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Below is an excerpt from
Part Two of
The 2004 Multi-Diet
by Anderson A. Anonymous, M.D., Ph.D.
Carbohydrate Quality:
The Glycemic Index
As we discussed in More On… Energy Metabolism & Storage, your digestive
system converts carbohydrate to glucose—which enters the bloodstream almost
immediately. However, when a large amount of glucose suddenly shows up in the
blood, your body must release a large amount of insulin to deal with it. From the
dieter’s point of view large amounts of insulin cause several negative things to
happen, i.e. none of them are much good for losing fat.
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A sudden large amount of insulin entering the blood may overcompensate for the
amount of glucose it is supposed to deal with. This causes an unpleasant state
called “reactive hypoglycemia” . If it happens, blood glucose levels are
forced below normal for a period of time. During this time various organs (mainly
the brain and nervous system) will get less glucose than they want. They then
tend to “wake The Beast” to stimulate you to go eat to get them some more
glucose. (This is not good, since The Beast will probably want you to eat a few
slices of some “low-calorie” food like pizza or chocolate cheesecake.J)
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Insulin tells fat cells to stop releasing fat into the bloodstream to be
burned for fuel by other cells (not good).
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It also tells the fat cells to pick up and store any fat that may enter the
blood along with the carbohydrate you eat, rather than releasing it for other
cells to use for fuel (not good).
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It tells muscles and other tissues that are already burning fat to switch over
to burning glucose instead (not good).
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It tells the liver and muscle cells to start converting glucose to glycogen
for storage (not so bad).
But when glycogen stores are full (and possibly before), it tells the liver and
fat cells to start converting the glucose into FAT (very bad).
Since all of these insulin effects make it harder to lose fat, we would obviously
like to prevent those “large amounts of glucose” from stimulating release of
those “large amounts of insulin”. How can this be done?
Obviously, eating almost no carbohydrate would be one way to avoid these problems—but
under normal circumstances it’s not very practical. Fortunately, it’s also not
necessary. Eating the right type of carbohydrate in more or less normal amounts has a
much more balanced effect on your blood chemistry and a much less disruptive effect
on your life. Specifically, the right types of carbohydrate are digested and absorbed
very slo-o-o-w-ly into the bloodstream. They therefore do not cause that large rise
in blood sugar followed by that correspondingly large insulin response. This “speed
of absorption” is measured by…
The Glycemic Index
The glycemic index (G.I.) is a numerical measurement of how fast the digestive
system converts the carbohydrate in a particular food into glucose and gets it into
the bloodstream. Higher G.I.s mean faster absorption and may cause reactive
hypoglycemia. Lower G.I.s mean slower absorption and probably won’t.
The glycemic index measures the magnitude and duration of the increase in blood
glucose level (bG) after a given type of food is eaten. To determine this, volunteers
eat a specific food in an amount that is known to contain 50 grams of available
carbohydrate. Their blood glucose levels are measured for the next three hours. From
these measurements, the effect of that particular food on blood glucose is calculated
and expressed as a single number—the glycemic index.
The glycemic index compares the effect on blood glucose of eating that particular
food to the effect of eating the same amount of pure glucose (the reference
standard). For example, the G.I. of navy beans is about 40. This means that it raises
blood glucose (bG) only about 40% as much as the same amount of pure glucose would
(this is a relatively low glycemic index). (Note: White bread is also often used as a
reference standard because it’s easier to test. It gives different absolute G.I.
numbers but the same relative rankings among foods—which is what’s important.)
