GI measures effects of carbohydrates
with respect to their ability to raise
blood glucose and compares this value
with blood glucose response to either
white bread or glucose itself. Glycemic
load (GL), introduced in 1997, mea-
sures the blood glucose response to a
specific weight of a given food. GL,
therefore, provides a measure of total
glycemic response to a food or meal. It
is calculated by multiplying the amount
of carbohydrate contained in a serving
size (weight in grams or volume in mil-
liliters) by the GI value of that food
divided by 100.
Simply stated, the glycemic response
to a food is a measure of the impact of a
food on blood sugar. Foods with rapidly
hydrolyzed and absorbed carbohydrates
generally have a fast and high impact on
blood sugar, resulting in the highest
glycemic indexes. Slowly or incom-
pletely digested carbohydrates have low
glycemic indexes. In these cases, glu-
cose is released gradually into the
blood, and the blood sugar response is
slow and steady.
In recent years, numerous products
bearing terms such as "net carbs,"
"impact carbs," "low GI," etc., on
packaging have appeared on grocery
shelves. This information appears out-
side the Nutrition Facts Panel, as these
terms are not approved by FDA. Food
manufacturers also place on the product
package a statement indicating that only
the "net carbs" or "impact carbs" affect
blood glucose. Such products have
increased consumer awareness of
glycemic response.
Clinical significance of GI
Health problems related to being
overweight are becoming the major
health concern of the industrialized
world. The World Health Organization
and Food and Agriculture Organization
of the United Nations (WHO/FAO)
have stated that, globally, overweight is
a bigger problem than undernourish-
ment. In "Carbohydrates in Human
Nutrition," they recommended that peo-
ple in industrialized countries base their
diets on low-GI foods to prevent most
common diseases of affluence.
High-glycemic foods may stimulate
a high insulin demand that, in turn, can
lead to postprandial hypoglycemia,
which may be implicated in triggering
hunger. Lower-glycemic foods usually
provoke less insulin demand and less
possibility of hypoglycemia. Hence,
lower-glycemic foods may help con-
sumers to eat fewer calories. It is impor-
tant to note, however, that the relation-
ship between GI and insulin demand is
not always linear, and various compo-
nents of the food can modify insulin
response relative to glycemic response.
Also, the glycemic response of individ-
ual foods and ingredients is influenced
by the presence of other foods, process-
ing conditions, etc.
The clinical significance of GI
remains the subject of intense debate.
However, it is clear that the rate and the
amount of carbohydrate absorption after
a meal have significant effects on post-
prandial hormonal and metabolic
responses. The habitual consumption of
high-GI foods may increase risk factors
associated with obesity, type 2 diabetes
and heart disease. Conversely, the con-
sumption of foods that elicit low-
glycemic responses may help to reduce
such risk factors. GL, as defined above,
may be a better predictor of likely
health outcomes than GI, per se.
In July 2002, the American Journal
of Clinical Nutrition published a special
supplement that reviewed the history of
GI, the current status of knowledge and
recommendations for future studies.
Calculating the precise glycemic response
of a given food can prove difficult, partic-
ularly with unprocessed agricultural ingre-
dients like fresh fruit, which can have
varying GIs, depending on the degree of
ripeness and other variables.
