Study Comparing Health Benefits of Breads Raises Further Questions

07 Jul 2017 --- Following a study comparing differences in how processed white bread and artisanal whole-wheat sourdough affect clinically relevant parameters and the microbiome, the Real Bread Campaign has renewed its call for more research into the health effects of different types of loaf production. 

Published in Cell Metabolism, the trial involved two groups of ten people, all of whom normally consumed about 10 percent of their calories from bread. Half were assigned to consume an increased amount of processed, packaged white bread for a week — around 25 percent 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.

The researchers monitored health effects, including wakeup glucose levels; levels of the essential minerals calcium, iron, and magnesium; fat and cholesterol levels; kidney and liver enzymes; and several markers of inflammation and tissue damage. The investigators also measured the makeup of the participants’ microbiomes before, during and after the study.

According to the researchers, gut microbiota composition remained person-specific throughout the trial, and there was a small but “statistically significant” interpersonal variability in the glycaemic response to the two loaf types. 
 
“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 of 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.”
 
Avraham Levy, a professor in the Department of Plant and Environmental Sciences and another coauthor, adds a caveat to the study: “These experiments looked at everyone eating the same amounts of carbohydrates from both bread types, which mean that they ate more whole-wheat bread because it contains less available carbohydrates. Moreover, we know that because of its high fiber content, people generally eat less whole-wheat bread. We didn’t take into consideration how much you would eat based on how full you felt. So the story must go on.”

In response to the study, the Real Bread Campaign has said that the key issue it has “with taking this study as anything more than an interesting anomaly” are that the sample size was very small and that the study only lasted one week.

“Its results and conclusions are contrary to the widely accepted evidence that loaves made from higher extraction flours are healthier than those made from highly-refined white flour, and also to research on the potential benefits of sourdough fermentation, some of which is cited in the study itself.” 

Moreover, two of the researchers act as paid advisors to a company that sells personalized nutrition advice “based on your unique biome.”

On its website, the Real Bread Campaign states that the study does, however, further underline the “need for much more research into the effects of different ways of producing a loaf. Finding ways to make loaves that are healthier and that more people can enjoy is in the interests of the industrial millers and bakers.”