Generally, soluble fibers increase small intestinal mucin secretion by increasing the number of goblet cells in a viscosity-dependent manner. The present study aimed to examine the mechanism by which low-methoxyl pectin (LPC) affects mucin secretion in the small intestine. First, diets containing 50 g/kg of low-viscosity fiber (LPC, gum arabic, guar gum, low-molecular konjac mannan, arabinogalactan, sodium alginate) or high-molecular konjac mannan (KMH) were fed to Wistar rats for 10 d. Luminal mucin was greater in the LPC and KMH groups than in the fiber-free control group, but only the KMH group had more goblet cells in the ileum compared with the other groups. Next, Sprague-Dawley rats were fed LPC, KMH, or high-methoxyl pectin (HPC) diets (50 g/kg) for 10 d. The KMH and LPC groups, but not the HPC group, had greater luminal mucin than the control group, whereas jejunum Muc2 expression was higher only in the LPC group. Sprague-Dawley rats fed the LPC diet for 1 or 3 d had greater luminal mucin and jejunum Muc2 expression than those fed the control diet. In vitro studies using HT-29MTX cells showed that, of the various fibers studied, only LPC and HPC affected mucin secretion. Finally, Wistar rats were fed the LPC diet with or without neomycin in drinking water for 10 d; neomycin treatment did not compromise the effect of LPC on mucin secretion. We conclude that LPC does not affect the number of goblet cells but can interact directly with the epithelium and stimulate small intestinal mucin secretion.
Summary Resistant glucan (RG) is a water-soluble polysaccharide resistant to hydrolysis by digestive enzymes in the human gastrointestinal system. RG mixture (RGM) contains more than 75% RG as dietary fi ber and other saccharides. The effects of ingestion of 3.3, 6.6, and 13.2 g/d of RGM (containing of 2.5, 5.0, and 10.0 g/d RG as dietary fi ber) on the fecal properties and the frequency of defecation were investigated in 60 female volunteers with constipation. The study was designed as a randomized, single-blinded, and placebo-controlled parallel-group trial. Each subject consumed RGM or a placebo (digestible maltodextrin) for 2 wk. Questionnaire data on the effects on bowel movement were analyzed according to defecation days, defecation frequency, fecal volume, fecal shapes, fecal color, fecal odor, and fecal excretory feeling. The results showed signifi cant increases in defecation frequency (pϽ0.05), defecation days (pϽ0.05), and fecal volume (pϽ0.05) during the 13.2 g/d RGM ingestion period. The effects of RGM on defecation days and frequency showed a dose-dependent increase (pϽ0.05). These results suggested that the intake of RGM increased defecation days, defecation frequency, and fecal volume. In the gastrointestinal tract, RGM is useful as a water-soluble dietary fi ber for the improvement of bowel movements.
Resistant glucan mixture (RGM), a water-soluble dietary fiber produced by the random polymerization of glucose with activated carbon as a catalyst at a high temperature, has been recently developed by our group. There has been little physiological and safety research into RGM and therefore we now present our research into its safety. A reverse mutation assay indicated that RGM is not mutagenic either with or without metabolic activation. We conducted a 90-day subchronic oral toxicity study in rats. Male and female rats fed either a 3% or 5% w/w RGM diet had no muddy or watery stools, and there was no RGM-related death in any group. Although some parameters in the 3% and 5% w/w groups were significantly different from those in the control group, these changes were not due to any toxicity from RGM. The results indicated that the No Observed Adverse Effect Level (NOAEL) of RGM was 3.3 and 3.9 g/kg body weight (BW) per day in male and female rats, respectively. We then studied the gastrointestinal effects of RGM in healthy adult humans. Gastrointestinal symptoms, such as gurgling sounds, flatus and tenesmus, were mild and transient. In men and women, the maximum no-effect dose for diarrhea was more than 0.9 g RGM /kg BW. The results of our current safety assessment studies suggest that RGM is safe for human consumption.
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