The
glycemic index (GI) is back in circulation again! Truth be told, it
never did go away. Since its initial design in 1981, countless research
publications across the globe continue to attest to its efficacy. Inexplicably,
however, the American medical diabetes community has been reluctant
to endorse its application. As a nutrition consultant in a long-standing
private practice based on the use of the glycemic index, I would like
to give an insider’s view of what it is and how well it has worked
for thousands of my patients. In fact, I consider this an obligation
to my colleagues.
The Glycemic Index: What is it? It is a ranking system
of high carbohydrate (CHO) foods based on their acute glycemic impact.
The GI categorizes carbs by their physiologic response rather than by
their chemical composition. Translation: it estimates the postprandial
blood glucose (BG) excursion of the food. Why does it only rank carbohydrates?
Because carbohydrates are the body’s fuel of choice, and, therefore,
have the greatest effect on blood glucose levels after eating. This
concept was first developed by Drs. David Jenkins and Thomas Wolever
while researching the best foods for diabetes control.
The Glycemic Index: How is it measured? Like all research,
there is strict protocol to follow when testing foods for the glycemic
index:
- Plotting a subject’s BG response to 50 grams available CHO of
the test food every 15 minutes for the first hour, and every 30 minutes
for the second hour.
- Plotting that subject’s BG response to 50 grams of pure glucose
or white bread (both are used as reference foods) tested over the same
time frame.
- Repeating this procedure on 2-3 different days.
- Comparing the two emerging curves gives that subject’s response
to the reference food; this is done by dividing the area under the curve
of the test food by the area under the curve of the reference food (x100
to get a percent).
- This comparison becomes one subject’s GI response to the test
food.
- Repeating the above procedure with 8-10 other subjects.
- Calculating the average GI of all subjects.
- The resulting average number is the GI of that particular test food.
The Glycemic Index: What is the controversy? Current
nutrition recommendations from the American Diabetes Association (ADA)
for all persons with diabetes include considering the total amount of
CHO eaten as more important than the source or type. Glycemic index
research from Canada, Australia, the UK and Europe, South Africa, and
Israel (to give a partial list) affirms that the type of CHO does affect
postprandial BG excursions. That is to say, high GI foods cause a rapid
spike in BG levels, while low GI foods release glucose into the bloodstream
more slowly.
Although in 1984, the ADA supported using the glycemic index, it later
rescinded its endorsement. The argument is that there are no apparent
differences in postprandial BG levels when a particular carbohydrate
is consumed within a mixed meal. Research literature provides an extensive
and impressive list of published articles that disputes this criticism.
The Glycemic Index: Does it really work? As an “in
the trenches” dietitian, I have consistently seen for more than
a decade how easily my patients learn to incorporate low GI foods into
their meal plans and how consistently happy (and relieved) they are
with their results.
It is an easy tool to use because most low GI foods are commonly found
in supermarkets. Also, these same low GI foods (whole grain breads,
old fashioned rolled oats, and sweet potatoes, for example) are touted
for other health benefits (heart health, anti-cancer properties, weight
loss, etc.). My patients seem motivated to make the changes they trust
will improve their general health as well as their diabetes. Then, once
they start feeling and seeing and the results of low GI eating –
my diabetic patients test four times a day, including pre- and two-hour-post
prandially - the numbers speak for themselves, and they become committed
to their low GI meal plan.
Frequently, my patients are able to reduce or even eliminate their
diabetes medications, including insulin, once they have learned how
to lower their glycemic response to their carbohydrate intake by opting
for low GI choices. And benefits of low GI foods are not just limited
to diabetic control.
Many patients improve their cardiac profiles by lowering their lipids
and blood pressure. I have found it unbeatable for weight loss too –
one patient lost 195 pounds in two years of low GI eating! Yes, the
glycemic index works, sometimes dramatically!
The Glycemic Index: Does it have a future? The answer
is a resounding “Yes!” The American Diabetes Association
and glycemic index research are moving toward a common ground: glycemic
load. That is to say, that both groups are pointing to the importance
of the total amount of carbohydrate absorbed, the “glycemic load”
(albeit from different perspectives).
ADA explains that by successfully limiting the total amount of carbs
consumed, the glycemic load will be controlled and the resulting BG
level will not spike. GI research ascertains that low GI carbs control
the glycemic load because of how slowly they are absorbed. In addition,
because low GI carbs are more satiating, they are a great tool for limiting
total amount of carbs consumed. Herein converges our current understanding
of carbohydrate metabolism and BG control.
The Glycemic Index: How to start using it? When designing
a meal plan for your patients, choose 45-65% of total calories primarily
from the low or intermediate section of the glycemic index. This is
not to say that high GI foods should not be eaten; a good rule of thumb
is: the higher the GI, the smaller the portion. This, in fact, is exactly
how you control the glycemic load! And this, in fact, is exactly why
low GI foods wind up prevailing: the patient can eat larger quantities
without a glycemic overload!
Distribute the remainder of the calories as you would for a healthy
balanced diet.
To learn more about the glycemic index, look for Good Carbs, Bad Carbs
or a book series called The
Glucose Revolution. Clear, interesting hands-on information awaits
you, your practice and, of course, the patients you want to help. You
can also go to www.biochem.usyd.edu.au/~jennie/GI/glycemic_index.html
where you will find an index and search engine for all foods
To Visit Johanna’s other
articles click here.
Johanna
Burani, MS, RD, CDE has spent the last 15 years in nutrition
counseling, specializing in individually designed meal plans based on
low glycemic index food choices.
Ms. Burani has worked with leading international scientists researching
the glycemic index for the past six years and after contributing to
11 books has recently authored her new book “Good Carbs, Bad Carbs”.
Her book was just selected this year’s #1 diet book by
Self Magazine
