1-Kestose Supplementation Increases Levels of a 5α-Reductase Gene, a Key Isoallolithocholic Acid Biosynthetic Gene, in the Intestinal Microbiota.

1-Kestose (kestose) is the smallest fructooligosaccharide component and shows a particularly high prebiotic function. Both kestose and the bile acid metabolite isoallolithocholic acid (isoalloLCA) are known to be beneficial for human health, especially in terms of immune homeostasis in the gastrointestinal system; however, the effect of kestose on the levels of microbial isoalloLCA producers remains to be clarified. IsoalloLCA is known to be produced by several members of the phylum Bacteroidota that carry the 5α-reductase (5AR) gene, a key isoalloLCA biosynthetic gene. Thus, we designed a specific primer set to detect the 5AR gene based on the consensus sequences of the genes from several isoalloLCA producers. Using real-time quantitative PCR with this primer set and fecal DNA samples, we compared the 5AR gene level (5ar-level) in the intestinal microbiota of a kestose-supplemented group (n=20) and a placebo group (n=16) before and after intake for 12 wk. The 5ar-level was significantly increased in the kestose-supplemented group (p=0.015), but not in the placebo group (p=0.379), indicating that kestose supplementation increased the 5ar-level in human intestinal microbiota. Our findings suggest that targeting functional gene levels could potentially be used to predict and understand the beneficial prebiotic effects associated with changes in gut microbiota.

Supplementation of 1-Kestose Modulates the Gut Microbiota Composition to Ameliorate Glucose Metabolism in Obesity-Prone Hosts.

Insulin resistance leads to the onset of medical conditions such as type 2 diabetes, and its development is associated with the alteration in the gut microbiota. Although it has been demonstrated that supplementation with prebiotics modulates the gut microbiota, limited evidence is available for effects of prebiotics on insulin resistance, especially for humans. We investigated the prebiotic effect of 1-kestose supplementation on fasting insulin concentration in obesity-prone humans and rats. In the preliminary study using rats, the hyperinsulinemia induced by high-fat diet was suppressed by intake of water with 2% (w/v) 1-kestose. In the clinical study using obese-prone volunteers, the fasting serum insulin level was significantly reduced from 6.5 µU/mL (95% CI, 5.5-7.6) to 5.3 (4.6-6.0) by the 12-week intervention with supplementation of 10 g 1-kestose/day, whereas it was not changed by the intervention with placebo (6.2 µU/mL (5.4-7.1) and 6.5 (5.5-7.6) before and after intervention, respectively). The relative abundance of fecal Bifidobacterium was significantly increased to 0.3244 (SD, 0.1526) in 1-kestose-supplemented participants compared to that in control participants (0.1971 (0.1158)). These results suggest that prebiotic intervention using 1-kestose may potentially ameliorate insulin resistance in overweight humans via the modulation of the gut microbiota. UMIN 000028824.