The glycemic
index: methodology
Thomas
David
MS
Wolever,
ABSTRACT utility
There
ofclassifying
by using
JA Jenkins,
is controversy
foods
the glycemic
index
cent
studies
support
determined
the
of glycemic
the glycemic In long-term
the
glycemic
ofthe
utility
clinical responses
controversy
of the
GI difference
responses,
is due
the
GI.
interRe-
Within
limits
and by the day-to-day
GI
predicts
the
ranking
in overall
blood
non-insulin-dependent
and
therapeutic
glucose
control
importance
secretion
and
with
hypertriglyceridemia.
KEY
WORDS
in patients
with
diabetes.
of
is the ability lower
blood
Diabetes,
of bow-GI
lipid Am
Nutr
The
systematic
classification was
testing
of foods
first
undertaken
The
individual
foods,
glycemic
a classification information It was
individual
glycemic
index
index
(GI)
according
reasoned
that
allowed
knowledge
be ofuse
effects
of whole
diets.
Unexpected
values
of different factors
their
not
foods given
It was proposed utility:
of insulin
food
is expressed
to their diet con-
independently
as
of the
glycemic
in understanding
helped
in food
differences
between
to highlight tables
such
effects
of
the physiologic the
the importance as food
form,
GI
of
large
space
and
that
the GI should
fulfill
four
to mixed
meals,
and
4) demonstration
improvements is to address
by practical these criteria
responses.
However,
it is recognized
profoundly
subject’s
of
criteria
to be
for
high
if any,
GI value
for a test
is
starting curve
response
to
the resulting food.
food
is an outlier,
it could
be due to an unrepresentative or test food or to the subject having
An unrepresentative
is suspected also outliers
variability
agent,
and 5-10 mm before the glycemic-response
of the mean
the mean,
if the in the
the
repeated
value.
If the
a to the
response
subject’s GI values for other same direction, or if there is standard
tests,
response
with
one
very
food seems representative, repeated testing of the test food may be carried out. The outlying result can be discarded if two further tests result in a GI value similar to that for the rest ofthe group but must be suspected as real ifa repeated test produces a similar
to the standard
result. Important
variables
that
food-portion
size, choice
the
food,
standard
method body
frequency
and method of blood
fatness,
affect
the
GI value
of standard and
food,
length
obtained
repeated
of time
ofarea
calculation.
Other
sampling;
subject
characteristics,
glucose
tolerance
status;
include
testing
of blood
factors
of sam-
include
the
eg, age,
sex,
dose and timing
of insulin
of clinically dietary changes in light of data
that have appeared since they were proposed. In addition, the methods for calculating and applying the GI values offoods will be defined. The GI is not the only valid way to analyze blood may influence
hypoglycemic
subject, and value for the
individual
low or very
finger-prick
as a percent
2 SD from
standard food test foods are
particle
antinutrients, properties
>
Capillary
subjects
taken by the same to obtain the GI
response to the standard true idiosyncratic response.
proportional impact ofthe
(6).
for normal
or oral
(1),
1) consistency of values for the same food time, 2) application in individual subjects, 3)
significant therapeutic (3, 4). Our purpose
846
for each
pling,
of clinical
factors
subjects
gly-
foods.
glucose
60, 90, and dose
subject
fasting and at 15, 120 mm after the start of the test meal, and fasting and at 30-mm intervals for 3 h. The
Niklas
incorporation
size, the nature ofthe starch, food processing, and which may have large effects on the physiologic
application
by each
taken
to their and
was developed
might
across
are
ie,
of the glycemic effects of foods to supplement about chemical composition given in food tables
foods
food
times
taken after the fasting blood sample to eat the test meal. The area under
1991;54:846-54.
by Otto
into the diabetic diet in amounts inversely glycemic responses to keep the glycemic
(2).
three samples
normal
Ifan
after
stant.
oftest
the standard food values are averaged
responses
who,
methodology
foods and white bread containing 50 g available carbohydrate are fed to normal or diabetic subjects in random order on separate occasions after an overnight fast. To reduce variability the standard food (white bread) should be repeated
30, 45,
Introduction
cemic
index
for diabetic
to reduce in patients
carbohydrate,
Glycemic
blood
greater
diets
concentrations
J Clin
diet,
perhaps
G Josse
response data (5). Thus, valid conclusions regarding the clinical utility ofclassifying foods according to their glycemic responses can be obtained only with appropriate and consistent methods.
