The World Turned Upside Down: The Second Low-Carbohydrate Revolution (7 page)

BOOK: The World Turned Upside Down: The Second Low-Carbohydrate Revolution
7.01Mb size Format: txt, pdf, ePub
ads

...such diets eliminate many foods
that are important
sources of energy, fiber, vitamins, and minerals and are important in
dietary
palatability.

If "care should be taken to avoid
excess
energy intake," what
would it mean for carbohydrate to be "an important source of energy?"
And, does
anybody think that taking a vitamin pill is the equivalent of injecting
insulin? There is also a subtle switch from "carbohydrate" meaning
macronutrient, to using the term to mean carbohydrate-containing food.
Finally,
I would suggest, as in the future history (see Appendix),
that dietary palatability is
not their area of expertise.

The guidelines from the ADA, as from
other
health agencies are
supposed to be serious but, in fact, have the character of an
infomercial and
the standards are those of selling a product rather than presenting a
scientific case. It seems that we are supposed to just take it. The ADA
is a
private organization but they have public support at least in that they
are
tax-exempt. Their experts are often federally funded as well. Are they
really
free to say whatever they want? This is the kernel of the second
low-carbohydrate revolution.

glycemic Index -
politically correct Low-carb.

7.
     
Glycemic
Index measures the increase in blood sugar over 2 hours (per gram of
carbohydrate-containing food that is ingested) compared to glucose
(=100). For
each food indicate the approximate glycemic index as: H, high (70–100),
M,
Medium (40–70) or L, Low (< 40). You may enter a number if you
think you
know or can figure it out:

__ 70 ___ White bread

__ 50 ___ Whole wheat bread

__ 57 ___ Ice cream (average)

__ 38 ___ Ice cream (premium)

__ 47 ___ Carrots

__ 60 ___ Sucrose (table sugar)

__ 20 ___ Fructose

__ 60 ___ Bran muffin

__ 60 ___ Banana

In Chapter 1, we had proclaimed
Rule 2
,
the rule for losing weight:

If you want to lose weight: Don't
eat. If you have to eat,
don't eat carbs. If you have to eat carbs, eat low-glycemic index carbs.

The value of not eating is obvious
and, by now, you should be
convinced that something about dietary carbohydrate is important for
weight
loss, but is there really anything to the glycemic index? Can it help
you?

The basic idea is that the effect of
carbohydrate on blood
glucose will be determined by other factors than simply how much
carbohydrate
is in a particular food. The glycemic index addresses the old idea,
pretty much
dogma when I was in school, that simple sugars would cause a rapid rise
in
blood glucose, but complex carbohydrate which, at that time, still
meant
polysaccharides (starch), would not. At some point, though, people
asked if
this idea was really true and, it turns out, when you actually measure
the
effect of foods on blood glucose, it's not easily predictable, that is,
must be
determined experimentally. Glycemic Index (GI) is precisely defined as
the area
under the blood glucose time-curve during the first 2 hours after
consumption
of 50 grams of carbohydrate-containing food. In other words, it is
total amount
of blood glucose for a fixed time period after

Intellectually, glycemic index was an
important idea. The
same principle as low-carbohydrate diets, and seemingly of practical
value,
low-GI diets have evolved to be a politically correct form of
carbohydrate
restriction and such diets are recommended as an
alternative
to low-carbohydrate diets.
Insofar as low-GI diets are really helpful, it is that they are simply
a weak
form of carbohydrate restriction and, the point of Rule #2, they are
strictly
secondary to real control of carbohydrate intake. Eric Westman who has
experience with both kinds of diets put it well: "If low-GI is good,
why not
no-GI?"

Figure 2-3.
The glycemic index eating the
food.

GI is mainly influenced by the
absolute concentration of
glucose in the food, the extent to which glucose appears in the blood
(not
necessarily from the food itself) and the quantity of other nutrients
such as
fat or fiber in the carbohydrate-containing food because this may slow
the
digestion or absorption of carbohydrate. GI diets are complicated and
require
looking up and calculating values, a feature which may be appealing to
some,
but is probably annoying to most.

The difference between intensive
variables, like calorie
density (or any density) and extensive variables, like total
carbohydrate eaten,
was brought out at the beginning of the quiz. GI is an intensive
variable. Two
bowls of cereal have the same GI as one. If there is not much
carbohydrate (or
really much glucose) in a food, it will have a low GI but it could have
a large
effect if you consume a lot. The
glycemic
load
attempts to correct this problem. The glycemic load, or GL, is defined
as the
GI multiplied by the grams of carbohydrate in a sample of a particular
food.
Obviously, GL is still an intensive variable. You still have to know
how much
is consumed.

