Wonder bread.   Whole-wheat.  Gluten-free.  Sourdough.  Which is healthiest?   

It depends.  On your gut microbiome.

A new study published this month in Cell Metabolism and co-authored by DayTwo’s founders and Weizmann Institute Scientists Eran Segal and Eran Elinav, report the results of a comprehensive, randomized trial comparing differences in how processed white bread and artisanal whole-wheat sourdough affect the body.

The study included 20 participants, all of whom normally consumed about 10% of their calories from bread. Half were assigned to consume an increased amount of processed, packaged white bread for a week—around 25% of their calories—and half to consume an increased amount of whole-wheat sourdough, which was baked especially for the study and delivered fresh to the participants. After a two-week washout period, the diets for the two groups were reversed.

Before the study and throughout study duration, participants’ health effects were monitored, including wakeup glucose levels; levels of calcium, iron, and magnesium; fat and cholesterol levels; kidney and liver enzymes; and several markers for inflammation and tissue damage.

The study also measured the makeup of the participants’ microbiomes before, during, and after the study.

“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,” says Eran Segal, a computational biologist at the Weizmann Institute of Science and one of the study’s senior authors. “We looked at a number of markers, and there was no measurable difference in the effect that this type of dietary intervention had.”

Based on some of their earlier work, however, which found that different people have different glycemic responses to the same diet, the investigators suspected that something more complicated may be going on: Perhaps some of the people in the study were responding better to one type of bread, and some to the other. A closer look indicated that this was indeed the case. About half the people had a better response to the processed, white-flour bread, and the other half had a better response to the whole-wheat sourdough. The lack of differences were only seen when all findings were averaged together.

“The findings for this study are not only fascinating but potentially very important, because they point toward a new paradigm: Different people react differently even to the same foods,” says Eran Elinav, a researcher in the Department of Immunology at the Weizmann Institute and another of the study’s senior authors. “To date, the nutritional values assigned to food have been based on minimal science, and one-size-fits-all diets have failed miserably.”

He adds: “These findings could lead to a more rational approach for telling people which foods are a better fit for them, based on their microbiomes.”



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