What ingredients are added to white bread to reduce its Glycaemic Index value?

Traditionally white bread has a high Glyceamic Index (GI) value but there are a range of white breads now available in the supermarket with added cereal or vegetable fibre and some of these may have a lower GI than standard white bread.

The GI Value of the bread can be reduced by the addition of resistant starch, soy flour and vegetable gum (guar gum), which subsequently means an increase in the fibre content of the bread. For example, Bakers Delight Lo-GI bread has a fibre content of 8.3g per 80g serving (2 slices) and according to the label this bread has a GI of 52.
In comparison whole grain varieties of bread typically have a GI in the range of 46-53.