Chemical Composition of the Body 37Figure 2.18 Structural
formulas for fatty acids. ( a ) The
formula for saturated fatty acids
and ( b ) the formula for unsaturated
fatty acids. Double bonds, which
are points of unsaturation, are
highlighted in yellow.HHHHHHHHHHHHH(a)
CCCCCCHHHHHHH
Palmitic acid,
a saturated fatty acidHHHCCCCCHHHHHHHHHHCCCCCCOOHHHHHHHHH HH(b)
CCCCCCHHHHHH
Linolenic acid,
an unsaturated fatty acidHCCCCCHHHHHHHHHHCCCCCHHCHHHHCCCOOHFITNESS APPLICATION
The American Heart Association recommends that people
limit the amount of saturated fat they eat to less than 7%, and
the amount of trans fats they eat to less than 1%, of the total
number of calories they consume per day. This is because
both saturated fats and trans fats may raise the total blood
cholesterol levels, which contributes to atherosclerosis
(hardening of the arteries). Trans fats not only raise the level of
LDL cholesterol (the “bad cholesterol” that contributes to ath-
erosclerosis), they also lower the amount of HDL cholesterol
(the “good cholesterol” that helps protect against atheroscle-
rosis). Trans fats additionally raise the plasma triglyceride
levels and have other effects that promote the formation of
plaques in the arteries that are characteristic of atheroscle-
rosis. The Food and Drug Administration (FDA) now requires
that all manufacturers list trans fats on their food labels.
The major food sources of saturated fats are meats
and dairy; for example, beef fat is 52% saturated, and
butter fat is 66% saturated. Trans fats are produced arti-
ficially by partially hydrogenating vegetable oils (this is
how margarine is made), and they are common in fried
and baked foods. In trans fatty acids, the single hydrogen
atoms bonded to each carbon located on either side of
the double bond are located on the opposite (trans) sides
of the molecule ( fig. 2.19 , right), which causes the carbon
atoms to form a straight chain. By contrast, in most natu-
rally occurring fatty acids, the hydrogens are located on
the same, or cis, side ( fig. 2.19 , left), causing the fatty acid
chain to bend at the double bonds and produce a saw-
toothed pattern.Figure 2.19 The structure of cis and trans fatty
acids. Oleic acid is a naturally occurring fatty acid with one
double bond. Notice that both hydrogen atoms (yellow) on the
carbons that share this double bond are on the same side of the
molecule—this is called the cis configuration. The cis configuration
makes this naturally occurring fatty acid bend. The fatty acid on
the right is the same size and also has one double bond, but its
hydrogens here are on opposite sides of the molecule, known as
the trans configuration. This makes the fatty acid stay straight,
more like a saturated fatty acid. Note that only these hydrogens
and the ones on the carboxyl groups ( bottom ) are shown. Those
carbons that are joined by single bonds are also each bonded to
2 hydrogen atoms, but those hydrogens are not illustrated.Oleic Acid Elaidic Acid
Carbon
HydrogenCis double bond Trans double bondOxygen