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AN INTRODUCTION TO THE GLYCAEMIC INDEX
Carbohydrates- "Simple" or "Complex"?
Current studies into the physiological responses to the foods that we eat have
provided a much more complex picture than was first thought, particularly with
regard to the way in which the human body responds to carbohydrates in the diet.
Carbohydrates (starches and sugars) are the body's main source of fuel. This
is of course unless you are following a reduced or critically low carbohydrate
(ketogenic) diet, where the body begins to burn ketones (cleaved from fats)
for its primary energy source. Different carbohydrates are known to have different
effects on the body's blood-sugar levels and the pancreas release of the anabolic
hormone insulin, however, predicting exactly the effect of one carbohydrate
compared to another has, in the past, proved difficult. It was generally assumed,
for many years unfortunately, that complex carbohydrates (mainly starches) were
digested and absorbed slowly and therefore raised blood-sugar levels slowly
and steadily, as opposed to simple sugars which rapidly increased blood-sugar
levels. However, studies now suggest that this explanation is too 'simple' as
many starchy foods have been shown to be digested and absorbed rapidly, whilst
some sugary foods do not produce the dramatic rises in blood sugar previously
thought. This is a major point to consider when you are applying science to
your food choices. However, it is not the most critical factor by any means.
More recent studies have shown that, yes blood sugar levels are important, especially
for health reasons, but in terms of the look of your physique and how you feel,
the response of insulin to the foods you digest is far more critical. You can
learn more about this under the section of the insulin index.
The Glycaemic Index was developed in 1981 by Dr. David Jenkins, a Professor
of nutrition at the University of Toronto as a tool to better understand how
the body responds to carbohydrates. It is essentially a ranking of a catalogue
of foods from 0 - 100 that tells us whether a food will raise blood sugar levels
dramatically, moderately, or a little. Dr. Jenkins initially developed the Glycaemic
Index to help determine which foods were most suitable for people with diabetes,
but it can equally be used as a tool by anybody as it is now a scientifically
validated tool in the dietary management of diabetes, weight reduction and athletic
performance. Researchers tested a number of common foods and monitored the blood-sugar
response of a group of subjects. Some of the results were surprising, for example;
ice cream, despite its high simple sugar content had a much more moderate effect
on blood-sugar levels than ordinary bread containing previously termed 'complex'
carbohydrates.
In brief, carbohydrates that break down quickly during digestion have a high
Glycaemic Index (GI) Factors, the blood sugar response is fast and high. Carbohydrates
which break down slowly, effecting blood-sugar levels gradually, have low GI
Factors.
The GI Factor of foods allows you to make a fair comparison between foods as
each food has been compared with a reference food such as pure glucose and tested
in equivalent carbohydrate amounts.
Why is this relevant to you?
The rate of carbohydrate digestion in the gastrointestinal tract has important
implications for everybody. Foods with a low GI Factor help people control their
hunger, their appetite and their bloodsugar levels. Such foods can even prolong
athletic endurance when eaten prior to an event.
Also, as previously mentioned, carbohydrates provide the optimum fuel for the
human body- glucose. Glucose is so vital to the human body that if your diet
doesn't provide enough, your brain signals a deficit and muscle tissue will
be broken down to make up the loss.
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