add to fAvorites

May 2009
M	T	W	T	F	S	S
« Apr		Sep »
	1	2	3
4	5	6	7	8	9	10
11	12	13	14	15	16	17
18	19	20	21	22	23	24
25	26	27	28	29	30	31

Pharmacy Links

THE G.I. FACTOR: WHAT GIVES ONE FOOD A HIGH G.I. FACTOR AND ANOTHER FOOD A LOW ONE?

08/05/09

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.

The degree of starch gelatinization. The starch in raw food is stored in hard compact granules that make it difficult to digest. This is why potatoes might give you a pain in the stomach if you eat them raw.

Most starchy foods need to be cooked for this reason. During cooking, water and heat expand the starch granules to different degrees, some granules actually bursting and freeing the individual starch molecules. This is what happens when you make a gravy by heating flour and water until the starch granules burst and the gravy thickens.

If most of the starch granules present have swollen and burst during cooking, the starch is said to be fully gelatinised.

The swollen granules and free starch molecules are very easy to digest because the starch-digesting enzymes in the small intestine have a greater surface area to attack. The quick action of the enzymes results in a rapid and high blood sugar rise after consumption of the food (remember that starch is a string of glucose molecules). A food containing starch which is fully gelatinised will therefore have a very high G.I. factor.

In foods such as biscuits, the presence of sugar and fat and very little water, makes starch gelatinisation more difficult, and only about half of the granules will be fully gelatinised. For this reason, biscuits tend to have intermediate G.I. factors.