High carbohydrate foods are the basis of diets around the
world. Both the quantity and quality of carbohydrate intake are important in
optimal nutrition. In Asia, where rice is a staple food, carbohydrates provide
as much as 80% of the fuel in the diet. Carbohydrate makes up more than 50% of
the energy in a typical American’s diet. Carbohydrate provides energy for the
brain, central nervous system and muscle cells. The sugar glucose is the most
important carbohydrate. It is as glucose that dietary carbohydrate is absorbed
into blood stream. Normal blood glucose levels are about 80 to 120 mg per 100
ml of blood. This level is regulated primarily by the hormones Insulin and
glucagon. Controlling carbohydrate
intake plays a central role in maintaining normal glucose level
(normoglycemia). Eating too much carbohydrate at one time can raise blood
glucose too high stressing the insulin – producing cells. Eating too little
carbohydrate can lead to abnormally low blood sugar (hypoglycemia). The diets
high in carbohydrates have been blamed for everything from obesity to diabetes.
The reason for this is related to the types and sources of dietary
carbohydrates.
The glycemic response
A rise in blood glucose levels can be detected shortly after
eating carbohydrate – rich foods. The impact of different foods on the
magnitude and duration of the rise in blood glucose after a meal is called glycemic
response. A rating system known as the glycemic index (GI) is developed to
classify foods according to their relative glycemic response.
The glycemic index (GI)
The glycemic index (also glycaemic index, GI) is a measure
of the extent of the change in blood glucose content (glycemic response)
following consumption of digestible carbohydrate, relative to a standard such
as glucose. The glycemic index was developed by David Jenkins, Thomas Wolever
and colleagues at the University of Toronto in 1981. GI ranks the quality of
individual carbohydrate – rich foods on a scale of 1-100 by measuring how
glucose levels rise in blood after someone eats an amount of that food
containing 50grams of carbohydrate.
The GI measurement
The glycemic index is a numerical index that ranks
carbohydrates based on their rate of glycemic response. In the first step about
50 grams of available carbohydrates have been consumed and the blood sugar
levels are measured over a period of 2 hours. The changes in blood glucose over
time are plotted as a curve (glucose response curve). In the second step about 50
grams of two control foods, either white bread or pure glucose have been
consumed. Once again blood sugar levels are measured over a period of two
hours. Another curve is plotted and the glucose AUCs or “area under the curves”
are compared. The glycemic index is
calculated as the area under the glucose curve after the test food is eaten,
divided by the corresponding area after the control food is eaten. The value is
multiplied by 100 to represent a percentage of the control food. For example,
if a person consumes a starchy vegetable like green peas and the glucose AUC is
48%. In this case the GI for green peas would be calculated at 48% of 100 or simply
48. Glycemic index uses a scale of 1 to 100 with high values given to foods
that cause the most rapid rise in blood sugar. The glycaemic index is
influenced by the amount of carbohydrate, nature of the sugar components, and
nature of starch, cooking / food processing and other food components such as
fats, proteins, dietary fibres, anti-nutrients and organic acids.
Definition of Glycemic index
For a given food, glycemic index is defined as the
incremental area under the glucose response curve 2 hours after consumption of
50 grams of carbohydrate from a test food relative to the same amount of available
carbohydrate from a control food (either white bread or pure glucose). It
reflects the rate at which the carbohydrate in the food is digested and
absorbed into the blood stream.
The Glycemic index ranking system
The glycemic index is a ratio of the blood glucose response
to a given food compared to a standard (pure glucose or white bread).Glycemic
index uses pure glucose as its control food and rates all other carbohydrates
in relation to it. It measures the rate and degree of blood sugar elevation
following the consumption of a single food carbohydrate. It provides a
numerical, evidence -based index of postprandial (post-meal) glycemic response.
The glycemic index’s ranking system is only for carbohydrates and not for fats
or proteins.
