Gut composition affects whether white or brown bread is healthier, say researchers

By Sally Robertson, B.Sc.Jun 7 2017

Whether or not whole wheat bread is better for you than white bread is not as clear-cut as people generally believe and depends somewhat on an individual’s gut microbiome, say researchers.

Credit: George Dolgikh/Shutterstock.com

Scientists from the Weizmann Institute of Israel have carried out a comprehensive, randomized trial including 20 healthy individuals to compare the effects of wholegrain sourdough and industrially produced white bread on the body.

Specifically, they looked at the health impact of eating the two types of bread on an individual’s microbiome – the collection of bacteria and other gut flora in the body – as well as the effect on levels of blood glucose, fat, cholesterol, inflammation markers, kidney and liver enzymes and minerals.

For one week, ten individuals ate processed white bread containing refined wheat flour, preservatives and emulsifiers and the other ten ate freshly baked, whole wheat sourdough. This was followed by a two-week period of eating no bread and then the groups switched bread type.

As reported in Cell Metabolism, when the results for all participants were pooled together, the type of bread itself had no significant effect on health.

The initial finding, and this was very much contrary to our expectation, was that there were no clinically significant differences between the effects of these two types of bread on any of the parameters that we measured,"

Senior author, Eran Segal

The two bread types also did not appear to have any difference in effect on the gut microbiome. However, on taking a further look at the results, the team found that there were differences in the way individuals responded to the different breads.

Half had a higher blood glucose response to the white bread and half had a higher blood glucose response to the sourdough. Furthermore, the researchers found they were able to predict which bread participants would respond better to, based on the composition of their gut microbiomes. It was only when the results were averaged together that the differences did not show.

Senior co-author, Eran Elinav, says the findings are both fascinating and potentially important because until now, nutritional values assigned to foods have been based on a one-size-fits-all approach, when, in fact “different people react differently, even to the same foods."

"These findings could lead to a more rational approach for telling people which foods are a better fit for them, based on their microbiomes," Elinav concludes.