Previous research from the two largest cohorts to date has shown that diet is one of the primary factors involved in gut microbiome variation among healthy individuals. Regarding bread type, little is known about how interpersonal variation affects clinical and microbiome-related responses.

A new study, led by Dr. Avraham Levy, Dr Eran Elinav and Dr. Eran Segal from the Department of Computer Science and Applied Mathematics at the Weizmann Institute of Science in Israel, has found that the effects of bread type on postprandial glycemic responses are associated with individuals’ gut microbiomes.

The researchers performed a randomized crossover trial of two 1-week-long dietary interventions including consumption of either traditionally made sourdough whole wheat bread or industrially made white bread, separated by a 2-week-long washout period. Healthy participants were randomly assigned to two sequence groups: white bread consumption followed by sourdough bread consumption (n = 10), or sourdough bread consumption followed by white bread consumption (n = 10). Blood clinical parameters, anthropometrics, oral glucose tolerance test, and gut microbiome composition and function were measured at baseline, after the first intervention period, after the washout period, and at the end of the second intervention period.

Although the one-week dietary intervention of bread consumption, independent of bread type, affected multiple metabolic and clinical markers, at the end of the study bread type had no significant differential effects on multiple clinical parameters.

Overall gut microbiota species composition remained stable (only underwent minor alterations) throughout the entire study. These results contradict prior studies (here; here) that have found even short-term dietary interventions result in significant and reproducible alterations of the gut microbiome composition. No significant differences in treatment effects between white and sourdough bread were found for functional properties of the gut microbiome.

The researchers also found that the effect of each bread was person-specific as there was high interpersonal variability in the postprandial glycemic response to each kind of bread. About half the people had a better response to the white bread, and the other half had a better response to the sourdough bread. These findings were in agreement with some previous work from the same group, which found that different people have different glycemic responses to the same food. Besides this, the glycemic response to bread type was also microbiome associated as it was predicted for each subject using only microbiome data.

In conclusion, the glycemic response to bread type (sourdough whole wheat bread and white bread) is person specific and related to the gut microbiome. Further research is needed in order to explore to what extent responses to nutritional interventions can be predicted based on the gut microbiome.

Learn more about the potential role of gut microbiota in personalized nutrition in this interview with Niv Zmora, co-author of the study covered in this post.



Korem T, Zeevi D, Zmora N, et al. Bread affects clinical parameters and induces gut microbiome-associated personal glycemic responses. Cell Metab. 2017; 25(6):1243-53. doi: 10.1016/j.cmet.2017.05.002.