at least
insulin-depen-
Of
and Robert
Portions
potential of different meals in individual subjects. trials, bow-GI diets result in modest improvements
dent insulin
Part
L Jenkins,
can markedly affect the and the GI values obtained.
clinical
by the expected
variation
to their
(GI).
to methodologic variables that pretation ofglycemic responses
Alexandra
regarding
according
and clinical implications”2
that
the interpretation
methodologic
of glycemic-
Am J C/in Nuir
I From the Department ofNutritional Sciences, Faculty of Medicine, and the Clinical Nutrition and Risk Factor Modification Centre, St Michad’s Hospital, University of Toronto. 2 Address reprint requests to TMS Wolever, Department of Nutritional Sciences, University ofloronto, Ontario, Canada M5S lA8. Received November 26, 1990. Accepted for publication April 17, 1991.
199 1;54:846-54.
Downloaded from https://academic.oup.com/ajcn/article-abstract/54/5/846/4694343 by guest on 28 February 2018
Printed
in USA.
© 199 1 American
Society
for Clinical
Nutrition
GLYCEMIC or oral
hypoglycemic
particularly
in
agent;
subjects,
the fasting
Although
subject
may
have
major
effects
if they
sponse
to all foods
glycemic
blood
ofdiabetes
diabetes
glucose
value treatment, on the absolute
are standardized
they
similarly
GI value,
and
usually
control, mellitus
and,
(IDDM)
on the day of the test. and degree of control glycemic response ob-
characteristics,
tamed,
the resulting
the degree
insulin-dependent
appear
so have
to influence only
by influencing
small
the
re-
effects
on
the variability
of
responses.
Food-portion
INDEX
that other standard foods could be used but to allow comparison with GI5 or GI,,, values, the standard chosen should be compared carefully with white bread or glucose before doing other tests.
Number
the
size has a major
Food-portion glycemic
responses
are
related
effect to the
on the GI value carbohydrate
because
load
(2, 7).
The dose response for an intermediate GI food, bread, and for glucose appears to be nearly linear up to 50 g available carbohydrate, but the dose response flattens between 50 and 100 g. The GI is based on 50 g available-carbohydrate portions (2). Thus, food-portion sizes based on food tables or food analyses that do not give accurate dietary fiber values may result in portion sizes that contain 50 g available carbohydrate, leading to an
index: methodology
Thomas
David
MS
Wolever,
ABSTRACT utility
There
ofclassifying
by using
JA Jenkins,
is controversy
foods
the glycemic
index
cent
studies
support
determined
the
of glycemic
the glycemic In long-term
the
glycemic
ofthe
utility
clinical responses
controversy
of the
GI difference
responses,
is due
the
GI.
interRe-
Within
limits
and by the day-to-day
GI
predicts
the
ranking
in overall
blood
non-insulin-dependent
and
therapeutic
glucose
control
importance
secretion
and
with
hypertriglyceridemia.
KEY
WORDS
in patients
with
diabetes.
of
is the ability lower
blood
Diabetes,
of bow-GI
lipid Am
Nutr
The
systematic
classification was
testing
of foods
first
undertaken
The
individual
foods,
glycemic
a classification information It was
individual
glycemic
index
index
(GI)
according
reasoned
that
allowed
knowledge
be ofuse
effects
of whole
diets.
Unexpected
values
of different factors
their
not
foods given
It was proposed utility:
of insulin
food
is expressed
to their diet con-
independently
as
of the
glycemic
in understanding
helped
in food
differences
between
to highlight tables
such
effects
of
the physiologic the
the importance as food
form,
GI
of
large
space
and
that
the GI should
fulfill
four
to mixed
meals,
and
4) demonstration
improvements is to address
by practical these criteria
responses.
However,
it is recognized
profoundly
subject’s
of
criteria
to be
for
high
if any,
GI value
for a test
is
starting curve
response
to
the resulting food.
food
is an outlier,
it could
be due to an unrepresentative or test food or to the subject having
An unrepresentative
is suspected also outliers
variability
agent,
and 5-10 mm before the glycemic-response
of the mean
the mean,
if the in the
the
repeated
value.
If the
a to the
response
subject’s GI values for other same direction, or if there is standard
tests,
response
with
one
very
food seems representative, repeated testing of the test food may be carried out. The outlying result can be discarded if two further tests result in a GI value similar to that for the rest ofthe group but must be suspected as real ifa repeated test produces a similar
to the standard
result. Important
variables
that
food-portion
size, choice
the
food,
standard
method body
frequency
and method of blood
fatness,
affect
the
GI value
of standard and
food,
length
obtained
repeated
of time
ofarea
calculation.
