Using the glycemic index to compare carbohydrates

Carbohydrates are often divided
into two categories — simple and
complex. Simple carbohydrates
include mono- and disaccharides
(i.e. fruit sugars and table sugars)
and tend to be absorbed faster
than complex carbohydrates or
polysaccharides (i.e. breads,
pasta, grains). However, due to
the varying rates of digestion and
absorption between different
carbohydrates, such simple
classifications may not always be
the most useful.

What is the glycemic index?
Foods are assigned glycemic
index numbers based on the
comparative increases in blood
glucose (sugar) levels they
produce when eaten.

A low- to
moderate-glycemic food causes a
slow, gradual rise in blood sugar,
and maintains the increased
energy level for a longer duration.

A high-glycemic food increases
the blood sugar concentrations
quickly, thus providing energy to
the body in a short period of
time. However, insulin is released
in response to this rise in blood
sugar, which, in turn, brings the
blood sugar down fairly rapidly.
This rapid decrease reduces the
energy supply and may trigger
hunger.

How is the glycemic index
determined?

Specific procedures can vary with
the researcher. In general, human
subjects are fed 50 grams of
carbohydrate from a specific food.
The subjects’ blood glucose levels
are measured at intervals over the
following two hours to monitor the
blood glucose response.

By comparing the area under the
graphed line with that obtained
from consuming 50 grams of pure
glucose, a percentage is
determined. For example, a
glycemic index of 60 indicates that
consuming 50 grams of that food
causes an increase in blood
glucose 60 percent as great as that
produced by eating 50 grams of
pure glucose.

Glossary
Amylopectin — a component of
starch that has a high
molecular weight and
branched structure and does
not tend to gel in aqueous
solutions

Amylose — a component of
starch characterized by its
straight chains of glucose units
and by the tendency of its
aqueous solutions to set to a
stiff gel

Disaccharide — two chain
molecules of sugars

Epidemiological studies —
medical science that deals with
the incidence, distribution,
and control of disease in a
population

Glycogen — the principal form in
which carbohydrates are stored
in the body

Glucose — sugar

Glycemic index — measurement
based on the amount of
increase in blood glucose levels
after eating a specific food

Lipid — another term for fat

Monosaccharide — single chain
molecules of sugars

Polysaccharide — multiple chain
molecules of sugars


What factors influence the
glycemic index of foods?

Many factors can influence the
glycemic index. Often foods with
different glycemic indexes are
consumed simultaneously, which
affects the glycemic index of the
individual foods. In addition,
other factors that can influence the
glycemic index include:

  • Biochemical structure of the
    carbohydrate — for example,
    amylopectin is more readily
    absorbed than amylose
  • Intestinal absorption
  • Food particle size — smaller
    particles are absorbed faster
  • Mechanical and thermal
    processing — both break the
    food into smaller particles thus
    facilitating absorption
  • Content and timing of the
    previous meal
  • Accompanying foods that
    include fat, fiber, or protein —
    fat and protein decrease the
    speed with which the stomach
    empties, thus decreasing the
    rate of carbohydrate absorption,
    which reduces the rate of
    elevating blood glucose and
    produces a lower glycemic
    index.

    Why is the glycemic index
    important?

    People need the energy provided
    by food; they react to a lack of
    food by feeling hungry. Monitoring
    energy levels is especially
    important for athletes and people
    with health implications, such as
    diabetes mellitus.

    Due to the
    importance of balancing blood
    glucose levels in diabetics, low to
    moderate glycemic foods are
    recommended to moderate blood
    glucose in these individuals.

    Athletes often choose foods that
    optimize their glycogen stores.
    Most athletes benefit the most
    from eating foods having a low to
    moderate glycemic index in their
    pre-game meal, and then eating
    high-glycemic foods immediately
    after exercise.

    However, the post-activity
    meal also should contain
    low to moderate glycemic foods
    for optimal glycogen storage.

    Proponents and critics debate both
    the merits of the glycemic index
    and how it is calculated.

    Clinical trials researching
    meals with different glycemic
    indexes confirm that eating
    low-glycemic foods helps
    blood glucose levels stay more
    level and thus reduces the
    amount of insulin released
    after a meal.

