Whole wheat diets may reduce the risk of inflammatory bowel disease

Enriching the diet with wheat fiber protects mice against intestinal inflammation, according to a study published by researchers in the Institute for Biomedical Sciences (IBMS) at Georgia State University. The finding helps explain why incidence of inflammatory bowel disease (IBD) has increased, and suggests eating whole wheat foods may reduce one's risk of developing it.

The work, which is reported in two research papers - in the journals Science Advances and Mucosal Immunology - investigated the impact of wheat fiber, which is present in whole wheat and whole grain breads but mostly absent in "white breads" and other products made from refined flours.

The researchers found that metabolism of wheat fiber by intestinal bacteria generated bioactive anti-inflammatory metabolites, including polyphenols, which reprogrammed intestinal immune cells to suppress inflammation, protecting mice from developing acute and chronic intestinal inflammation.

Changes in food production, especially the increased use of highly refined wheat products, have reduced dietary consumption of wheat fiber, potentially contributing to the increased prevalence of IBD. The findings, if true in humans, suggest that choosing whole wheat breads, pastas and other flour-based products, rather than white versions, may reduce one's risk for developing IBD. Furthermore, the studies suggest that adding wheat fiber to processed foods can also confer this benefit.

Wheat fiber is but one of many fibers that is frequently not consumed in adequate amounts in developed countries. Indeed, most people in developed countries don't meet the recommendations of health organizations to consume a minimum of 25 to 38 grams of fiber per day. These recommendations are based on evidence that consumption of plant-based foods naturally rich in fiber is associated with good health and an array of animal studies showing that enriching diets with fiber promotes beneficial health outcomes. 

Yet, such studies largely focused on fibers, such as psyllium, derived from Plantago seeds, and inulin, derived from chicory root, that have not historically been a major component of diets in the West. Thus, the observation that wheat fiber, historically abundant in Western diets, conferred such benefits is especially relevant to appreciating the importance of dietary fiber on gut health. Furthermore, the mechanism by which wheat fiber acts is highly distinct from other fibers. Specifically, wheat fiber did not act by increasing short-chain fatty acids, as soluble fibers do, but by releasing bound polyphenols when digested by gut bacteria. Indeed, wheat fiber only provided a benefit to mice when they contained a microbiota capable of catabolizing wheat fiber to release polyphenols.

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. Furthermore, they suggest that incorporating wheat fiber into processed foods may make them healthier."

Andrew T. Gewirtz, senior author of the study and a Regents' Professor in the Institute for Biomedical Sciences at Georgia State

"The chemistry of dietary fibers can be pretty complicated," said Seong-eun G. Kim (Ph.D. '25), first author of the study, a recent IBMS Ph.D. graduate and now a postdoctoral fellow at Weill Cornell Medicine. "But intestinal bacteria are quite good at metabolizing them and the immune system is a major beneficiary."

"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 added. "Better understanding of these molecules should ultimately enable production of healthier processed foods but, meanwhile, choosing whole wheat and whole grain breads and having one's diet include an assortment of fruits and vegetables seems a good idea."

Additional authors of the Science Advances study include Rachael Ott, Alexis Bretin, Hirohito Abo, Yanling Wang, Yadong Wang and Vu L. Ngo of the Institute for Biomedical Sciences at Georgia State; Shawn Winer of the University of Toronto; Daniel A. Winer of the University of Toronto, Buck Institute for Research on Aging and Toronto General Hospital Research Institute (TGHRI), University Health Network; Lavanya Reddivari of Purdue University; Stacey L. Heaver and Ruth E. Ley of the Max Planck Institute for Biology; and Michael Pellizzon of Research Diets Inc.

The study was funded by the National Institutes of Health (NIH) and a Crohn's and Colitis Foundation Research Fellowship Award.