Biology Reference
In-Depth Information
available carbohydrates. All the foods have to be compared based on the sim-
ilar available carbohydrate levels, which is mostly 50 g using most foods and
in some cases may be reduced to 25 g if the portion size of the food to be
tested is too large with 50 g available carbohydrates. For this reason, this
measure is dependent on the quality of carbohydrates rather than the quan-
tity of the carbohydrates and does not always reflect the typical amount of
carbohydrate that is normally present in a portion of a particular food item
(
Sheard et al., 2004
).
GI is calculated by measuring the postprandial glucose levels over 2 or 3 h
after consumption of the test foods and comparing it with the blood glucose
response following a reference food, such as glucose or white bread with
equivalent amount of available carbohydrates (
Jenkins et al., 1981
)
. This value
is then represented as a percentage to give the GI of the food. The blood glu-
cose response is usually represented as the area under the blood glucose curve,
which often shows a positive relation with the glycemic quality of the food.
High-GI foods are characterized by greater glucose area under the curve and
low-GI foods have lesser glucose area under the curve (
Foster-Powell, Holt, &
Brand-Miller, 2002
)
. In order to consider both the quality and quantity of the
foods in a typical serving of a food, another measure called GL was developed
that allowed the determination of the glycemic response to a portion of the
food (
Beulens et al., 2007
)
. GL is calculated as the product of the GI of a food
and the available carbohydrate in a serving size of that food. This helps the
general public to control the portion sizes of foods based on their GI values
in order to achieve a lowGL value. Irrespective of the availability of these two
measures, GI and GL, at times it is sensible to compare different foods just
based on their glycemic response postprandial because of their effects on other
physiological characteristics such as insulin response and lipid profile (
Schenk,
3. BLOOD GLUCOSE AND CHRONIC DISEASES
The effect of GI on health outcomes in intervention studies has
reported improvements in insulin sensitivity,
b
-cell function, dyslipidemia,
and thrombolytic function. However, there were mixed results due to stud-
ies varying in duration, sample size, subject type, and intervention diet that
did not match for energy, macronutrient, or fiber content. The risk of devel-
oping type 2 diabetes has been found to be increased by 37% in men and
women whose diet came under the highest quintiles of energy-adjusted
GI compared with the lowest quintiles (
Salmeron, Ascherio, et al., 1997;
Salmeron, Manson, et al., 1997
)
. However,
in a 6-year follow-up of
