It's
mid-afternoon and those dreaded munchies strike again! Reaching
for the nearest candy bar, you wonder just how long you can keep
those hunger pangs at bay. Everyone knows that sugars are rapidly
absorbed and cause your blood sugar levels to rise and then dive
just as quickly, meaning that you will be starving again in an
hour. Right? Wrong. That old story has been turned upside down as
researchers find out more about the physiological effects of foods
on blood sugar levels and hence hunger. AFIC recently caught up
with Associate Professor Jennie Brand-Miller at the lLSI/FAO
meeting on Food-Based Dietary Guidelines in Kuala Lumpur,
Malaysia. Part of the teaching and research staff of the Human
Nutrition Unit at the University of Sydney, Australia, she has
been undertaking research into carbohydrates for the last twenty
years. We discussed the "glycaemic index", a measure of how foods
affect blood sugar levels, and its implications for Asian diets.
AFIC: What is the glycaemic index
of a food?
Brand-Miller: The glycaemic index
(G.I.) is a way of measuring the effects of food on blood sugar
levels. It is a ranking from 0 to 100 which rates the increase in
blood sugar levels after eating a portion of food providing 50
grams of carbohydrate. A 50-gram portion of pure glucose is used
as the basis of comparison. Foods that break down quickly during
digestion, for example rice, have the highest glycaemic indices.
They raise blood sugar levels higher and more quickly than foods
with low G.I.s. Low G.I. foods, such as baked beans, break down
more slowly, releasing sugar gradually into the bloodstream.
AFIC: Were there any surprises in
the research findings on the G.I. factors of foods?
Brand-Miller: There were many!
Originally it was believed that "complex" carbohydrate foods, such
as bread, rice and potatoes, were digested slowly, causing a
gradual increase in blood sugar levels. However, we found that
many starchy foods are digested very rapidly and absorbed quickly.
They are high G.I. foods. On the other hand, moderate amounts of
most sugary foods, such as confectionery and ice cream, did not
produce dramatic increases in blood sugar as had always been
thought. The truth is that foods containing sugar actually showed
quite low-to-moderate blood sugar responses - lower than foods
like rice.
AFIC: What are the implications of
these findings?
Brand-Miller: Traditionally,
scientists have always explained carbohydrates in terms of
chemical structure, referring to "complex" and "simple"
carbohydrates. However, studies have shown us that this concept is
inconsistent with how carbohydrates are actually broken down and
absorbed by the body. It's time to forget the old distinctions
between "starchy" and "sugary" foods or "simple" versus "complex"
carbohydrates, Instead, we need to look at how rapidly a
carbohydrate-containing food is absorbed and how it affects blood
sugar levels.
AFIC: What is the relevance of the
G.I. concept to healthy eating?
Brand-Miller: Now that we can
distinguish between low and high G.I. foods, we can encourage
people to increase their intake of low G.I. foods so they have a
slower digestion and absorption of sugar into their bloodstream.
If we encourage people to eat low G.I. foods, they should have a
lower fat diet that keeps them feeling full for longer periods.
This means they tend to eat less and take in fewer calories. A
diet that concentrates on low G.I. foods may also help reduce the
risk of other diseases, such as obesity and heart disease.
AFIC: Do you think the G.I.
concept is relevant to Asian diets?
Brand-Miller: The G.I. is even
more relevant to the Asian population. It is interesting to note
that only Caucasians have inherited the insulin-sensitive state,
which means they can cope well with high G.I. foods. Research has
shown that many Asian populations have more insulin resistance,
even when they are young, healthy and lean. It appears that Asians
need a higher insulin response to high G.I. foods and they need to
secrete more insulin to bring their blood sugar levels back to
normal. This puts more of a strain on their pancreas. Considering
the high rates of diabetes in Asians, the use of low G.I. foods
could mean less strain on their pancreas, which in turn may help
delay the onset of diabetes.
AFIC: Rice is a dietary staple in
most parts of Asia. Has the G.I. of rice been studied?
Brand-Miller: Different rice
strains have markedly different G.I.s. A rice strain with a high
amylose (a type of starch) content, for example Basmati rice, has
a low G.I. If rice is sticky and the grains clump together, it is
likely to have a high G.I. factor because there is less amylose
present. Rice that is drier with separate grains generally has a
lower G.I. factor. If people are eating a low fat diet and are
physically active, the G.I. content of their diet is not such a
critical factor. However, the G.I. of the Asian diet is becoming
more important as changes in dietary habits and declines in
physical activity levels occur. Insulin resistance worsens as
people age and put on weight.
AFIC: How does the G.I. relate to
other nutritional aspects of foods?
Brand-Miller: The G.I. has
sometimes been criticised because foods were rated as "good" or
"bad" on the basis of their G.I. factor alone. However, just like
any other nutritional factor, it was never intended that the G.I.
be used in isolation. The total amount of carbohydrate, the amount
and type of fat, the fibre and the salt content of a food are also
important considerations in one's diet.
