To evaluate the effects of synbiotic supplementation on insulin resistance and lipid profile in individuals with the metabolic syndrome, we conducted a randomised, double-blind, placebo-controlled pilot study on thirty-eight subjects with the metabolic syndrome; they were supplemented with either synbiotic capsules containing 200 million of seven strains of friendly bacteria plus fructo-oligosaccharide or placebo capsules twice a day for 28 weeks. Both the synbiotic (G1) and the placebo (G2) groups were advised to follow an energy-balanced diet and physical activity recommendations. Parameters related to the metabolic syndrome and insulin resistance were measured every 7 weeks during the course of the study. After 28 weeks of treatment, the levels of fasting blood sugar and insulin resistance improved significantly in the G1 group (P< 0·001). Both the G1 and G2 groups exhibited significant reductions in TAG levels ( − 71·22 v. − 10·47 mg/dl ( − 0·80 v. − 0·12 mmol/l) respectively; P< 0·001) and total cholesterol levels ( − 21·93 v. − 14·2 mg/dl ( − 0·57 v. − 0·37 mmol/l) respectively; P= 0·01), as well as increases in HDL levels (+7·7 v. +0·05 mg/dl (+0·20 v. +>0·01 mmol/l) respectively; P< 0·001). The mean differences observed were greater in the G1 group. No significant changes were observed in LDL levels, waist circumference, BMI, metabolic equivalent of task and energy intake between the groups. The present results indicate that synbiotic supplementation increases the efficacy of diet therapy in the management of the metabolic syndrome and insulin resistance.

Breath analysis is becoming increasingly established as a means of assessing metabolic, biochemical and physiological function in health and disease. The methods available for these analyses exploit a variety of complex physicochemical principles, but are becoming more easily utilised in the clinical setting. Whilst some of the factors accounting for the biological variation in breath metabolite concentrations have been clarified, there has been relatively little work on the dietary factors that may influence them. In applying breath analysis to the clinical setting, it will be important to consider how these factors may affect the interpretation of endogenous breath composition. Diet may have complex effects on the generation of breath compounds. These effects may either be due to a direct impact on metabolism, or because they alter the gastrointestinal flora. Bacteria are a major source of compounds in breath, and their generation of H2, hydrogen cyanide, aldehydes and alkanes may be an indicator of the health of their host.

Lactoferrin has antimicrobial activity associated with peptide fragments lactoferricin (LFC) and lactoferrampin (LFA) released on digestion. These two fragments have been expressed in Photorhabdus luminescens as a fusion peptide linked to protein cipB. The construct cipB–LFC–LFA was tested as an alternative to antimicrobial growth promoters in pig production. Sixty piglets with an average live body weight of 5·42 (sem 0·59) kg were challenged with enterotoxigenic Escherichia coli and randomly assigned to four treatment groups fed a maize–soyabean meal diet containing either no addition (C), cipB at 100 mg/kg (C+B), cipB–LFC–LFA at 100 mg/kg (C+L) or colistin sulfate at 100 mg/kg (C+CS) for 3 weeks. Compared with C, dietary supplementation with C+L for 3 weeks increased daily weight gain by 21 %, increased recovery from diarrhoea, enhanced serum glutathione peroxidase (GPx), peroxidase (POD) and total antioxidant content (T-AOC), liver GPx, POD, superoxide dismutase and T-AOC, Fe, total Fe-binding capacity, IgA, IgG and IgM levels (P < 0·05), decreased the concentration of E. coli in the ileum, caecum and colon (P < 0·05), increased the concentration of lactobacilli and bifidobacteria in the ileum, caecum and colon (P < 0·05), and promoted development of the villus–crypt architecture of the small intestine. Growth performance was similar between C+L- and C+CS-supplemented pigs. The present results indicate that LFC–LFA is an effective alternative to the feed antibiotic CS for enhancing growth performance in piglets weaned at age 21 d.

