The glycemic index (GI) is a numerical system of measuring how rapidly ingested carbohydrate raises blood sugar.

Carbohydrates have been ranked from 0 - 100, with low GI foods having a rating of less than 55, medium GI foods a GI of 56 to 69 and foods with a GI of 70 or over being classified as high GI.

Our bodies perform best when blood sugar is kept relatively constant so eating foods with a moderate to low GI is generally desirable for good health.

However, GI is not the only factor to take into account when the goal is to maintain a constant level of blood sugar.  The composition of the actual food being eaten and what it is being eaten with will also affect blood sugar levels.  This is where Glycemic Load comes in.

Glycemic Load is a relatively new way to assess the impact of carbohydrate consumption on blood sugar and it takes into account how much of the carbohydrate needs to be eaten to affect blood sugar.  With a carbohydrate food which contains a lot of fibre or water, more of it could be eaten before affecting blood sugar, even though it may in itself have a high GI.  For example, watermelon has a high GI, but it is high in water, has some fibre and doesn’t actually contain a lot of carbohydrate, meaning the impact on blood sugar isn’t as much as some other GI foods ranked high.

The Glycemic Load of a meal is probably a better way of looking at impact on blood sugar, because when you mix a high GI carbohydrate (i.e. jasmine rice) with protein and/or fat (as in say a beef curry and rice meal) the total GL of the meal is lowered.