You can either make your own sourdough bread using a sourdough starter or buy a loaf at the local bakery. Note that all rye breads made with whole grain rye are by nature sourdough. (For bread to rise, yeast reacts with the gluten in the wheat. Rye doesn’t contain enough gluten to rise with yeast, so sourdough starter is used to get the same effect.)
Some breads are called sour breads because they have sour flavoring agents added. While it’s possible they could have a beneficial effect on blood sugar (say, if the souring agent is vinegar), they haven’t been studied as sourdough bread has.
Sourdough bread has a distinctive tart taste, but you can use it whenever you might use regular bread. Try it for sandwiches and hamburgers, as a crunchy accompaniment to al dente spaghetti and sauce, or to go with soup.
Perfect Portion: 1 ounce (30 g)
A serving is about the size of one small slice, depending on the brand. Eat two slices, as you would in a sandwich, and the bread becomes a medium-GL food — still reasonable.