Jean Delort-Laval

Sugar composition of dietary fibre and short-chain fatty acid production during in vitro fermentation by human bacteria

The aim of the present study was to assess the relationship between the disappearance of dietary fibre sugars and the production of individual short-chain fatty acids (SCFA). The bacterial degradation of five dietary fibres whose sugars were quantified was investigated in vitro using a human faecal inoculum. Involvement of the main fibre sugars in SCFA production was evaluated by a stepwise multiple linear regression. The results show first that the nature and chiefly the associations between the fibre sugars were key variables in the fermentability. Second, the nature and the amounts of SCFA produced were closely related to the in vitro fermentation of the main sugars available: uronic acids seemed to be principally involved in the production of acetic acid whereas the production of propionic acid could be promoted by the fermentation of glucose and, to a lesser extent, by that of xylose and arabinose. Xylose tended to have a greater impact than uronic acids and glucose on the production of butyric acid. Thus, it would be possible to predict which SCFA could be specifically produced during the fermentation of a fibre, as far as the chemical composition and structure of this fibre are known.

Involvement of small intestinal motility in blood glucose response to dietary fibre in man

Three dietary fibres with different physicochemical properties were studied in healthy humans for their effects on small intestinal motility and postprandial hyperglycaemia. Duodeno-jejunal motor activity was evaluated electromyographically for 180 min in six subjects who had ingested a test meal composed of glucose alone or glucose with 15 g of wheat bran (WB), sugar beet (SB) or ispaghula (I) fibres. Glucose and insulin concentrations were determined during the same period. Each subject received each of the four test meals randomly during a 4 d period. Addition of SB or I to the glucose meal altered duodeno-jejunal motility. Both of these fibres inhibited stationary contractile activity and increased the propagation length and velocity of propagated activity, whereas addition of WB had no effect. These results could reflect the high water-holding capacity of SB and I. Blood glycaemic response to the glucose meal was reduced by SB and I but remained unchanged with WB. Postprandial blood glucose levels were significantly correlated with the total motility index (r 0.82) and stationary activity (r 0.79). Taken together, these observations suggest that the contractile activity induced by dietary fibre in the small intestine probably plays a major role in delayed glucose absorption.

Dietary fibre effects on intestinal transit in man: involvement of their physicochemical and fermentative properties

In order to study the mechanism of the dietary fibre action on the intestinal transit in man, the chemical nature together with the physicochemical and in vitro fermentative properties of five fibres were evaluated and then related to the effects of the latter on the orocaecal transit time (OCTT) and the orofaecal transit time (OFTT) in healthy volunteers. The results showed that the fibre water-binding capacity might be involved in the OCTT and an increase was observed with a fibre-supplemented diet. The fibres, which were capable of decreasing the OFTT, could act by a mechanical effect if they were not fermented in vitro. However, the partly degradable fibres might also change the OFTT via their products of fermentation. A large production of propionic and butyric acids, in particular, could be responsible for the effects of some fibres on the intestinal transit.

Effect of the Nature of Dietary Fibre on Transit Time and Faecal Excretion in the Growing Pig

Abstract When added to a fibre-free diet, polyethylene, a substance not modified in the digestive tract and devoid of water-holding capacity, reduces mean transit time (MTT) in the gut of the growing pig from 101.3 to 88.8 h and increases faecal water excretion from 2 to 43 g day −1 . It does not modify the digestibility of the other components of the diet. However, with the same amount of added wheat bran, more pronounced effects (MTT: 75.7 h; daily faecal water output: 119 g) are observed. The mechanical properties of indigestible material, therefore, only partly explain its effect on transit time and faecal excretion in the pig.

Digestion and Fermentation Pattern of Various Dietary Fiber Sources in the Rat

Abstract Wheat bran, beet pulp, soya bean hulls and copra meal are potential dietary fiber sources which have very different composition. Their total apparent digestibilities in rats have been shown to vary greatly: non-starch glucose digestibility was 20% for soya bean hulls and 63% for beet pulp. Arabinose from lateral chains of the beet pulp pectins was highly digestible whereas arabinans of wheat bran were poorly digestible. Mannans of copra meal were also highly digestible. The present study indicates that endogenous secretions or bacteria induce an underevaluation of the digestibility of minor neutral sugars in the diets. Parts of the neutral sugars from beet pulp (arabinose and galactose) and from copra meal (mannose) disappear from the stomach faster than others. That could indicate digestion of the polysaccharide containing the sugar and/or a quicker transit of this polysaccharide. In the small intestine, digestion or disappearance of the sugars, initiated in the stomach, was accentuated, but xylose and glucose from wheat bran disappeared faster than arabinose. Digestion in the cecum and colon is known to be due to bacteria which proliferate at this level. They produce, from dietary fibers, variable amounts of fermentation products (volatile fatty acids and gas). This production is not correlated to total digestibility of the dietary fiber. Wheat bran is poorly fermentable and is characterized by its fermentation profile, with a high proportion of butyric acid. Digestion of dietary fibers in the stomach and small intestine has been reported by several authors. Its real mechanism — chemical action by secretion or bacterial fermentation of the gut content — has yet to be identified.

Volatile fatty acid production from lupin meal in the caecum of the rat: the role of cell wall polysaccharides and α-galactosides

The seeds of most legume species are known to induce flatus problems in man and animals. These troubles are characteristic of an extensive fermentation process leading to production of gases (H2, CH4, CO2) and short-chain fatty acids. The latter components appear to have important clinical and physiological implications. Their production, in the case of the lupin, can be attributed to α-galactosides or fibres. To dissociate short-chain fatty acid production owing to α-galactosides from that owing to fibres, a fractionation was carried out with lupin meal. Two fractions were prepared: a protein isolate (used in all the diets as a protein source) and lupin fibres. Three semi-synthetic diets containing the lupin meal (containing most of the α-galactosides of the initial seed), the isolated fibres or a mixture of these two materials, were compared in rats accustomed to these experimental diets for 4 weeks. The animals were slaughtered 4, 10 or 24 h after the beginning of their last meal and volatile fatty acids (VFA) were analysed in their caecum. Of the VFA production arising from the ingestion of lupin meals, 50% appears to be derived from non-starchy polysaccharides, and 50% from the α-galactosides.