The structure of a saturated, an unsaturated, and a
trans
unsaturated chemical bond is depicted in
Table 12
and in
Figure 14
.
H
H
|^
|
- C
- C–
|
|
H
H
H
H
|
|
- C =
C –
H
|
- C =
C –
|
H
Saturated Fat Carbon-Carbon
Single-bond hydrogens
Cis
Fat
Carbon-Carbon
Double-bond hydrogens on
same side
Trans
Fat
Carbon-Carbon
Double-bond hydrogens on
opposite sides
Table 12. Depiction of saturated,
cis
-unsaturated, and
trans-
unsaturated fats. RED hydrogens are on the same side of a
cis
-double
bond and on the opposite sides of a
trans
-double bond.
Cis
-fats are bent. This bending causes the molecule to occupy
more space and become more fluid. This is illustrated in
Figure 14
.
Cis
fat
Trans fat
Figure 14.
Cis
fats are bent.
Trans
fats are generally straight.
Dietary Fat
Fat tastes good to most of us—it makes carbohydrate more
palatable. Fat is also relatively inexpensive.
A small amount of fat is necessary in the diet. Diets that derive more than 30% of their calories from fat are
considered unhealthy, because exces
s dietary fat is associated with
obesity, heart disease, stroke, and some cancers.
Polyunsaturated fats are believed
to be better for health than
saturated or hydrogenated fats. Diets
that derive more than 10% of
their calories from saturated fat are considered unhealthy.
US fat consumption averages about 33% of total calories. Excess fat is much more of a public health problem than too
little.
Requirements
Dietary fat is composed of triglycerides, phospholipids, sterols,
and other lipid-soluble components.
Triglycerides are the major component of dietary fats. Triglycerides consist of a glycerol backbone and three fatty acid
chains, the latter of which are classified as saturated,
cis
monounsaturated,
cis
-polyunsaturated, and
trans
-fatty acids.
Monounsaturated fatty acids, saturated fatty acids, and
cholesterol can be synthesized by the body. They are not essential in the diet.
Two polyunsaturated fatty acids are essential in the diet: linoleic
acid and alpha-linolenic acid.
Eicosapentaenoic acid and docosahexaenoic acid, two fatty acids
derived from the elongation and desatur
ation of alpha-linolenic acid,
are also of nutritional significance. Eicosapentaenoic acid and docosahexaenoic acid can be interconverted.
Nutrition for Sports, Essentials of 77