The digestibility of ispaghula, a mucilage from Plantago ovata composed mainly of arabinoxylans, and its faecal bulking effect were studied in seven healthy volunteers who ingested a low fibre controiled diet plus either placebo or 18 glday ofispaghula for two 15 day periods. Whole gut transit time and gas excretion in breath and flatus were not different during the periods of ispaghula and placebo ingestion. Faecal wet and dry weights rose significantly, however, during ispaghula ingestion. Faecal short chain fatty acid concentrations and the molar proportions of propionic and acetic acids also increased. Most of the ispaghula had reached the caecum four hours after ingestion in an intact highly polymerised form. During ispaghula ingestion, the increase in the faecal output of neutral sugars was accounted for by the faecal excretion of arabinose and xylose in an intact highly polymerised form; the apparent digestibilities of these sugars were 24 (11) and 53% (6) respectively (mean (SEM)). In conclusion, ispaghula is more resistant to fermentation than previously reported in humans, and its bulking effect largely results from intact material.

Objective: To assess the effects of drug-induced changes in mean transit time (MTT) on the activity of human fecal¯ora in vitro. Methods: The activity of fecal¯ora was estimated by the ability of a fecal inoculum to ferment a substrate (beet ®ber) in vitro in a batch system for 24 h. The inoculum was collected from 8 healthy volunteers studied during three 3-week randomized periods, who received a controlled diet alone (control period) or the same diet with either cisapride or loperamide. Cisapride and loperamide were adjusted in order to halve and double MTT measured during the control period. At the end of each period, the percentage disappearance of the initial added substrate and the concentration and the pro®le of short-chain fatty acids (SCFAs), were determined. Results: In the control period, the pH of the inoculum and SCFA concentration were inversely related to MTT (P 0.0001). Individual SCFA production was also signi®cantly related to MTT (P`0.01). Cisapride-reduced transit time was associated with a signi®cant rise in the concentrations of total SCFAs (P`0.05), propionic and butyric acids (P`0.05) and the percentage substrate disappearance (P`0.05). Inverse relations were observed during the loperamide period. Moreover, MTT was inversely related to the percentage substrate disappearance (P`0.001), SCFA production (P`0.001) and butyrate production (P`0.0005). Conclusion: Changes in MTT alter bacterial activity and modify the bacterial pathways affecting the proportion of individual SCFAs. Sponsorship:

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The physiological effects of dietary fibres in humans are due to their physico-chemical properties. However, it is difficult to predict these effects simply by measuring certain characteristics in vitro. Studies in human subjects are still required to assess the effectiveness of new substrates. The aim of the present study in healthy human subjects was to evaluate the effects of two novel fibres, potato (PF) and maize (MF), on fasting and postprandial blood concentrations of carbohydrate and lipid metabolites as well as on stool ouput and transit time. The chemical composition, water-binding capacity (WBC) and fermentative properties of the fibres were also characterized in order to determine their possible involvement in digestive and metabolic effects. Stools, as well as breath and blood samples, were collected after consumption for 1 month of either a basal diet (control) or a basal diet supplemented with fibre (lSg/d). MF resisted fermentation better than PF and had lower digestibility. However, both fibres increased faecal output of dry matter, neutral sugars and water. There was an inverse relationship between stool weight and orofaecal transit time, although only MF significantly reduced transit time. Orocaecal transit was lengthened by PF, probably because of its high WBC. PF ingestion also decreased postprandial plasma levels of total and esterified cholesterol but had no effect on fasting concentrations. In contrast, MF lowered fasting cholesterolaemia and increased free:esterified cholesterol. These particular physiological and fermentative properties suggest that PF and MF would be suitable ingredients in a healthy diet. Dietary fibre: Stool output: Transit time: Plasma Upids IThe mechanisms by which a particular dietary fibre acts on human physiology are mainly related to its physico-chemical properties. For instance, solubility seems to be particularly involved in the metabolic effects of fibre. Soluble fibres can apparently reduce serum cholesterol concentration, whereas insoluble ones are usually ineffective (Glore et al. 1994). Other properties, such as viscosity and the ability to sequester bile salts, can also influence glucose and cholesterol metabolism (Wolever, 1995). The effects of dietary fibre on digestive functions also depend on several physico-chemical properties of substrates. It is now recognized that fibre can affect stool weight and transit time through two main mechanisms. First, it may act by increasing lumen volume. This mechanism depends on the amount of indigestible residue in the colon, the water-binding capacity (WBC) of the residue, the stimulation of microbial growth, and the production of gas (Cummings, 1986). The resulting increase in stool volume may cause colonic propulsion through excitation of enteric mechanoreceptors, thus decreasing transit time. Second, fibre may act directly on colonic motility either by mechanical stimulation of submucosal neural receptors (Cherbut & Ruckebusch, 1985) or by an effect of fermentation end-products, e.g. short-chain fatty acids (S...