Whole wheat bread has long been positioned as the healthier alternative to white bread, but new research offers a clearer explanation for why that may be the case.
A study published in Science Advances found that wheat fiber helped protect mice against intestinal inflammation by interacting with gut bacteria and the immune system. The findings suggest that choosing whole wheat foods over refined grain products could play a role in supporting gut health, though researchers caution that the results have not yet been confirmed in humans.
The research was conducted by scientists at Georgia State University and also reported in the journal Mucosal Immunology.
Researchers examined how wheat fiber, which is abundant in whole wheat products but largely removed during the refining process, affects the gut. They found that when intestinal bacteria broke down wheat fiber, they released bioactive compounds, including polyphenols, that influenced immune cells in ways that reduced inflammation.
“These findings support the hypothesis that the widespread adoption of bran removal in generating wheat-based foods has contributed to increased incidence of chronic inflammatory diseases,” said Andrew T. Gewirtz, senior author of the study and a Regents’ professor at Georgia State.
Unlike some other types of fiber, wheat fiber did not appear to work primarily by increasing short-chain fatty acids. Instead, its benefits were linked to how gut microbes processed it into compounds that helped regulate immune responses.
The effect also depended on the presence of specific gut bacteria. Mice only experienced protection against inflammation when their microbiome was capable of breaking down wheat fiber to release these compounds.
“The chemistry of dietary fibers can be pretty complicated,” said Seong-eun G. Kim, the study’s first author. “But intestinal bacteria are quite good at metabolizing them and the immune system is a major beneficiary.”
The findings may help explain broader dietary trends. As food production has shifted toward more refined grain products, overall intake of wheat fiber has declined. Researchers suggest this change could be one factor contributing to rising rates of inflammatory bowel diseases, though the study does not establish a direct cause-and-effect relationship in humans.
The results also highlight a broader point about fiber. Different types of fiber can have different effects in the body, depending on how they are processed by gut bacteria.
“Indeed, the more we study dietary fibers, the more we appreciate that they are highly diverse compounds with fibers from distinct plants having distinct health-promoting impacts,” Gewirtz said.
While more research is needed in humans, the findings support existing dietary guidance to include more fiber-rich foods, such as whole grains, fruits and vegetables.
This research was funded by the National Institutes of Health and the Crohn’s and Colitis Foundation.