Prebiotics are non-digestible (by the host) food ingredients that have a beneficial effect through their selective metabolism in the intestinal tract. Key to this is the specificity of microbial changes. The present paper reviews the concept in terms of three criteria: (a) resistance to gastric acidity, hydrolysis by mammalian enzymes and gastrointestinal absorption; (b) fermentation by intestinal microflora; (c) selective stimulation of the growth and/or activity of intestinal bacteria associated with health and wellbeing. The conclusion is that prebiotics that currently fulfil these three criteria are fructo-oligosaccharides, galacto-oligosaccharides and lactulose, although promise does exist with several other dietary carbohydrates. Given the range of food vehicles that may be fortified by prebiotics, their ability to confer positive microflora changes and the health aspects that may accrue, it is important that robust technologies to assay functionality are used. This would include a molecular-based approach to determine flora changes. The future use of prebiotics may allow species-level changes in the microbiota, an extrapolation into genera other than the bifidobacteria and lactobacilli, and allow preferential use in disease-prone areas of the body.

In the search for alternatives to banned in-feed antibiotics, a concept was developed based on studies with medium-chain fatty acid-containing triacylglycerols (MCTAG) and selected lipases for in situ generation of diacylglycerols, monoacylglycerols and medium-chain fatty acids (MCFA) in the stomach and proximal gut of piglets. MCFA are known to have strong antibacterial properties but can hardly be used as such because of their repellent odour and taste. Those problems could be overcome by the generation of MCFA in situ. The concept was tested in vitro and validated in vivo with gastric-cannulated piglets and under field conditions, including effects on zootechnical performance, with classical antibacterial growth promoters or organic acids acting as positive controls. Furthermore, the metabolic and dietary constraints on the nutritional and nutritive use of MCTAG and/or MCFA (for example, the effects on digestive physiology, gut flora, feed intake, performance, carcass composition) are reviewed. The role of natural preduodenal lipase activity, the presence of endogenous plant lipase activity in raw materials and the feasibility for exogenous lipase addition to the feed are discussed, in order to optimize the concept. The present review illustrates the similarity of the action of MCFA and commonly used antimicrobials on the flora (total flora, Gram-positive flora, Gram-negative flora, potential pathogens) and epithelial morphology and histology in the foregut. These observations are believed to be the basis for obtaining optimal growth performances. In addition, these naturally occurring antimicrobial agents have little or no human or animal toxicity and induce no problems of residues and cross-resistance induction. They are proposed as a valuable alternative to in-feed antibiotics, used for growth promotion, and even for the preventive and curative treatment of gastrointestinal diseases.

A large and diverse variety of bacteria have evolved and adapted to live in the human intestinal habitat in a symbiotic arrangement that influences both physiology and pathology in the host. Symbiosis between host and flora can be optimised by prebiotics. Inulin-type fructans have been shown to improve the metabolic functions of the commensal flora. Clinical and experimental data suggest that they also improve the gut mucosal barrier. Furthermore, modulation of the trophic functions of the flora by these prebiotics could help in the prevention of inflammatory bowel diseases. The anti-inflammatory effects of inulin or oligofructose have been assessed in the rat model of distal colitis induced by dextran sodium sulphate, which histologically resembles human ulcerative colitis, and in the trinitrobenzene sulphonic acid model that resembles human Crohn's disease. Both inulin and oligofructose stimulate colonic production of SCFA and favour the growth of indigenous lactobacilli and/or bifidobacteria. These effects are associated with reduced mucosal inflammation and decreased mucosal lesion scores. Inulin has also been tested in a placebo-controlled clinical trial in patients with relapsing pouchitis. Treatment reduced endoscopic and histological parameters of inflammation of the pouch mucosa. Inulin and oligofructose may offer an opportunity to prevent chronic inflammatory intestinal disorders, and this potential should be tested in further clinical studies.

