How to influence the GI

You can change the GI rating of your food, or choose low GI versions of foods that may seem similar in other ways. Here are some of the variations:

Processing

This usually raises a food's GI. White bread has a higher GI than wholegrain.

Fibre

Soluble fibre lowers the GI. Foods like oats, legumes and fruit slow the digestion of starches and absorption of glucose into the blood. Porridge has a lower GI than Weet-Bix, which in turn is lower than Rice Bubbles.

Ripeness

Ripening raises the GI. A greenish banana will have a lower GI than a very yellow one.

Sugar

Surprisingly, table sugar has a medium GI. This is because it is made up of glucose (the highest possible GI) and fructose (low GI). Fructose is slowly converted to glucose, which lowers the GI compared to glucose and other foods like potatoes and white bread.

The trouble with sugar is not its GI rating. Sugar contains no other nutrients, it can cause tooth decay, and it often comes in high-energy foods.

Salt

This may raise the GI, because it speeds up the digestion.

Acidity

Lemon juice and vinegar lower the GI of a meal. You don't have to squeeze them over potato - just squeeze lemon over the veges or put vinegar or lemon juice on a salad, and when they get to your stomach they will slow down the absorption of starches in the potato anyway.

Food combinations

Fat and protein in foods lower the GI, by slowing digestion.

Individual variation

There is individual variation in the way people respond to a food (except when the GI is very low). This means a sandwich may sustain you for longer than it would your workmate.

Individuals also have varying blood glucose levels. You might find that sandwich is more sustaining today than another just like it tomorrow.

Food quantities

Don't forget this one. If you eat a lot of a particular low GI food, you will still raise your blood glucose levels significantly.

The GI is valuable, but a calculation called the Glycaemic Load (GL) is even more so. It takes the GI of a food and multiplies it by the grams of carbohydrate in a serving. This concept has not been sufficiently developed to be used routinely.