The article “The behavior of dietary fiber in the gastrointestinal tract determines its physiological effect” was published in Critical Reviews in Food Science and Nutrition. Capuano reviews the various definitions used to describe dietary fiber and notes they all refer to carbohydrate polymers that are not digested or absorbed in the upper human intestine but differ in chemical composition and distribution of monosaccharides, physiological health benefits, or analytical method based characterization. Additional properties that can impact dietary fiber properties include particle size, solubility, water absorption/desorption, and viscosity.
Following a brief review of digestion physiology, Capuano reviews the modifications that occur to dietary fibers in the digestive tract that affect their behavior and physiological benefits.
- Formation of complexes between dietary fiber and phenolic compounds in the mouth and small intestine that result in variable release and bioavailability of phenolic compounds.
- Reduced bioavailability of intracellular compounds due to cell wall material providing a structural barrier during digestion.
- Increased viscosity/gelling in the stomach and small intestine.
- Inhibition of the enzymes and small intestine that alter macronutrient hydrolysis.
- Emulsion stabilization/destabilization that affects lipid digestion.
- Mineral and bile salt sequestration.
- Increased bacterial growth and production of short chain fatty acids in the large intestine.
- Increased peristalsis and mucus production in the large bowel resulting in reduced transit time.
The author notes that structure-function relationships explain some of the physiological effects of dietary fibers and suggests understanding the molecular structure of dietary fibers may predict physiologically relevant outcomes. The author states “Finally, in designing in vitro experiments it is time to move toward more realistic experimental settings where the effect of DF is investigated in relation to the food matrix/meal with which it is provided. This will represent a contribution to the shifting from the reductionist approach to nutrition where a food is merely regarded as the sum of its nutritive components to a more integrated food-based approach where the effect of the interactions between individual components and thus of the foods as a whole is considered.” Nonetheless, diets rich in dietary fiber appear to have health benefits that may related to changes to digestive processes rather than intrinsic nutritional properties or the elicitation/triggering of specific biological activities.
Additional information on the recommended daily intake for dietary fiber and several fibers that can be added to the diet is available here.