Probiotic ingestion can be recommended as a preventative approach to maintaining the balance of the intestinal microflora and thereby enhance ‘well-being’. Research into the use of probiotic intervention in specific illnesses and disorders has identified certain patient populations that may benefit from the approach. Undoubtedly, probiotics will vary in their efficacy and it may not be the case that the same results occur with all species. Those that prove most efficient will likely be strains that are robust enough to survive the harsh physico-chemical conditions present in the gastrointestinal tract. This includes gastric acid, bile secretions and competition with the resident microflora. A survey of the literature indicates positive results in over fifty human trials, with prevention/treatment of infections the most frequently reported output. In theory, increased levels of probiotics may induce a ‘barrier’ influence against common pathogens. Mechanisms of effect are likely to include the excretion of acids (lactate, acetate), competition for nutrients and gut receptor sites, immunomodulation and the formation of specific antimicrobial agents. As such, persons susceptible to diarrhoeal infections may benefit greatly from probiotic intake. On a more chronic basis, it has been suggested that some probiotics can help maintain remission in the inflammatory conditions, ulcerative colitis and pouchitis. They have also been suggested to repress enzymes responsible for genotoxin formation. Moreover, studies have suggested that probiotics are as effective as anti-spasmodic drugs in the alleviation of irritable bowel syndrome. The approach of modulating the gut flora for improved health has much relevance for the management of those with acute and chronic gut disorders. Other target groups could include those susceptible to nosocomial infections, as well as the elderly, who have an altered microflora, with a decreased number of beneficial microbial species. For the future, it is imperative that mechanistic interactions involved in probiotic supplementation be identified. Moreover, the survival issues associated with their establishment in the competitive gut ecosytem should be addressed. Here, the use of prebiotics in association with useful probiotics may be a worthwhile approach. A prebiotic is a dietary carbohydrate selectively metabolised by probiotics. Combinations of probiotics and prebiotics are known as synbiotics.

Increasingly, the microbiological scientific community is relying on molecular biology to define the complexity of the gut flora and to distinguish one organism from the next. This is particularly pertinent in the field of probiotics, and probiotic therapy, where identifying probiotics from the commensal flora is often warranted. Current techniques, including genetic fingerprinting, gene sequencing, oligonucleotide probes and specific primer selection, discriminate closely related bacteria with varying degrees of success. Additional molecular methods being employed to determine the constituents of complex microbiota in this area of research are community analysis, denaturing gradient gel electrophoresis (DGGE)/temperature gradient gel electrophoresis (TGGE), fluorescent in situ hybridisation (FISH) and probe grids. Certain approaches enable specific aetiological agents to be monitored, whereas others allow the effects of dietary intervention on bacterial populations to be studied. Other approaches demonstrate diversity, but may not always enable quantification of the population. At the heart of current molecular methods is sequence information gathered from culturable organisms. However, the diversity and novelty identified when applying these methods to the gut microflora demonstrates how little is known about this ecosystem. Of greater concern is the inherent bias associated with some molecular methods. As we understand more of the complexity and dynamics of this diverse microbiota we will be in a position to develop more robust molecular-based technologies to examine it. In addition to identification of the microbiota and discrimination of probiotic strains from commensal organisms, the future of molecular biology in the field of probiotics and the gut flora will, no doubt, stretch to investigations of functionality and activity of the microflora, and/or specific fractions. The quest will be to demonstrate the roles of probiotic strains in vivo and not simply their presence or absence.

