What type of bread is less likely to cause blood sugar spikes?

Whole Grain. Compared to white flour, whole grains take longer for the stomach & intestines to break down into sugar, and so the sugar is absorbed more gradually into the blood stream and is less likely to cause a spike. A 15 gram whole grain slice will put just as much sugar into the blood as a 15 gm slice of white bread, but spread out over a longer period of time, and so requires lower Insulin levels.