fats and oilsNutrients that provide the
body with its most concentrated form
of energy. Fats, which are also called
lipids, are compounds containing chains
of carbon and hydrogen with very little
oxygen. Chemically, fats consist mostly
of fatty acidscombined with glycerol.
They are divided into 2 main groups,
saturated and unsaturated, depending
on the proportion of hydrogen atoms. If
the fatty acids contain the maximum
possible quantity of hydrogen, the fats
are saturated. If some sites on the car-
bon chain are unoccupied by hydrogen,
they are unsaturated; when many sites
are vacant, they are polyunsaturated.
Monounsaturated fats are unsaturated
fats with only one site that could take
an extra hydrogen. Animal fats, such as
those in meat and dairy products, are
largely saturated, whereas vegetable fats
tend to be unsaturated.
Fats are usually solid at room temper-
ature; oils are liquid. The amount and
types of fat in the diet have important
implications for health. A diet contain-
ing a large amount of fat, particularly
saturated fat, is linked to an increased
risk of atherosclerosisand subsequent
heart disease and stroke.
Some dietary fats, mainly triglycerides
(combinations of glycerol and 3 fatty
acids), are sources of the fat-soluble
vitamins A, D, E, and K and of essential
fatty acids. Triglycerides are the main
form of fat stored in the body. These
stores act as an energy reserve and also
provide insulation and a protective layer
for delicate organs. 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, often being con-
verted into hormones or vitamins.
Dietary fats are first emulsified by
bile salts before being broken down
by lipase, a pancreatic enzyme. They are
absorbed via the lymphatic system be-
fore entering the bloodstream.
Lipids are carried in the blood bound
to protein; in this state they are known
as lipoproteins. There are 4 classes of
lipoprotein: very low-density lipoproteins
(VLDLs), low-density lipoproteins (LDLs),
high-density lipoproteins (HDLs), and
chylomicrons. LDLs and VLDLs contain
large amounts of cholesterol, which
they carry through the bloodstream and
deposit in tissues. HDLs pick up choles-
terol and carry it back to the liver for
processing and excretion. High levels of
LDLs are associated with atheroscler-
osis, whereas HDLs have a protective
effect. (See also nutrition.)
fatty acidsOrganic acids, containing
carbon, hydrogen, and oxygen, that are
constituents of fats and oils. There
are more than 40 fatty acids, which are
found in nature and which are distin-
guished by their constituent number of
carbon and hydrogen atoms.
Certain fatty acids cannot be synthe-
sized by the body and must be provided
by the diet. These are linoleic, linolenic,
and arachidonic acids, sometimes col-
lectively termed essential fatty acids.
Strictly speaking, only linoleic acid is
essential, since the body can make the
other 2 from linoleic acid obtained from
food. (See also nutrition.)
favismA disorder characterized by an
extreme sensitivity to the broad bean
VICIA FABA(fava). If an affected person
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. The dis-
order is caused by a sex-linked genetic
disorder. Affected people have G6PD
deficiency, a defect in a chemical path-
way in their red cells that normally
helps protect the cells from injury.
Children with a family history of fav-
ism can be screened for the disorder at
an early age. If it is found, they must
avoid fava beans and certain drugs,
including some antimalarial drugsand
antibiotic drugs,that can have a similar
effect on their red blood cells.
febrileFeverish or related to fever, as
in febrile convulsions.
febrile convulsionSee convulsion,
febrile.
feedbackA self-regulating mechanism
that controls certain body processes
such as hormone and enzyme produc-
tion. If, for example, levels of a hormone
are too high, output of any substanceFATS AND OILS FEEDBACK
F