There are some foods whose glycemic index will probably never be measured. For
example, in order to get 50g of carbohydrate from Celery some poor volunteer would
have to eat about 35 eight-inch stalks of it. And when you consider the testing
protocol says that the same person has to do this three times…Yuck! (Maybe if you
pay me 500, no, make that 1000 bucks each time… )
The glycemic index technique is used in diabetes medicine where it was developed
as a tool to help diabetics control blood sugar. However, even in diabetes medicine,
the glycemic index is a relatively new measurement only just now gaining mainstream
acceptance. Canadian professor of nutrition David Jenkins first proposed it in 1981 (“only”
about 20 years agoJ). Since then the concept has proven to give predictable and
reproducible results. Previously, scientists had simply assumed that “complex
carbohydrates” were absorbed slowly and caused only moderate blood glucose rises
(this is often wrong) and that “simple sugars” were absorbed rapidly and caused
sudden rises (also often wrong). The glycemic index technique replaces these
assumptions with actual measurements—almost always a more accurate way to discover
the truth.J
Glycemic Index Tables
About 600 different foods (or varieties of foods) have been tested to determine
their glycemic indices. The results of these tests have been summarized into tables.
Most such tables are based on a reference standard of either glucose or white bread.
The Multi-Diet Glycemic Index Chart uses glucose as the standard.
Glycemic index tables must be used with some caution. Many things can cause the
G.I. value of a particular food you are eating to be different from the G.I. value of
the same food when it was tested. The difference is usually minor, but in a few cases
it can be significant. Rice is an example. Rice contains two types of carbohydrate
(as starch)—amylose (which has a low G.I.) and amylopectin (which has a high G.I.).
Rice varieties that have more amylose have lower G.I.s, and varieties that have more
amylopectin have higher G.I.s. Rice, depending on the variety, can be high or low in
either type and consequently the rice you may be eating may have a high or low G.I.
regardless of what a particular G.I. table says.
The rate of glucose absorption of a particular serving of food can be influenced
by lots of other things also, including: the method of food-processing used, the
method of cooking, ripeness, amounts of protein and fat in the meal, type and length
of storage, and your individual biochemistry. But these other things being equal, you
will always have a greater glucose/insulin response to a high-GI food than to a
low-GI food by approximately the amount suggested by the glycemic index of the food.
Note: Diabetics and others who wish to understand the current state of the art in
glycemic index research by one of its leading proponents should read The G. I.
Factor: The Glycaemic Index Solution by Prof. Janette C. Brand Miller.
Other G.I. Considerations
- Low-GI foods have been shown in tests to reduce hunger (produce greater
satiety).
- Low-G.I. foods tend to enhance endurance time while high-G.I. foods tend to
speed replenishment of muscle glycogen after exercise.
- Glucose is not the only substance that creates an insulin response. Protein
also has this effect, but it’s much smaller. (So protein is a low-G.I. food.)
- The G.I. of processed foods tends to vary less than the G.I. of raw
agricultural produce because of standardized processing techniques. But processed
foods are also to have a higher G.I. than the raw foods. This appears to happen
because higher heats and pressures of commercial food processing techniques make
carbohydrate more “digestible”, (which in this case just means it turns into
glucose quicker).
The Multi-Diet Glycemic Index Chart
The Multi-Diet Glycemic Index Chart shows the foods with known G.I.s that are most
useful to dieters.
It also shows the range of variability in the G.I. of each food. For example,
carrots have a G.I. of 71±22. This means the carrots you get at the store might have
a G.I. of 49 (fairly low), or a G.I. of 93 (almost the same as glucose itself!), or a
G.I. anywhere in between.
A “high” G.I. is usually considered to be any G.I. over one-half (½) the
value of glucose. This is about 50 on the glucose standard (about 70 on the white
bread standard).
We Multi-Dieters can still eat high-G.I. foods of course, but the rule-of-thumb
for them is: The higher the G.I., the less of it you should eat at any one time!
It’s for this reason that I tend to recommend popcorn as a good food for “munchie”
type situations. Popcorn does have a high G.I. But since it’s mostly air and has
very little actual carbohydrate for a given volume, it seems like a lot and can keep
you occupied for a while longer than other foods.(Try a very short “spritz” of
one of those cooking sprays on it to hold the salt—the extra Calories are
completely insignificant.)
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