The gut of preterm neonates is colonised with a paucity of bacterial species originating more from the environment than from the mother. Furthermore, a delayed colonisation by bifidobacteria promotes colonisation by potentially pathogenic bacteria. This may contribute towards the development of neonatal necrotising enterocolitis (NEC). The physiopathology of NEC is still unclear but immaturity of the gut, enteral feeding and bacterial colonisation are all thought to be involved. None of the current preventive treatments are considered satisfactory. Modulating the autochthonous microflora by probiotics or prebiotics could be a more reliable approach to prevention. Using gnotobiotic quails as an experimental model of NEC we have shown that onset of intestinal lesions requires a combination of low endogenous lactase activity, lactose in diet, and colonisation by lactose-fermenting bacteria such as the clostridia. The protective role of bifidobacteria was demonstrated in this model through a decrease in clostridial populations and in butyric acid. Oligofructose dietary supplementation was shown to enhance this effect with an increase in the bifidobacterial level and consequently a greater decrease in clostridia. However, oligofructose was unable to promote a bifidobacterial acquisition when the microflora was initially deprived of this group. Nevertheless, oligofructose can act as an anti-infective agent and decrease the occurrence or severity of the lesions depending on the bacteria involved. According to these results and to the fact that oligosaccharides are a major component of breast milk, the addition of oligofructose in formula milks may be a nutritional approach to favouring colonisation by a beneficial flora.

The main role of diet is to provide enough nutrients to meet the requirements of a balanced diet, while giving the consumer a feeling of satisfaction and well-being. The most recent knowledge in bioscience supports the hypothesis that diet also controls and modulates various functions in the body, and, in doing so, contributes to the state of good health necessary to reduce the risk of some diseases. It is such an hypothesis which is at the origin both of the concept of ‘functional food’ and the development of a new scientific discipline of ‘functional food science’. In the context of this paper the potential ‘functional foods’ to be discussed are the prebiotics and the synbiotics. The prebiotics developed so far are the non-digestible oligosaccharides and especially the non-digestible fructans among which chicory fructans play a major role. The chicory fructans are β (2-1) fructo-oligosaccharides classified as natural food ingredients. They positively affect various physiological functions in such a way that they are already or may, in the future, be classified as functional food ingredients for which claims of functional effects or of disease risk reduction might become authorized. They are classified as prebiotic and have been shown to induce an increase in the number of bifidobacteria in human faecal flora. As part of a synbiotic-type product, they are already bifidogenic at a dose of 2·75 g/d and the effect lasts for at least 7 weeks. The other potential functional effects are on the bioavailability of minerals, but also, and more systemically, on the metabolism of lipids. Potential health benefits may concern reduction of the risk of intestinal infectious diseases, cardiovascular disease, non-insulin-dependent diabetes, obesity, osteoporosis and cancer. However, except for the prebiotic effect, and tentatively the improvement of calcium bioavailability, the evidence to support such effects is still missing in humans though hypotheses already exist to justify nutrition studies.

The human colonic flora has both beneficial and pathogenic potentials with respect to host health. There is now much interest in manipulation of the microbiota composition in order to improve the potentially beneficial aspects. The prebiotic approach dictates that non-viable food components are specifically fermented in the colon by indigenous bacteria thought to be of positive value, e.g. bifidobacteria, lactobacilli. Any food ingredient that enters the large intestine is a candidate prebiotic. However, to be effective, selectivity of the fermentation is essential. Most current attention and success has been derived using non-digestible oligosaccharides. Types primarily being looked at include those which contain fructose, xylose, soya, galactose, glucose and mannose. In particular, fructose-containing oligosaccharides, which occur naturally in a variety of plants such as onion, asparagus, chicory, banana and artichoke, fulfil the prebiotic criteria. Various data have shown that fructo-oligosaccharides (FOS) are specifically fermented by bifidobacteria. During controlled feeding studies, ingestion of these prebiotics causes bifidobacteria to become numerically dominant in faeces. Recent studies have indicated that a FOS dose of 4g/d is prebiotic. To exploit this concept more fully, there is a need for assessments of (a) improved determination of the gut microbiota composition and activity; (b) the use of molecular methodologies to assess accurately prebiotic identities and develop efficient bacterial probing strategies; (c) the prebiotic potential of raw and processed foods; and (d) the health consequences of dietary modulation.