The behavior of dietary fiber in the gastrointestinal tract determines its physiological effect.

A diet rich in dietary fiber (DF) is considered healthy and recommended dietary intake of DF is established all over the world. The physiological effect of DF is mostly related to its behavior during digestion. In this review, the behavior of DF in the human digestive tract is discussed and linked to its physiological effect with special attention to four aspects of such behavior: (i) the modulation of bioavailability by the plant cell walls, (ii) the effect of DF on the rheological and colloidal state of digesta, (iii) the binding of DF with phenolic compounds, bile salts, mineral ions, and digestive enzymes, and (iv) DF fermentation in the large intestine and the corresponding effect on microbiota composition. It is stressed that the detailed chemical characterization of DF is crucial to explain its effect on health and that DF behavior in the digestive tract can be modulated by interactions with other food and meal components so that information of the bare content in DF of food is not sufficient to predict its physiological effect.