Guide to Fats
At one time we knew very little about fat except
that it made foods taste better. We cooked our food using lard or
shortening. We spread butter on our toast and plopped
sour cream on our baked potatoes. Farmers bred their animals to
produce milk with high butterfat content and meat "marbled" with
fat because that was what most people wanted to eat.
But ever since word got out that diets high in fat are related
to heart disease, things have become more complicated. Experts tell
us there are several different kinds of fat, some of them worse for
our health than others. In addition to saturated, monounsaturated and
polyunsaturated fats, there are triglycerides, trans fatty acids,
and omega 3 and omega 6 fatty acids. Most people have learned
something about cholesterol, and many 
of us have been to the doctor for a blood test to learn our
cholesterol "number." Now, however, it turns out that there's more
than one kind of cholesterol, too.
Almost every day there are newspaper reports of new studies
or recommendations about what to eat or what not to eat: Lard is
bad, olive oil is good, margarine is better for you than butter--
then again, maybe it's not.
Amid the welter of confusing terms and conflicting details,
consumers are often baffled about how to improve their diets.
FDA recently issued new regulations that will enable consumers
to see clearly on a food product's label how much and what kind of
fat the product contains. (See "A Little Lite Reading" in the
June 1993 FDA Consumer.) Understanding the terms used to discuss
fat is crucial if you want to make sure your diet is within
recommended guidelines (see accompanying article).
Fats and Fatty Acids
Fats are a group of chemical compounds that contain fatty
acids. Energy is stored in the body mostly in the form of fat. Fat
is needed in the diet to supply essential fatty acids, substances
essential for growth but not produced by the body itself.
There are three main types of fatty acids: saturated,
monounsaturated and polyunsaturated. All fatty acids are molecules
composed mostly of carbon and hydrogen atoms. A saturated fatty
acid has the maximum possible number of hydrogen atoms attached to
every carbon atom. It is therefore said to be "saturated" with
hydrogen atoms.
Some fatty acids are missing one pair of hydrogen atoms in the
middle of the molecule. This gap is called an "unsaturation" and
the fatty acid is said to be "monounsaturated" because it has one
gap. Fatty acids that are missing more than one pair of hydrogen
atoms are called "polyunsaturated."
Saturated fats (which contain saturated fatty acids) are
mostly found in foods of animal origin. Monounsaturated and
polyunsaturated fats (which contain monounsaturated and
polyunsaturated fatty acids) are mostly found in foods of plant
origin and some seafoods. Polyunsaturated fatty acids are of two
kinds, omega-3 or omega-6. Scientists tell them apart by where in
the molecule the "unsaturations," or missing hydrogen atoms, occur.
Recently a new term has been added to the fat lexicon: trans
fatty acids. These are byproducts of partial hydrogenation, a
process in which some of the missing hydrogen atoms are put back
into polyunsaturated fats. "Partially hydrogenated vegetable oils,"
such as vegetable shortening and margarine, are solid at room
temperature.
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