Carbohydrates are broadly categorized by the glycemic index
as high (70 or greater), medium(56 to 69) and low glycemic (0 to 55) rating system. High
glycemic carbohydrates enter the blood stream quickly and readily available for
the body. Low glycemic carbohydrates enter the blood stream slowly and help maintain
stable blood sugar levels in an extended period of time. Lower glycemic
eating improves overall health, maintain
lean body mass and reduces the risk of cardiovascular disease, type 2 diabetes,
metabolic syndrome, stroke, depression, chronic kidney disease, formation of
gall stones and cancers of the breast, colon, prostate and pancreas. The glycemic index helps as a useful guide
for persons with diabetes to help keep their blood sugar levels in the healthy
range. The GI index is also used for weight loss and weight management.
GI classification of food carbohydrates
High GI foods such as white breads, white rice, cornflakes,
baked potatoes, chips, rice crackers, muffins doughnuts and popcorn score
between 70 and 100. Medium GI foods scoring between 55 and 70 include
whole-grain cereals, brown rice, quick oats, some cakes and cookies, table
sugar and energy bars. Low GI foods
scoring between 0 and 55 include all vegetables, most fruits, oatmeal, barley, nuts
and seeds and most whole-grain products. Eating food with a glycemic index of
75 or above causes irritability, mood swings and excess weight gain. Eating
foods with a glycemic index below 60 tends to conserve insulin, energy and
moods, balances hormones and adds to our anabolic capacity. We should select our daily foods with a
glycemic index of 60 and below.
The Glycemic load, GL
Walter Willett and colleagues at the Harvard School of
Public Health created the concept of glycemic load (GL). Glycemic load combines
both quality and quantity of a carbohydrate in one number. It is an excellent
way to predict blood glucose values of different types and amounts of food.
The glycemic load of a food is calculated
by multiplying the glycemic index by the amount of carbohydrate in grams
provided by a food and dividing the total by 100. Dietary glycemic load is the
sum of the glycemic loads for all foods consumed in the diet. The average range
in the glycemic load is lower than the glycemic index.
High Glycemic load = 20 or more; Medium
Glycemic Load = 11 – 19; Low Glycemic load = 10 or less.
A glycemic load of 0-10 is considered low
(slow, steady conversion to blood sugar), whereas a high glycemic load is 20
and more (sudden spike in blood glucose, tough on health and body homeostasis).
How to follow glycemic index diet
The glycemic index of foods is of primary
importance for keeping blood glucose under control. Our management of blood
glucose over time appears to depend on our regular food choice and life style.
Try to start the day with a great breakfast of low glycemic index foods. Eat a
balanced diet with a variety of nutrient – dense foods every day. Try to choose
whole – grain foods over processed foods. Try to have at least one food from the lower
glycemic index list at every meal. Do choose foods that are high in fibre to
prolong your digestion time. Do choose a diet rich in fresh vegetables, fruits
and beans. Don’t mix too many foods together. Don’t over-eat or take too large
portions. Over eating encourages insulin resistance, which leads to weight
gain. Choose foods with little added sugar or calorific sweeteners. Be cautious
of the types of fats that you choose. Use in moderation of unhealthy items such
as salt, caffeine or alcohol. Try your best to make small changes in your
dietary habits. Remember even the small changes are still changes.
Benefits of GI awareness
Glycemic index helps anyone making the
best choices of low glycemic foods.Knowing the glycemic index foods, one can
virtually eliminate the risk of contracting diabetes. Eating low glycemic
foods protects our insulin response from becoming overtaxed, which in turn keeps
our heart, brain and other organs healthier. Over consumption of high glycemic index
foods encourages the risk of heart disease and strokes. Focusing on food from
low glycemic index list will significantly improve one’s heart health. By
following the glycemic index, one can choose low glycemic foods which helps to
lose weight and reduce the risk of developing diabetes, will also help to lower
one’s level of blood cholesterol, which in turn will eliminate the risk of
several chronic diseases. The low glycemic index eating is life – style friendly
and keeps our sugar and insulin levels on a healthy and constant plateau.
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