ObjectiveThe colonic microbiota ferment dietary fibres, producing short chain fatty acids. Recent evidence suggests that the short chain fatty acid propionate may play an important role in appetite regulation. We hypothesised that colonic delivery of propionate would increase peptide YY (PYY) and glucagon like peptide-1 (GLP-1) secretion in humans, and reduce energy intake and weight gain in overweight adults.DesignTo investigate whether propionate promotes PYY and GLP-1 secretion, a primary cultured human colonic cell model was developed. To deliver propionate specifically to the colon, we developed a novel inulin-propionate ester. An acute randomised, controlled cross-over study was used to assess the effects of this inulin-propionate ester on energy intake and plasma PYY and GLP-1 concentrations. The long-term effects of inulin-propionate ester on weight gain were subsequently assessed in a randomised, controlled 24-week study involving 60 overweight adults.ResultsPropionate significantly stimulated the release of PYY and GLP-1 from human colonic cells. Acute ingestion of 10 g inulin-propionate ester significantly increased postprandial plasma PYY and GLP-1 and reduced energy intake. Over 24 weeks, 10 g/day inulin-propionate ester supplementation significantly reduced weight gain, intra-abdominal adipose tissue distribution, intrahepatocellular lipid content and prevented the deterioration in insulin sensitivity observed in the inulin-control group.ConclusionsThese data demonstrate for the first time that increasing colonic propionate prevents weight gain in overweight adult humans.Trial registration numberNCT00750438.

Consumption of anthocyanins has been related with beneficial health effects. However, bioavailability studies have shown low concentration of anthocyanins in plasma and urine. In this study, we have investigated the bacterial-dependent metabolism of malvidin-3-glucoside, gallic acid and a mixture of anthocyanins using a pH-controlled, stirred, batch-culture fermentation system reflective of the distal human large intestine conditions. Most anthocyanins have disappeared after 5 h incubation while gallic acid remained constant through the first 5 h and was almost completely degraded following 24 h of fermentation. Incubation of malvidin-3-glucoside with fecal bacteria mainly resulted in the formation of syringic acid, while the mixture of anthocyanins resulted in formation of gallic, syringic and p-coumaric acids. All the anthocyanins tested enhanced significantly the growth of Bif idobacterium spp. and Lactobacillus−Enterococcus spp. These results suggest that anthocyanins and their metabolites may exert a positive modulation of the intestinal bacterial population.

Short-chain fructooligosaccharides (scFOS) and other prebiotics are used to selectively stimulate the growth and activity of lactobacilli and bifidobacteria in the colon. However, there is little information on the mechanisms whereby prebiotics exert their specific effects upon such microorganisms. To study the genomic basis of scFOS metabolism in Lactobacillus plantarum WCFS1, two-color microarrays were used to screen for differentially expressed genes when grown on scFOS compared to glucose (control). A significant up-regulation (8-to 60-fold) was observed with a set of only five genes located in a single locus and predicted to encode a sucrose phosphoenolpyruvate transport system (PTS), a ␤-fructofuranosidase, a fructokinase, an ␣-glucosidase, and a sucrose operon repressor. Several other genes were slightly overexpressed, including pyruvate dehydrogenase. For the latter, no detectable activity in L. plantarum under various growth conditions has been previously reported. A mannose-PTS likely to encode glucose uptake was 50-fold down-regulated as well as, to a lower extent, other PTSs. Chemical analysis of the different moieties of scFOS that were depleted in the growth medium revealed that the trisaccharide 1-kestose present in scFOS was preferentially utilized, in comparison with the tetrasaccharide nystose and the pentasaccharide fructofuranosylnystose. The main end products of scFOS fermentation were lactate and acetate. This is the first example in lactobacilli of the association of a sucrose PTS and a ␤-fructofuranosidase that could be used for scFOS degradation.Prebiotics are defined as nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon that can improve host health (19). Main targets for the prebiotic approach are bifidobacteria and lactobacilli, as these intestinal bacteria show several positive effects upon human well-being (18,35).Fructooligosaccharides are among the most extensively studied prebiotics and include a diverse family of fructose polymers which vary in length and can either be derivatives of simple fructose polymers or fructose moieties attached to a sucrose molecule. Most fructooligosaccharides marketed as ingredients for foods and nutritional supplements are either synthesized from sucrose using fructosyltransferases derived from Aspergillus niger (short chain fructooligosaccharides [scFOS]) or extracted from chicory roots (Cichoricum intybus) by a partial enzymatic hydrolysis of inulin (FOS). Their general structure can be represented by GF n or F n , in which G and F are, respectively, a glucose or fructose unit and n is the number of fructosyl units. The different units are linked by ␤(231) bonds. The structures of these two sugar classes are similar. FOS and scFOS are resistant to digestion in the stomach and small intestine (3, 15) and thus are able to reach the colon, where they are selectively fermented by beneficial bacteria (7,26).While some limited insight h...

