Psyllium shifts the fermentation site of high-amylose cornstarch toward the distal colon and increases fecal butyrate concentration in rats.

We examined the combination effects of psyllium (PS) and resistant starch on large bowel short-chain fatty acids (SCFA). Rats were fed one of the following four diets: low amylose (LAS) or high amylose cornstarch diets (HAS, 50 g/kg diet) with or without 15 g PS/kg diet (LAS/PS and HAS/PS diets). HAS and/or PS were substituted for the same amounts of LAS in diets. Cecal butyrate concentrations were significantly higher in rats fed the HAS and HAS/PS diets than in those fed the LAS and LAS/PS diets. However, butyrate and total SCFA concentrations in rats fed the HAS diet decreased along the length of the colon and fecal butyrate concentration was reduced to one-third of that in the cecum. In contrast, the HAS/PS diet maintained higher butyrate concentrations throughout the large bowel. Fecal butyrate concentration in the HAS/PS diet-fed group significantly exceeded the sum of the concentrations in rats fed the LAS/PS and HAS diets. PS supplementation to the HAS diet significantly increased fecal starch excretion by 10 fold compared with that of rats fed the HAS diet. There was a positive correlation between fecal butyrate concentration and fecal starch excretion (r = 0.709, P < 0.0001). In a further experiment, ileorectostomized rats were fed the HAS and HAS/PS diets. From the difference in fecal starch excretion between normal and ileorectostomized rats, starch degradation by large bowel microflora in rats fed the HAS and HAS/PS diets was deduced to be 96% and 63%, respectively. These findings support the hypothesis that PS may delay the fermentation rate of HAS in the cecum and shift the fermentation site of HAS toward the distal colon, leading to the higher butyrate concentration in the distal colon and feces.