Dietary Fiber Deprivation as a Mediator of Mucosal Barrier Dysfunction and IBD Trigger.

Many genetic factors have been associated with increased IBD susceptibility. However, these only explain a fraction of the disease risk that an individual with such a predisposition experiences. Environmental factors have been proposed to work in combination with host genetics to cause IBD. Diet and the normally beneficial community of bacteria that live in the human intestine are candidate “environmental” factors. The industrialized world, in which IBD is more prevalent, has experienced reduced consumption of dietary fiber–a term used to represent a group of complex carbohydrates abundant in vegetables and grains. Humans cannot directly digest fiber, so it transits to the distal intestine and is digested by gut bacteria. We have shown that a lack of dietary fiber causes gut bacteria to turn to a different source of carbohydrates to survive: protective intestinal mucus, which normally forms a barrier that keeps bacteria at a “safe distance” from host tissue. We propose that chronic or transient reductions in fiber trigger gut bacteria to erode the mucus layer, bringing them into proximity with the host and causing disease flares. Support for our model will allow us to explore dietary therapies to prevent IBD occurrence by reinforcing the integrity of the mucus layer.