There is also the overall character
of using GI. A slice of
white bread has a high GI. The GI will go down if you smear a
tablespoon of
butter on the bread. It will go down still further if you add two
tablespoons
of butter and, in the limit of infinite buttering, that is, pure
butter, you
will have a GI = 0 which is probably not the intent of those people who
want to
use the GI as a guide to eating.

Overall, low-GI diets may be
preferable to high-GI diets but
there are many ambiguities. One feature that is of interest is that GI
measures
blood
glucose
.
Fructose, a sugar of great current interest (because it is 50 % of
sucrose
(table sugar) or high fructose corn syrup) is partially converted to
glucose in
2 hours which is why the GI of fructose is 20 and not zero. In fact,
more is
converted after that time, severely compromising any assertion about
the
differences in effect of the two sugars. Sucrose has a GI of 70 which
is
roughly the average of glucose and fructose. Thus, ice cream has a
lower GI
than potatoes. But now we can't recommend ice cream because of the high
fructose. Lower GI or lower fructose? How to do both without saying
"low-carbohydrate" out loud? This tangled web is woven out of the
failure to
face scientific fact and must necessarily be unravelled by the
low-carbohydrate
revolution.

Summary so far

How did you do? Some critical things
were not known to most
of our medical students. In summary, whatever you knew before, the
stuff that
you need to know to pursue what I'm doing here is that:

  • Almost
    all of the increase in calories in the
    epidemic of obesity
    and diabetes has been due to a dramatic increase in carbohydrate
    consumption.
    The association between the observed pattern of macronutrient
    consumption and
    official advice to reduce fat and increase carbohydrates may be causal.
    How
    could it be else? It is not, however, a sole cause and the bottom line,
    that
    reducing carbohydrate is the best treatment for diabetes suggests, that
    carbohydrate must have played some role in its origins but this remains
    unknown. It seems sensible to keep carbohydrates low to avoid diabetes
    but this
    is not established. What is established is that the progression of
    culprits,
    saturated fat, red meat, white rice that are daily "proved" by
    epidemiologic
    studies to be causes, can probably be excluded.

The crux of the problem in
controlling the epidemic of
diabetes can be summarized in the following statements:

  • Dietary
    carbohydrates raise blood glucose in
    people with diabetes
    more than other macronutrients.
  • There
    is no biological requirement for
    carbohydrate (for
    anybody).
  • Health
    agencies recommend high carbohydrates
    (more than 40 % of
    total calories).
  • The
    glycemic index (and glycemic load) are a
    weak form of
    low-carb strategy. The logical problems and the limited experimental
    demonstrations of their efficacy make their use questionable as a
    primary
    strategy but may be of some use in that they encourage carbohydrate
    restriction.
  • Calories
    are about processes not substance
    and looking ahead,
    different processes (oxidation in the calorimeter vs. metabolism) make
    different use of the calories. Also, slightly technical but with direct
    application, it's good to pay attention to the difference between
    intensive
    properties like calorie-density and extensive properties like total
    calories.
    When you hear people say that fat is inherently more fattening, you
    know that
    doesn't mean anything.

Where we're going

The second part of the quiz is about
lipids. There's a little
more chemistry. Many terms in the popular media are not used correctly
and a
little precision will help understand the problem. The discussion in
this part
is somewhat technical if you are unfamiliar with organic chemistry.

Branch
poin
t: You can skip to
Chapter 4
"The first low-carb revolution" to
follow the narrative and come back to this later. I recommend: 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 in olive
oil. So it
is a question of whether you think that lard is half full of SFA or
half empty.
Most important, as in the epidemiologic study described in the
Introduction
,
there is no risk for cardiovascular disease associated with consuming
saturated
fat. This has now been borne out by large population studies and there
is
simply no correlation – if anything, the studies show that carbohydrate
is a
greater risk than saturated fat but these kinds of correlations are too
weak to
attribute any role at all to either. More on this as we go along.

Figure 3-3.
Single
and double chemical bonds and common fatty acids

The structure of the different kinds
of
fatty acids are shown in
Figure 3-3
.
The
major monounsaturated fatty acid is oleic acid. Everybody thinks that
monounsaturated fats, those with a high content of MUFA like olive oil
are
protective of cardiovascular disease but it is not so clear-cut.

Few fats have only SFAs. Coconut oil
is the exception but
those are medium chain FA (12-16 carbons). Most naturally occurring
fats have
mixtures of FAs but you can make or isolate from natural sources, a fat
that is
all stearic acid (called tristearin or just stearin). It is not usually
used in
food because it is solid and hard but it is used in manufacturing soap
and
other products.

