy reserve; they also provide
insulation and a protective layer for
delicate organs such as the heart and
kidneys.
Phospholipids
are
structural
fats found in cell membranes. Sterols,
such as
cholesterol
,
are found in animal
and plant tissues; they have a variety of
functions, and are essential for making
hormones or vitamins. Phospholipids
and sterols are made in the body from
nutrients provided in the diet.
FAT METABOLISM
Dietary fats are first emulsified
(re-
duced to m icroscopic particles) by
bile
salts before being broken down by
lipase, a pancreatic
enzyme
.
They are
absorbed via the
lymphatic system
be-
fore entering the bloodstream.
To be carried in the blood, the lipids
become
bound to
proteins;
in
this
state, they are known as lipoproteins.
There are four classes of lipoprotein:
chylomicrons;
high-density
lipopro-
teins (HDLs); low-density lipoproteins
(LDLs); and very low-density lipopro-
teins (VLDLs). LDLs and VLDLs contain
large amounts of cholesterol, w hich
they carry through the bloodstream
and deposit in tissues; they are some-
times referred to as bad fats. HDLs,
known as good fats, pick up choles-
terol and carry it back to the liver for
processing and excretion. High levels
of LDLs are associated w ith athero-
sclerosis,
whereas
HDLs
have
a
protective effect. (See also
nutrition
. )
fatty acids
Organic acids, containing carbon, oxy-
gen,
and
hydrogen,
that
are
con-
stituents of
fats and
oils.There are more
than 40 fatty acids found in nature;
they are distinguished from one anoth-
er by their constituent numbers of
carbon and hydrogen atoms.
Certain fatty acids cannot be syn-
thesized by the body and must be
provided by the diet. These substances,
sometimes collectively termed essen-
tial fatty acids, are linoleic, linolenic,
and arachidonic acids. Strictly speak-
ing, only linoleic acid is truly essential,
because the body can make the other
two from linoleic acid obtained from
food. (See also
nutrition.
)
fatty degeneration
A general term describing the accumu-
lation of fat w ithin the cells of tissues
damaged by disease.
fatty diarrhoea
See
steatorrhoea
.
fatty liver
A condition in w hich fat accumulates
within the liver cells. The most common
cause of fatty liver is excessive consump-
tion of alcohol which, if continued,
eventually leads to
cirrhosis
.
However, if
the drinking of alcohol stops, the fat
clears from the liver. Fatty liver can also
occur in association with
obesity, dia-
betes mellitus
,
starvation, and in some
cases of chronic ill-health.
favism
A disorder that is characterized by an
extreme sensitivity to the broad bean
V
ic ia fa b a
(fava bean). If an affected per-
son eats these beans, a chemical in the
bean causes rapid destruction of red
blood cells, leading to a severe type of
anaemia (see
anaemia, haemolytic
) .
Favism is uncommon except in some
areas of the Mediterranean. It is a sex-
linked
genetic disorder
.
Affected people
have
G
6 PD deficiency
,
a defect in a cer-
tain
chemical pathway
in
their
red
blood cells that normally helps protect
the cells from injury.
Children with a family history of
favism can be screened for the disorder
at an early age. If the condition is
found, they must avoid fava beans as
well as certain drugs, including some
antimalarial drugs
and
antibiotic drugs,
that can have a sim ilar effect on their
red blood cells.
febrile
Feverish or related to
fever
.
Febrile con-
vulsions, for example, occur mainly in
young children with high tempera-
tures (see
convulsion, febrile
) .
febrile convulsion
See
convulsion
,
febrile
.
feedback
A self-regulating mechanism that con-
trols certain body processes, such as
hormone and enzyme production.
If, for example, levels of a hormone are
too high, output of any substance that
stimulates
the
horm one’s
release
is
inhibited; the result is reduced hor-
mone production (negative feedback).
The reverse process (positive feedback)
restores the balance if the levels of a
hormone become too low. (See also
endocrine system
.)
feeding, artificial
The administration of nutrients other
than by mouth, usually by way of a
tube passed through the nose into the
stomach or small intestine. If long-
term artificial feeding is anticipated, a
tube is inserted directly into the stom-
ach or upper small intestine during
endoscopic surgery (see
gastroscopy
).
This is called
enteral feeding
.
If the gas-
trointestinal tract is not functioning,
nutrients must be introduced directly
into
the
bloodstream
(see
infusion,
intravenous
) .
This type of feeding is
known as
parenteral nutrition
.
TUBE FEEDING
Tube feeding
may be necessary for
people who have difficulty swallow-
ing, or gastrointestinal disorders (for
example, conditions resulting in
malab-
sorption
),
or
disorders
affecting
the
nervous system or kidneys. Premature
babies often require tube feeding if
their
suckling reflexes
are undeveloped,
as do critically ill patients due to their
increased nutritional requirements.
Food mixtures,
or preparations of
nutrients, are given through a tube that
is passed through the patient’s nostril
and down to the stomach or duode-
num.There are two methods of feeding:
continuous
drip
feeding,
and
bolus
feeding (in w hich set amounts of nutri-
ents
are
given
at
regular
intervals
throughout the day). In both methods,
the rate of delivery of the food can be
controlled by a pump.
INTRAVENOUS FEEDING
Intravenous
feeding is usually
given
when large areas of the small intestine
have been damaged by disease or have
been surgically removed. Nutrient prep-
arations are given and are inserted into
a large central vein near the heart, via a
catheter
(a thin, flexible tube) that is
buried under the skin.
feeding, infant
A person grows more rapidly in his or
her first year than at any other time in
life. A good diet is essential for healthy
growth and development.
300
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