If you are concerned about your health, you should also think about what your gut bacteria consume. Dietary fiber is a key source for their nutrition. Thus the quantity of fiber in your diet influences your weight, blood glucose level and sensitivty to insulin is well-established. The latest research from Sahlgrenska Academy shows that colonic health is also affected.

Cell Host & Microbe recently published a study by scientists at Sahlgranska Academy to clarify the mechanisms for how fiber contributes to colonic health. Meanwhile, many people in contemporary society appear to be heading in a different direction altogether.

"Average fiber consumption has declined drastically in developed countries over the past few decades," Fredrik Bäckhed, Professor of Molecular Medicine, says. He studies the role of gut bacteria in metabolic disorders.

Various kinds of fiber are found in fruit, legumes, vegetables and whole grain products. Insufficient fiber consumption combined with a high-fat, high-carbohydrate diet is associated with a greater risk of inflammatory bowel disease, weight gain and diabetes.

Mice in the current study were put on a low-fiber diet. They developed defects in the inner colonic mucus layer after only three days characterized by increased bacterial penetrability, a potential risk for inflammatory bowel disease and other disorders.

"Our results demonstrate that the inner mucus layer separate gut bacteria from the body's cells," Gunnar C. Hansson, Professor of Medical and Physiological Chemistry and director of the study, says. "We clearly illustrated the rapid, process by which the mucus layer responds to dietary modifications and subsequent bacterial changes."

In a second experiment, the mice fed fiber-depleted diet received a transplant of gut bacteria from a normally fed animal and regained some of the lost protective effect.

A dietary supplement of friendly bifidobacteria stimulated growth of the mucus layer but did not prevent bacteria in the gut microbiota from approaching the body's cells. A supplement of inulin, a type of dietary fiber, addressed the latter problem but not the former.

"Low-fiber diets alter bacterial composition and influence what they produce," Professor Hansson says. "The result can be greater penetrability that affects the body's cells."

The researchers believe that fiber supplements as a method of treatment need to be investigated further. Simply enriching food with refined fiber is not recommended before more has been learned about its complex interplay with food, bacteria and the body's cells.