Free The World Turned Upside Down: The Second Low-Carbohydrate Revolution by Richard David Feinman

plow
ahead and
look up stuff that is the hardest. You'll usually get another chance on
the
chemistry.
    First, you need to know that the term lipids refers to a diverse collection of
chemical compounds that have in common that they are sparingly or not
at all
soluble in water. The group includes fatty acids, fats and oils,
cholesterol
and derivatives of these compounds. Directly applicable here are the
fats and
oils and their constituent components, the fatty acids and glycerol.
We'll look
at fat structure and the meaning of "saturated" and "unsaturated" fat.
I'll
describe the idea of a lipoprotein, the cholesterol-containing
particles, LDL
and HDL that are in your lipid work-up. We'll touch on the diet-heart
hypothesis and the original idea of the Mediterranean Diet. The big
payoff will
be to understand how fat interacts with carbohydrate and, looking
ahead, we
will try to understand how, as we all know too well, carbohydrates can
be
converted to fat but, to a large extent, fat cannot be converted to
glucose. We
will want to understand how it is that we cannot use our fat stores to
keep
glucose at normal levels and how it is that the amount of dietary
carbohydrate
may be more important than the amount of dietary fat in determining how
much
body fat we have.

     
     

Chapter 3
    Answers
2.
Introduction to lipid Chemistry.
    Back to the quiz
    8.       A
good source of monounsaturated fat is:
    _____ Butter
    __ X _
Canola Oil
    _____ Corn Oil
    _____ Flaxseed Oil
    __ X __
Olive Oil
    __ X __
Avocado Oil
    _____ Soybean Oil

    Figure
3-1 Composition of common fats and oils. MUFA
= monounsaturated
fatty acids. PUFA = polyunsaturated fatty acids.
    You hear the terms, "saturated fat"
and
"polyunsaturated fat"
often which are not quite precise; only fatty acids can be unsaturated
or
saturated. All dietary and body fats and oils are triglycerides
(TG) , or, more correctly, triacyl
glycerols (TAG) .
The name tells you about the structure: There are three acyl groups
(pronounced
"ay-seal," ay as in hay). Acyl is the adjective form of acid and the
components
are fatty acids and the three acyl groups are attached to the compound glycerol .
It is only the fatty acids
that can be saturated (SFA) or unsaturated (UFA). "Saturated fat" means
that
the fat contains a higher proportion of saturated fatty acids.
Similarly for
unsaturated and its variations, mono- (MUFA), or poly- (PUFA).
    Fats have an E-shaped structure. The
arms
of the E are the fatty
acids and the backbone is the compound glycerol. ( Figure
3-2 ). The chemical bond that
attaches the fatty acid to the glycerol is called an ester
bond . You only need to know the
term ester because when the fatty acids are found alone, especially in
blood,
they are referred to as free
fatty acids (FFA) o r, because they are no
longer attached to the
glycerol part by the ester bonds, non-esterified fatty acids (NEFA) :
FFA and NEFA are the
same thing . Fatty acids are long chains of carbon atoms with a carboxylic acid
group. The
fatty acids provide the real fuel in fat in the long hydrocarbon
chains, like
gasoline. Fatty acid comprise the arms of the "E." Carbon-carbon double
bonds
are more chemically reactive and can be converted to single bonds, e.g.
with
hydrogen atoms in which case they are called saturated, that is
saturated with
hydrogen. "Saturated" means that all the carbon-carbon chemical bonds
are
single bonds.

    Figure
3-2 . Fat structure. Fats and oils are
triglycerides (TG),
formally triacylglycerol (TAG). There are 3 ester bonds to glycerol.
    "Saturated fats," again, have a large
number of SFAs in the arms
of the E structure. Similarly, "unsaturated fats" have high amounts
MUFA
(monounsaturated fatty acids) and PUFA (polyunsaturated fatty acids).
For some
fats, however, it is not clear that these terms are useful. One thinks
of lard
as a kind of pure high saturated fat but it is only 41 % saturated,
while it is
mostly (47 %) MUFA, predominantly oleic acid, the main fat