Saturated fats (again, those with
fairly large number of
SFAs) tend to be solid while those with more unsaturated fatty acids
tend to
be liquid – generally, the more saturation the higher the melting
point. To
understand why, we need to look deeper into the structure of fatty
acids and
the question brings us to the issue of "
trans
-fats."

What are trans-fats? In
fact, what is "trans"?

When vegetable oils are hydrogenated,
the process by which
some of the unsaturated FAs are turned to saturated, a side-reaction
can occur
that changes the configuration of some of the unsaturated fatty acids
from
cis
-
to
trans
-.

Let me explain what "
tran
s"
means since the Nutritional Murphy's Law dictates that confusion will
be
introduced wherever possible. The carbon-carbon double bond has rigid
geometry,
that is, unlike the carbon-carbon single bond, there is no rotation
around the
bond. So, if you imagine a chain of carbon atoms as in a hydrocarbon
like
gasoline or the backbone of a fatty acid, if the bonds are all
saturated
(single) bonds then you can think of the molecule as somewhat floppy
because of
free rotation around the bonds. If there is a double bond in this
chain, there
are now two ways to arrange the structure. The two carbons in a double
bond can
have hydrogen atoms on the same side of the bond (
cis
-)
or on opposite sides (
trans
-).
Figure 3-4
shows
the geometry around double bonds.

Figure 3-4.
Orientation around chemical double bonds. The two carbons in a double
bond each
have a hydrogen atom and another atom, a carbon or
, the case
of FA, carbon
chain. if these are on the same side of the double bond, they have the
cis
-configuration.
Otherwise,
trans
-.

Almost all naturally occurring fatty
acids are have the
cis
configuration but it
is important to understand that, by itself, it is just a designation
about the
millions of double bond-containing compounds in the world.
Figure 3-4
shows that UFAs
have more structure than SFAs
and this is why saturated fats tend to be solid (easier to pack into a
solid;
by analogy, it is easier to pack T-shirts into a box than to pack model
Eiffel
Towers or heads of Nefertiti).

MUFAs and the
Mediterranean Diet.

The Mediterranean Diet is widely
recommended for its health
benefits although the data is pretty weak and it is not obvious that
anybody
knows what the diet is beyond the idea that you have to pour olive oil
on
everything. The idea probably comes from Ancel Keys, generally
considered the
father of lipophobia. Keys originally found a good correlation between
fat
consumption (actually fat availability) in six different countries and
the
incidence of heart disease in those countries
[21]
.
It
wasn't long, however, before the Secretary of Health in New York State
and a
professor at Berkeley published a paper showing that there were data
from
countries other than the six that Keys had studied. Had he used all of
that
data, the correlation would not have looked so good (described in
[22-24]
among others) . Keys has
generally been
characterized as a zealot although he was probably more open-minded
than some
of his followers. He was, however, not easily embarrassed and undertook
a study
of seven countries.

Okay.
Seven
Countries.

The Seven Countries study on dietary
availability of fat had the
interesting result that the two countries with the highest intake of
fat were
Finland, which had the highest incidence of CVD and Crete, which had
the lowest
[25]
. It was deduced that
this had to do with the type
of fat, saturated in the case of Finland and unsaturated, in the case
of Crete.
It was later pointed out that there were large differences in CVD
between
different areas of Finland that had the same diet. This
information was ignored
by Keys who was also a pioneer in this approach to dealing with
conflicting
data. In any case, the finding immediately led to the recommendations
to lower
saturated fat, although for most people there was a lingering idea that
it was
good to reduce fat across the board. Health agencies were quite a bit
stronger
at stepping up the pressure on saturated fat but not so good at
admitting the
error in recommending low-fat. This is still the state of affairs. The
real
problem, however, is that the link between saturated fat and heart
disease has
been impossible to establish; direct tests failed right off and
continue to
fail. The story of the political triumph of an idea that was clearly
contradicted by the science has been told numerous times (e.g.,
references
[11,
22,
23,
26,
27]
)
and yet the phenomenon
still persists. Every time you see a low-fat item in the supermarket
you are
looking at an artifact of one of the most bizarre stories in the
history of
science.

BOOK: The World Turned Upside Down: The Second Low-Carbohydrate Revolution
7.01Mb size Format: txt, pdf, ePub
ads

Other books

Too Jewish by Friedmann, Patty
Spirit Wars by Mon D Rea
The Mare by Mary Gaitskill
These Dark Things by Jan Weiss
The Black Pearl by Scott O'Dell
6 Under The Final Moon by Hannah Jayne
On the Verge by Ariella Papa