    When blood
    glucose levels are fairly even
    between meals, fat is also
    metabolized at a healthier rate
    so blood lipid levels remain
    comparatively even.

    Monitoring the glycemic index
    for various foods is one way
    diabetics can try to control
    their blood glucose levels.
    Studies where dietary habits
    have been examined indicate
    that foods with higher-glycemic indexes are a risk
    factor for diabetes, obesity, and
    cardiovascular disease.

    Groups
    consuming high-glycemic
    foods were at greater risk of
    developing chronic disease
    than did the groups
    consuming foods with lower
    glycemic indexes.

    Critics have raised several
    concerns regarding how the
    glycemic index is calculated.

  • Differences in glycemic
    indexes are falsely elevated
    when based only on a
    comparison of the
    differences in blood glucose
    elevation instead of on the
    entire change in blood
    glucose levels.

  • The time used in many
    studies (2 hours) is too
    short. Monitoring blood
    glucose levels over a four-hour
    period would show fewer
    differences between foods.

  • The type of dietary
    investigations on which the
    epidemiological studies base
    their arguments are not
    detailed enough to catch the
    many variations in the
    glycemic indexes.

    The
    glycemic index can vary
    with varieties within a food
    group, method of
    preparation, growing
    conditions, geographic
    locations, genetic strain,
    ripeness, acidity, fiber,
    protein, and fat content of
    foods.

  • Many epidemiological
    studies show no effect of
    glycemic indexes.
    The glycemic index does not
    necessarily predict the insulin
    response, since it also is
    affected by other factors in
    food, such as the kind of
    protein and the protein
    content.

    Current research is
    investigating whether rapid
    fluctuations in blood glucose
    levels increase the risk of fat
    gain and type 2 diabetes.

    For additional glycemic
    indexes visit these Web
    sites:

    www.diabetesdigest.com/dd_nutrition2.htm

    www.diabetesnet.com/diabetes_food_diet/
    glycemic_index.php

    www.mesquitemagic.com/glycemic_Index_chart.htm.

    Breads & Grains
    waffle – 76

    doughnut – 76

    bread, whole wheat – 73

    bagel – 72

    wheat bread, white – 70

    cornmeal – 68

    bran muffin – 60

    rice, white – 56

    rice, brown – 55

    wheat kernels – 48

    rice, instant (1 minute) – 46

    bulgur – 46

    spaghetti, white – 41

    spaghetti, whole wheat – 32

    barley – 25

    Cereals
    Rice Krispies® – 82

    Grape Nuts Flakes® – 80

    Corn flakes – 77

    Cheerios® – 74

    Shredded wheat – 67

    Grape Nuts® – 67

    Life® – 66

    All Bran® – 38

    Fruits
    watermelon – 72

    pineapple – 66

    raisins – 64

    banana – 51

    orange – 48

    grapes – 43

    apple – 40

    pear – 33

    Starchy vegetables
    carrots – 92

    potatoes, instant – 88

    potatoes, baked – 78

    potatoes, mashed – 73

    sweet potatoes – 48

    Legumes
    baked beans – 40

    butter beans – 36

    split peas – 32

    lentils – 28

    kidney beans – 23

    soy beans – 15

    Dairy
    ice cream – 62

    yogurt, low fat sweetened – 33

    milk, skim – 32

    milk, full fat – 21

    Snacks
    rice cakes – 82

    jelly beans – 80

    graham crackers – 74

    Life Savers – 70

    angel food cake – 67

    wheat crackers – 67

    potato chips – 57

    popcorn – 55

    oatmeal cookies – 54

    banana cake – 47

    chocolate – 44

    corn chips – 42

    peanuts – 13

    Sugars
    honey – 87

    sucrose – 60

    lactose – 43

    fructose – 20

    Beverages
    soft drinks – 63

    orange juice – 57

    apple juice – 41

    Glycemic Indexes of Common Foods
    Foods are listed from highest to lowest glycemic index within
    the category. Glycemic index was calculated using glucose as the
    reference with glycemic index of 100. (The University of Sidney,
    www.glycemicindex.com). No endorsement of companies or
    their products is intended nor is
    criticism implied of similar
    companies or their products that are
    not included.

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