Whether standard white bread or an artisanal sourdough loaf is healthier depends on the microbes living in a person’s intestines, a new study suggests.

Averaging results from 20 people who ate white and whole-wheat sourdough bread for one week each, researchers found no difference in people’s response to the breads, which includes changes in blood sugar levels.

But when researchers examined each person individually, a different pattern emerged: Some people’s blood sugar levels climbed more after eating the white bread than after the sourdough. For others, the opposite was true, the team reported in the journal Cell Metabolism.

The results are part of a growing body of evidence that nutrition advice should be personalized. Previous work by the same group at the Weizmann Institute of Science in Rehovot, Israel, showed that responses to eating a variety of foods vary considerably from person to person.

Research with mice also suggested that genetic differences may cause one strain of mouse to gain weight on a diet that helps another strain slim down.

In the new study, researchers Eran Elinav, Eran Segal and colleagues analyzed the study participants’ genetic makeup along with the mix of microbes in stool samples from each person. The team could predict a participant’s response to the two types of bread based only on which microbes were present in the stool, particularly the amounts of two types of bacteria.

The researchers don’t yet know how the bacteria change blood sugar.

Science News