Other
sampling;
subject
characteristics,
glucose
tolerance
status;
include
testing
of blood
factors
of sam-
include
the
eg, age,
sex,
dose and timing
of insulin
of clinically dietary changes in light of data
that have appeared since they were proposed. In addition, the methods for calculating and applying the GI values offoods will be defined. The GI is not the only valid way to analyze blood may influence
hypoglycemic
subject, and value for the
individual
low or very
finger-prick
as a percent
2 SD from
standard food test foods are
particle
antinutrients, properties
>
Capillary
subjects
taken by the same to obtain the GI
response to the standard true idiosyncratic response.
proportional impact ofthe
(6).
for normal
or oral
(1),
1) consistency of values for the same food time, 2) application in individual subjects, 3)
significant therapeutic (3, 4). Our purpose
846
for each
pling,
of clinical
factors
subjects
gly-
foods.
glucose
60, 90, and dose
subject
fasting and at 15, 120 mm after the start of the test meal, and fasting and at 30-mm intervals for 3 h. The
Niklas
incorporation
size, the nature ofthe starch, food processing, and which may have large effects on the physiologic
application
by each
taken
to their and
was developed
might
across
are
ie,
of the glycemic effects of foods to supplement about chemical composition given in food tables
foods
food
times
taken after the fasting blood sample to eat the test meal. The area under
1991;54:846-54.
by Otto
into the diabetic diet in amounts inversely glycemic responses to keep the glycemic
(2).
three samples
normal
Ifan
after
stant.
oftest
the standard food values are averaged
responses
who,
methodology
foods and white bread containing 50 g available carbohydrate are fed to normal or diabetic subjects in random order on separate occasions after an overnight fast. To reduce variability the standard food (white bread) should be repeated
30, 45,
Introduction
cemic
index
for diabetic
to reduce in patients
carbohydrate,
Glycemic
blood
greater
diets
concentrations
J Clin
diet,
perhaps
G Josse
response data (5). Thus, valid conclusions regarding the clinical utility ofclassifying foods according to their glycemic responses can be obtained only with appropriate and consistent methods.
at least
insulin-depen-
Of
and Robert
Portions
potential of different meals in individual subjects. trials, bow-GI diets result in modest improvements
dent insulin
Part
L Jenkins,
can markedly affect the and the GI values obtained.
clinical
by the expected
variation
to their
(GI).
to methodologic variables that pretation ofglycemic responses
Alexandra
regarding
according
and clinical implications”2
that
the interpretation
methodologic
of glycemic-
Am J C/in Nuir
I From the Department ofNutritional Sciences, Faculty of Medicine, and the Clinical Nutrition and Risk Factor Modification Centre, St Michad’s Hospital, University of Toronto. 2 Address reprint requests to TMS Wolever, Department of Nutritional Sciences, University ofloronto, Ontario, Canada M5S lA8. Received November 26, 1990. Accepted for publication April 17, 1991.
199 1;54:846-54.
Downloaded from https://academic.oup.com/ajcn/article-abstract/54/5/846/4694343 by guest on 28 February 2018
Printed
in USA.
© 199 1 American
Society
for Clinical
Nutrition
GLYCEMIC or oral
hypoglycemic
particularly
in
agent;
subjects,
the fasting
Although
subject
may
have
major
effects
if they
sponse
to all foods
glycemic
blood
ofdiabetes
diabetes
glucose
value treatment, on the absolute
are standardized
they
similarly
GI value,
and
usually
control, mellitus
and,
(IDDM)
on the day of the test. and degree of control glycemic response ob-
characteristics,
tamed,
the resulting
the degree
insulin-dependent
appear
so have
to influence only
by influencing
small
the
re-
effects
on
the variability
of
responses.
Food-portion
INDEX
that other standard foods could be used but to allow comparison with GI5 or GI,,, values, the standard chosen should be compared carefully with white bread or glucose before doing other tests.
Number
the
size has a major
Food-portion glycemic
responses
are
related
effect to the
on the GI value carbohydrate
because
load
(2, 7).
The dose response for an intermediate GI food, bread, and for glucose appears to be nearly linear up to 50 g available carbohydrate, but the dose response flattens between 50 and 100 g. The GI is based on 50 g available-carbohydrate portions (2). Thus, food-portion sizes based on food tables or food analyses that do not give accurate dietary fiber values may result in portion sizes that contain 50 g available carbohydrate, leading to an
