Here
are brief definitions of the key terms important to an understanding of
the role of fat in the diet.
Cholesterol
A chemical compound
manufactured in the body. It is used to build cell membranes
and brain and nerve tissues. Cholesterol also helps
the body make steroid hormones and bile acids.
Dietary cholesterol
Cholesterol found
in animal products that are part of the human diet.
Egg yolks, liver, meat, some shellfish, and whole-milk
dairy products are all sources of dietary cholesterol.
Fatty acid
A molecule composed
mostly of carbon and hydrogen atoms. Fatty acids are
the building blocks of fats.
Fat
A chemical compound
containing one or more fatty acids. Fat is one of the
three main constituents of food (the others are protein
and carbohydrate). It is also the principal form in
which energy is stored in the body.
Hydrogenated
fat
A fat that has
been chemically altered by the addition of hydrogen
atoms (see trans fatty acid). Vegetable shortening and
margarine are hydrogenated fats.
Lipid
A chemical compound
characterized by the fact that it is insoluble in water.
Both fat and cholesterol are members of the lipid family.
Lipoprotein
A chemical compound
made of fat and protein. Lipoproteins that have more
fat than protein are called low-density lipoproteins
(LDLs). Lipoproteins that have more protein than fat
are called high-density lipoproteins (HDLs). Lipoproteins
are found in the blood, where their main function is
to carry cholesterol.
Monounsaturated
fatty acid
A fatty acid that
is missing one pair of hydrogen atoms in the middle
of the molecule. The gap is called an "unsaturation."
Monounsaturated fatty acids are found mostly in plant
and sea foods. Olive oil and canola oil are high in
monounsaturated fatty acids. Monounsaturated fatty acids
tend to lower levels of LDL-cholesterol in the blood.
Polyunsaturated
fatty acid
A fatty acid that
is missing more than one pair of hydrogen atoms. Polyunsaturated
fatty acids are mostly found in plant and sea foods.
Safflower oil and corn oil are high in polyunsaturated
fatty acids. Polyunsaturated fatty acids tend to lower
levels of both HDL-cholesterol and LDL-cholesterol in
the blood.
Saturated fatty
acid
A fatty acid that
has the maximum possible number of hydrogen atoms attached
to every carbon atom. It is said to be "saturated" with
hydrogen atoms. Saturated fatty acids are mostly found
in animal products such as meat and whole milk. Butter
and lard are high in saturated fatty acids. Saturated
fatty acids tend to raise levels of LDL-cholesterol
("bad" cholesterol) in the blood. Elevated levels of
LDL-cholesterol are associated with heart disease.
Trans fatty
acid
A polyunsaturated
fatty acid in which some of the missing hydrogen atoms
have been put back in a chemical process called hydrogenation,
resulting in "straighter" fatty acids that solidify
at higher temperatures. Trans fatty acids are under
study to determine their effects on cholesterol.