Manipulation of saccharolytic fermentation by prebiotic substrates is beginning to provide information on structure-function relationships relating to the production of SCFAs, which have multiple roles in host homeostasis.

Prebiotics are non-digestible food ingredients that target selected groups of the human colonic microflora, thus having the ability to alter the composition towards a more 'beneficial' community, i.e. selectively increasing populations of bifidobacteria and/or lactobacilli. In the present study the prebiotic potential of partially hydrolysed guar gum (PHGG) and fructooligosaccharides (FOS) in a biscuit was assessed in human volunteers. Fluorescent in situ hybridization using oligonucleotide probes targeting Bacteroides spp., Bifidobacterium spp., Clostridium spp. and Lactobacillus -Enterococcus spp. were used for the bacteriology and total bacteria were enumerated using the fluorescent stain 4 0 ,6-diamidino-2-phenylindole. Thirty-one volunteers consumed daily either three experimental biscuits (providing a total (g/d) of 6 : 6 FOS and 3 : 4 PHGG) or three placebo biscuits for two 21-d crossover periods. Bifidobacteria significantly increased in number on ingestion of the experimental biscuits compared with pretreatment and placebo population levels. Bifidobacterial numbers returned to pretreatment levels within 7 d of the cessation of intake of experimental biscuits. A correlation was observed between the initial faecal bifidobacterial numbers and the magnitude of bifidogenesis, with volunteers who possessed low initial population levels of bifidobacteria experiencing the greatest increase in bifidogenesis. No changes were observed in the other bacterial groups monitored during the trial. Thus, the prebiotic nature of FOS and PHGG was maintained in a final food product as evidenced from the selective increase in bifidobacterial numbers. Gut microflora: Prebiotic: Gene probesThe importance of the human colon in health and disease has become increasingly recognized with a greater understanding of the ecology and biological importance of the human gastrointestinal microflora. More than 500 different bacterial species are thought to make up the gut microbiota, with the total number of bacterial cells present in the colon far exceeding the total number of eukaryotic cells in the body (Conway, 1995;Gibson & Beaumont, 1996; Tannock, 1999). Although it is known that many disease states involve bacterial metabolism, the human gut microflora may also be considered as very relevant to improved host health (Gibson & Beaumont, 1996). For instance, bifidobacteria and lactobacilli are thought to improve resistance to gut infections by inhibiting the growth of harmful bacteria, to reduce cholesterol levels, to improve the immune response and to produce vitamins (Gibson, 1998;Holzapfel et al. 1998;Vanderhoof & Young, 1998;Ziemer & Gibson, 1998). In the present study the efficacy of biscuits containing fructo-oligosaccharides (FOS) and partially hydrolysed guar gum (PHGG) in bringing about a beneficial modulation of the gastrointestinal microflora was determined. Particularly, the ability of the prebiotic biscuits to increase numbers of bifidobacteria selectively was assessed.The complexity of the gut microflora presents diffic...