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TR90 In addition to the effect of dietary fiber on satiation, which appears to be driven primarily by its ability to dilute the energy density of the diet and exploit mechanical threshold and sensory mechanisms of food intake regulation, dietary fiber also has the capacity to affect satiety. Meal-induced signals of satiety are generated both pre- and postabsorptively. However, preabsorptive satiety-related mechanisms, especially those at the level of the small intestine, are essential in the induction and maintenance of satiety (Rolls 1995b). Therefore, prolonging the intestinal phase of nutrient processing and absorption is likely to intensify satiety and aid in food intake control.

Incorporation of viscous fibers into a mixed meal at sufficient levels increases the viscosity of GI contents. Increasing viscosity of intestinal contents slows gastric emptying and small bowel transit, interferes with the mixing of food stuffs and digestive enzymes, disrupts micelle formation, and alters diffusion and interaction of nutrients with mucosal surface (Schneeman and Tietjen 1994, Vahouny et al. 1988). The combination of these events results in slowed fat and carbohydrate absorption, which prolongs the period in which these nutrients can interact with preabsorptive mechanisms of satiety. Because the small intestine is the primary site for fat-induced satiety, delaying fat absorption and increasing intestinal exposure to fat should intensify its effect on satiety. Indeed, infusing equivalent amounts of fat into the duodenum of rats at a slow rate (extended exposure) compared with a faster rate (time-reduced exposure), resulted in reduced average daily energy intake, altered patterns of feeding and reduced body weight gain (Burton-Freeman and Schneeman 1996). The concept that intraluminal fat exposure is related to satiety and food intake control may illuminate the reason(s) why diets that are low in fat (often those prescribed for the management of diseases such as obesity, cardiovascular and diabetes) are difficult to adhere to long term (Anderson and Gustafson 1989). Diets low in fat and energy are associated with chronic sensations of hunger, which may be due in part to less fat in the intestine available for stimulation of mechanisms of satiety. Therefore, slowing dietary fat absorption to enhance satiety, especially when fat levels are low, may have a significant effect on the overall therapeutic benefit of low fat diets because adherence may be maintained long term. If inclusion of viscous type fibers in low fat diets will effectively slow fat absorption and impart a greater sense of satiety, this would be a reasonable dietary approach to aid in successful adoption of low fat diets. We recently investigated this potential interaction of fat and fiber in meals to influence postmeal satiety. The data indicated that in women, incorporation of foods rich in viscous fibers into mixed low fat meals (20% energy from fat) resulted in suppressed sensations of hunger and enhanced postmeal satiety compared with an equally energetic and palatable low fat, low fiber meal. Moreover, the satiety response to the low fat, high fiber meal was similar to that of a high fat (38% energy from fat), low fiber meal with similar energy content. Analysis of plasma cholecystokinin (CCK) concentrations in response to these meals showed a similar pattern, in that elevated and sustained CCK concentrations were observed with both the low fat, high fiber meal and the high fat, low fiber meal. Others have shown a similar sustained CCK response above baseline CCK concentrations when viscous fibers were included in a low fat meal (Bourden et al. 1999). Because CCK release is sensitive to fat in the small intestine and is a proposed mediator of fat-induced satiety, the results from these studies are consistent with the idea that delaying fat absorption from the intestine can improve satiety of meals lower in fat.
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