Høyer, 2000). After 2 to 6 weeks of treatment with 20 g/d of fructooligosaccharides or placebo, symptoms of irritable bowel syndrome improved more in the placebo group than in the fructooligosaccharide group; however, there was no difference between the groups after continuous treatment for 12 weeks.

Normalization of Blood Lipid Concentrations. Studies on the effect of inulin or oligofructose ingestion on plasma lipid concentrations have provided mixed results. Significant reductions in plasma triacylglycerol concentrations occurred with the intake of 10 g/d of inulin, particularly in those individuals with a baseline triacylglycerol concentration greater than 1.5 mmol/L (Jackson et al., 1999). The ingestion of 9 g/d of inulin significantly reduced plasma total cholesterol and triacylglycerol concentrations in young men (Brighenti et al., 1999). Nonsignificant changes in plasma total or high density lipoprotein (HDL) cholesterol and triacylglycerol concentrations were reported for individuals consuming 14 g/d of inulin (Pedersen et al., 1997) or 20 g/d of fructooligosaccharide (Luo et al., 1996). In young, healthy males, 15 g/d of nondigestible oligosaccharides (inulin or fructooligosaccharides) did not decrease blood lipids or affect glucose absorption compared to controls (van Dokkum et al., 1999).

Attenuation of Blood Glucose Responses. A placebo-controlled parallel study showed that a daily intake of 10 g of inulin significantly reduced fasting insulin concentrations (Jackson et al., 1999). Fasting blood glucose concentrations were significantly reduced by 15 mg/dL in type 2 diabetics who were fed 8 g/d of fructooligosaccharides (Yamashita et al., 1984). Daily intake of 20 g of fructooligosaccharides significantly decreased basal hepatic glucose production (Luo et al., 1996). No difference, however, was observed in the incremental area under the curve for glucose when individuals were fed 50 g of a rice-based cereal containing 0 or 9 g of inulin (Brighenti et al., 1999).

Other Potential Physiological Effects. An important effect of inulin intake is considered to be the production of Bifidobacteria. Bifidobacteria contain high amounts of β-fructosidase, which are specific for the β-(1,2) bond present in inulin and oligofructose. A number of studies in humans have shown that the ingestion of fructooligosaccharides leads to an increase in fecal Bifidobacteria (Bouhnik et al., 1996, 1999; Buddington et al., 1996; Tuohy et al., 2001; Williams et al., 1994). Bifidobacteria have been shown to promote beneficial health effects in animals (Grizard and Barthomeuf, 1999); however, potential beneficial effects in humans are not well understood.