THE G.I. FACTOR: WHAT GIVES ONE FOOD A HIGH G.I. FACTOR AND ANOTHER FOOD A LOW ONE?
Scientists have been studying what makes one food high and another low for more than fifteen years. There is a wealth of information that can easily confuse. We have summarised the results of their research in the following table which looks at the factors which influence the G.I. factor of a food.
The key message is that the physical state of the starch in the food is by far the most important factor influencing the G.I. value. That’s why the advances in food processing over the past two hundred years have had such a profound effect on the overall G.I. factor of the food we eat.
Amylose and amylopectin. There are two sorts of starch in food— amylose and amylopectin—and researchers have discovered that the ratio of one to the other has a powerful effect on the G.I. factor of a food.
Amylose is a straight chain molecule, like a string of beads. These tend to line up in rows and form tight compact clumps that are harder to gelatinise and therefore digest.
On the other hand, amylopectin is a string of glucose molecules with lots of branching points, such as you see in some types of seaweed. Amylopectin molecules are therefore larger and more open and the starch is easier to gelatinise and digest.
Thus foods that have little amylose and plenty of amylopectin in their starch have higher G.I. factors e.g. Calrose rice and wheat flour. Foods with a higher ratio of amylose to amylopectin have lower G.I. factors including Basmati rice and all sorts of legumes.
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