Blood Sugar Improvements from Sourdough Bread

Part of the many fermented foods written in the article above, sourdough bread has many health benefits.

Terry Graham, a professor in human health and nutritional sciences at the University of Guelph, Ontario, Canada, lead a team of researchers who studied four types of breads to determine which had the most positive health effects when it comes to carbohydrate metabolism, blood sugar and insulin levels. The results were impressive. The results of these studies are not new. Some of the findings were first published in 2008.

While Professor Graham has retired he compared the way different types of bread were digested and assimilated into the body. Their results suggest that the grains used, the way they were milled and how the bread was made all affect the properties of a loaf. More importantly for fans of sourdough breads, they discovered that the long fermentation involved in baking with natural yeasts resulted in a loaf that was digested more slowly and caused less of a spike in blood sugar levels when it was eaten.

The research which took place in two studies over 7 years, focused on carbohydrate metabolism in humans and when his work turned to investigate the way carbohydrates are digested and assimilated, he chose bread as a high carbohydrate food to use in his trials. Bread is a simple food eaten by millions of people every day. But it may not be so simple. Professor Graham found out that bread is an extremely complex food and its properties change not only with ingredients but how it’s made, how it is baked and how it is served.

In the initial study, the research group chose four different breads to compare – white, whole wheat, whole wheat with barley and a white sourdough. Be aware that those breads (white, whole wheat, whole wheat with barley contain gluten. If you have gluten sensitivity those breads shouldn’t be consumed. Each member of a study group of volunteers was given one of the breads for breakfast, then monitored to see how their blood sugar and insulin levels responded over the course of the next few hours. At the start of the research the team expected that the whole wheat breads showed very similar responses, an initial spike followed by declining levels. The white sourdough bread showed the least pronounced response, with both blood glucose and insulin increases significantly lower than those seen followed a breakfast of non-sourdough bread. This is important because, from a health perspective, the aim is to keep blood sugar and insulin levels as close to normal as possible. The team also discovered that this response pattern was repeated when the volunteers were given lunch, not including bread, later in the day.

Following their first study, the team looked at other hormonal responses and included other breads in their trials. The results consistently showed sourdough to be associated with more moderate blood sugar response. Whole grain sourdough bread was found to show a similar response to white, while a sprouted grain sourdough showed the most positive response.

One the results of these studies were written and published, Professor Graham realized that fermented food from a range of cultures have been associated with good health.  He felt this had to do with the fermentation process, sourdough or otherwise which was important in promoting these responses.

One possibility was suggested by Steve Ciu, a food chemist of Agriculture Canada, is that the sourdough fermentation process was altering the structure of the starch in the bread. These changes mean that the starch would be digested and assimilated into the body more slowly, resulting in less pronounced responses in terms of blood glucose and insulin.  The surprising finding from the first study that white and whole wheat breads showed similar responses is probably because the whole wheat bread used was made from very finely ground flour to produce a texture in the baked loaf that is popular in North America and very similar to white bread.

Professor Graham speculated that for people at risk of or who have already been diagnosed with type 2 diabetes “could well benefit from having a sourdough bread rather than a normal yeast risen bread.”

The acids slow down the rate at which glucose is released into the blood stream and lower the bread’s glycemic index (GI), so it doesn’t cause undesirable spikes in insulin. They also render the gluten in flour more digestible and less likely to cause food intolerances.