Using Sourdough to Lower the Glycemic Index of Everyday Baked Goods

Both sweet and savory baked goods can pose health concerns for a variety of reasons:

  • When we eat baked goods made with white flour, blood sugar can spike upward after eating (the glycemic index, or carbohydrate component, is too high).
  • When we eat baked goods made with whole-grain flour, blood sugar remains relatively stable, but phytic acid stored in the bran may prevent us from absorbing minerals like iron, calcium, magnesium and zinc. Over time, this can lead to mineral depletion and bone loss.
  • When we bake with white or whole-grain flour and allow the batter to rest (soak) for a period of hours before baking, phytic acid is reduced, but grains become super-digestible and the result is a dramatic spike in blood sugar (the glycemic index is again too high).

     The problem, then, is circular in nature, with each solution creating a new problem. As a sourdough bread baker, I knew that sourdough creates an ideal carbohydrate: bread with a low glycemic index and almost no phytic acid due to the dough’s long rest before baking. So I wondered if I could use sourdough to improve the healthfulness of everyday baked goods by adding it to a batter and then allowing it to rest for a period of hours, just as when making sourdough bread. I believed this approach would lower the glycemic index of baked goods and reduce their phytic acid, a simple and elegant solution to the challenges listed above.

     This approach might be useful to those with insulin resistance, diabetes, or mineral deficiencies (like low calcium or iron), or to those who simply wish to lower the blood sugar impact of the baked goods they consume.

     The paragraphs that follow describe my tests and their promising results.

Test Results

     I conducted four series of tests centered around two recipes, one savory (buttermilk biscuits) and one sweet (banana muffins). In each case, I prepared the recipes using stone-ground flour, which may be important. The results of these tests were consistent and clear.

  • The top chart summarizes the results of adding sourdough to a savory biscuit recipe. The whole-wheat sourdough biscuit soaked for 24 hours caused only a modest rise in blood sugar and gave the most impressive result (see the red bottom line on the graph). These biscuits had the lowest blood sugar impact after 30 minutes, which is when blood sugar typically spikes upward, and provided the most substantial satiety and blood sugar stability. You can see this in the low arc, and the slow, steady blood sugar decline. This last factor illustrates why lessening the impact of blood sugar can also prevent hunger and overeating. In contrast, soaking a whole-wheat batter with buttermilk instead of sourdough causes blood sugar to spike and then plummet (see the blue top line).
  • The bottom chart summarizes the results of adding sourdough to a sweetened banana muffin. The whole-wheat sourdough muffin soaked for 12 hours gave the best result (see the blue line on the graph). These muffins caused a moderate increase in blood sugar, coupled with sustained blood sugar levels over a full two hours and a slow, steady decline. Interestingly, in this experiment the same sourdough batter soaked for 24 hours(see the yellow line) yielded the worst results. More research would be needed to understand why.
  • While not illustrated in the charts, I conducted further tests to determine the quantity of sourdough needed to achieve these same results. Using just one quarter of the amount of sourdough worked, proving that where a sour taste is not desired, less sourdough can be used. (I have so far experimented with using as little as 1 ounce of sourdough starter to 31 ounces of savory biscuit dough to achieve this same result.)
  • In each case, unsoaked whole-wheat batters traced a gentle glycemic curve but, without soaking, phytic acid in the finished baked good may remain an issue.
  • Test results also indicated that the inclusion of sourdough in a batter–but without a soak–has no impact on the glycemic index. A soak is required, and soaking time seems to matter.

Conclusion

     These tests demonstrated that we can indeed use sourdough to reduce the glycemic index of everyday baked goods and to reduce their phytic acid, as long as the flours we use are stone-ground (see below) and as long as we allow the batter or dough to rest before baking. In these experiments, a 12-hour sourdough soak gave the best results in sweetened baked goods. For savory baked goods, a 24-hour soak worked better. Soaking with buttermilk, and without sourdough, caused blood sugar to spike dramatically and then plummet downward. In recipes where a sour taste is not needed, sourdough can comfortably be cut to one-quarter of the amount initially tested.

     There is more to learn. Most importantly, what is the ideal amount of sourdough and length of soaking time needed to give the optimum result? Also, studies by others show that stone-ground flour is necessary for lowering blood sugar. My own tests confirmed this, but a closer look is warranted. Finally, in what other varieties of baked goods can we use sourdough to lower glycemic response, and where is this a palatable approach and where is it not? From a culinary perspective, I have used sourdough in other sweetened baked goods (cakes–including chocolate cakes, cookies, cornbread, muffins and quick breads) and achieved a good result, often better than without. On the savory side, I have made sourdough pizza, pancakes, English muffins, and a variety of breads. All this is to say that sourdough offers delicious potential to lower the glycemic index of everyday baked goods.

Copyright 2013, Ellen Arian, Ellen's Food & Soul