Recent evidence suggests that resistant starch (RS) is the single most important substrate for bacterial carbohydrate fermentation in the human colon. During two 4-wk periods. 12 healthy volunteers consumed a controlled basal diet enriched with either amylomaize starch (55.2 +/- 3.5 g RS/d; high-RS diet) or available cornstarch (7.7 +/- 0.3 g RS/d; low-RS diet). Approximately 90% of the RS consumed disappeared during intestinal passage; increased fermentation was verified by elevated breath-hydrogen excretion. During the high-RS diet, fecal wet and dry weight increased 49% and 56%, respectively (P < or = 0.005), whereas stool water content did not change significantly. Fecal concentrations and daily excretion of short-chain fatty acids were not different in the two study periods. During the high-RS diet, bacterial beta-glucosidase activity decreased by 26% (P < or = 0.05). Fecal concentrations of total and secondary bile acids were significantly lower during the high-RS than during the low-RS period [a decrease of 30% (P < or = 0.05) and 32% (P < or = 0.01), respectively, in total and secondary bile acids] whereas concentrations of primary bile acids were unaffected by RS consumption. During the high-RS diet, fecal concentrations of total neutral sterols decreased by 30% (P < or = 0.005) and fecal concentrations of 4-cholesten-3-one decreased by 36% (P < or = 0.05). These data suggest that RS has potentially important effects on bacterial metabolism in the human colon that may be relevant for cancer prevention.

The slow digestible disaccharide isomaltulose (iso; Palatinose™) is available as novel functional carbohydrate ingredient for manufacturing of low glycaemic foods and beverages. Although basically characterised, various information on physiological effects of iso are still lacking. Thus, the objective of the present study was to expand scientific knowledge of physiological characteristics of iso by a set of three human intervention trials. Using an ileostomy model, iso was found to be essentially absorbed, irrespective of the nature of food (beverage and solid food). Apparent digestibility of 50 g iso from two different meals was 95·5 and 98·8 %; apparent absorption was 93·6 and 96·1 %, respectively. In healthy volunteers, a single dose intake of iso resulted in lower postprandial blood glucose and insulin responses than did sucrose (suc), while showing prolonged blood glucose delivery over 3 h test. In a 4-week trial with hyperlipidaemic individuals, regular consumption of 50 g/d iso within a Western-type diet was well tolerated and did not affect blood lipids. Fasting blood glucose and insulin resistance were lower after the 4-week iso intervention compared with baseline. This would be consistent with possible beneficial metabolic effects as a consequence of the lower and prolonged glycaemic response and lower insulinaemic burden. However, there was no significant difference at 4 weeks after iso compared with suc. In conclusion, the study shows that iso is completely available from the small intestine, irrespective of food matrix, leading to a prolonged delivery of blood glucose. Regular iso consumption is well tolerated also in subjects with increased risk for vascular diseases.

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Due to its low digestibility in the small intestine, a major fraction of the polyol isomalt reaches the colon. However, little is known about effects on the intestinal microflora. During two 4-week periods in a double-blind, placebo-controlled, cross-over design, nineteen healthy volunteers consumed a controlled basal diet enriched with either 30 g isomalt or 30 g sucrose daily. Stools were collected at the end of each test phase and various microbiological and luminal markers were analysed. Fermentation characteristics of isomalt were also investigated in vitro. Microbiological analyses of faecal samples indicated a shift of the gut flora towards an increase of bifidobacteria following consumption of the isomalt diet compared with the sucrose diet (P, 0·05). During the isomalt phase, the activity of bacterial b-glucosidase decreased (P, 0·05) whereas b-glucuronidase, sulfatase, nitroreductase and urease remained unchanged. Faecal polyamines were not different between test periods with the exception of cadaverine, which showed a trend towards a lower concentration following isomalt (P¼0·055). Faecal SCFA, lactate, bile acids, neutral sterols, N, NH 3 , phenol and p-cresol were not affected by isomalt consumption. In vitro, isomalt was metabolized in several bifidobacteria strains and yielded high butyrate concentrations. Isomalt, which is used widely as a low-glycaemic and low-energy sweetener, has to be considered a prebiotic carbohydrate that might contribute to a healthy luminal environment of the colonic mucosa.

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