when individuals with Type 2 diabetes consume higher fiber diets (Anderson and Ward, 1979). The beneficial physiological effects of viscous fibers on blood glucose concentrations have been consistently demonstrated for over 25 years and are supported by more mechanistic studies.
Hydrolysis reduces viscosity of guar gum and mixed linkage Î²-glucan (Jenkins et al., 1978; Wood et al., 1994) and hydrolyzed versions are now available because the lower viscosity may increase potential for additional food uses. However, what data exist on the physiological differences seen when polymeric chain length and viscosity are reduced suggest that the glycemic and cholesterol-lowering effects of fiber may be reduced or lost (Favier et al., 1997; Jenkins et al., 1978; Lund et al., 1989; Wood et al., 1994). Therefore, the advantages of improved palatability and ease of use must be weighed against potential loss of physiological effect for fibers that have a shorter chain length and reduced viscosity.
A fiber-rich diet has been suggested to be an important factor in weight maintenance and the treatment of obesity (Appleby et al., 1998; Burley et al., 1993; Miller et al., 1994), although the significant changes in upper gastrointestinal tract function are difficult to consistently measure. Diets high in fiber are associated with slower stomach emptying, which induces a short-term increase in satiety (Roberfroid, 1993). This may modulate caloric intake and the rate of nutrient absorption. In addition, the reduced caloric density of diets rich in fiber has been suggested to be an asset in weight maintenance. Diets higher in fiber are just one aspect of the treatment of obesity, and at this time, measurable effects attributable solely to fiber are insufficient to designate fiber as a beneficial physiological effector of body weight.
There are several other potential beneficial effects of fiber and fiber-like materials for which additional data are needed before the benefits can be substantiated. For example, some preliminary observational evidence suggests fiber may protect against duodenal ulcers (Aldoori et al., 1997) and gastric cardia cancer (Terry et al., 2001). Animal experiments have suggested a role of various fibers on intestinal immune function (Field et al., 1999; Lim et al., 1997), although human studies are lacking. As a result of fiber serving as substrate for bacteria in the large intestine, changes in the spectrum and mass of bacteria in the intestine have been a topic of discussion for some time (Roberfroid, 1993). As these changes are more thoroughly understood, the use of fibers to modify fecal and colonic bacteria, much like the suggested use of probiotics, may be possible.