Inulin and oligofructose as dietary fiber: A review of the evidence

This critical review article examines the composition and source of inulin and oligofructose, the physiological effects of their consumption, and how these materials relate to the concept of dietary fiber. Inulin and oligofru ctose are fructans extracted on a commercial basis from the chicory root. I nulin has been defined as a polydisperse carbohydrate material consisting m ainly, if not exclusively, of beta (2-1) fructosyl-fructose links ranging f rom 2 to 60 units long. Native chicory inulin has an average degree of poly merization (DP) of 10 to 20, whereas oligofructose contains chains of DP 2 to 10, with an average DP of 4. While a universally accepted definition for dietary fiber does not exist, i t is generally agreed that this term includes saccharides (+ lignin) that a re not hydrolyzed or absorbed in the upper part of the gastrointestinal tra ct. These materials reach the colon, where they may be totally fermented, p artially fermented, or remain unfermented. In addition, fibers contribute t o fecal bulking. Inulin and oligofructose are not digested in the upper part of the gastroin testinal tract or are they absorbed and metabolized in the glycolytic pathw ay, or directly stored as glycogen like 'sugars' or starches. None of the m olecules of fructose and glucose that form inulin and oligofructose appear in the portal blood. These materials are quantitatively fermented by the mi croflora of the colon; further, it has been demonstrated that this fermenta tion leads to the selective stimulation of the growth of the bifidobacteria population. After reviewing their chemistry, origin, and physiological effects, it is t he opinion of the authors that inulin and oligofructose are dietary fiber. They share the basic common characteristics of dietary fibers, that is, sac charides of plant origin, resistance to digestion and absorption in the sma ll intestine, and fermentation in the colon to produce short-chain fatty ac ids that are absorbed and metabolized in various parts of the body. Moreove r, this fermentation induces a bulking effect.