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What Bread Is Best for Your Microbiome?

What bread is best, white bread or sourdough? The balance of microbes in your digestive tract determines which bread raises blood sugar more quickly.

Previous research has identified bread, especially bread made from refined white flour, as a food that can raise blood sugar and insulin levels rapidly. This is considered a food with a high glycemic index. Over time, a diet that raises blood sugar too readily has the potential to contribute to a variety of health problems, including diabetes, obesity and heart disease. So what bread is best?

It seems that the obvious solution to a diet with high-glycemic index bread would be a switch to wholesome whole-grain bread. Israeli scientists have found, however, that the obvious solution isn’t necessarily correct.

What Bread Is Best for Blood Sugar?

Twenty volunteers participated in a study comparing industrial white bread made from refined flour to sourdough bread baked of stone-milled whole-wheat flour in an artisanal bakery. The investigators chose sourdough as one of the options because it may raise blood sugar less than ordinary bread. The volunteers were randomly assigned to eat one type of bread during the first week and the second type during another week. In between, there was a break period of two weeks to “wash out” any effects.

No Overall Differences in Blood Sugar:

The scientists found no significant differences in wake-up glucose responses to the two different types of bread. They also detected no differences between groups on the oral glucose tolerance test, a way of determining blood sugar response to food. They theorize that the differences between individual responses averaged themselves out in the groups.

What Bread Is Best Depends on Your Gut Microbes:

About half the participants had higher blood sugar levels on the white bread diet; the other half had their blood sugar rise more on the sourdough bread diet. The scientists also studied the volunteers’ intestinal microbes. Variations in the abundance of certain species were linked to the different glycemic responses to the two types of bread.

Korem et al, Cell Metabolism, June 6, 2017 

Learn More:

We interviewed one of the senior researchers on this project about related work a few years ago. That experiment determined that “glycemic index” is not one-size-fits-all. Eran Segal, PhD, explained it to us in Show 1017: How to Avoid Weight Gain Over the Holidays.

If you would like guidance on fixing food that is more likely to be low in glycemic index, you’ll find tips in our book, Recipes & Recipes from The People’s Pharmacy.

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies..
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