The different compartments of the gastrointestinal tract are inhabited by populations of micro-organisms. By far the most important predominant populations are in the colon where a true symbiosis with the host exists that is a key for well-being and health. For such a microbiota, ‘normobiosis’ characterises a composition of the gut ‘ecosystem’ in which micro-organisms with potential health benefits predominate in number over potentially harmful ones, in contrast to ‘dysbiosis’, in which one or a few potentially harmful micro-organisms are dominant, thus creating a disease-prone situation. The present document has been written by a group of both academic and industry experts (in the ILSI Europe Prebiotic Expert Group and Prebiotic Task Force, respectively). It does not aim to propose a new definition of a prebiotic nor to identify which food products are classified as prebiotic but rather to validate and expand the original idea of the prebiotic concept (that can be translated in ‘prebiotic effects’), defined as: ‘The selective stimulation of growth and/or activity(ies) of one or a limited number of microbial genus(era)/species in the gut microbiota that confer(s) health benefits to the host.’ Thanks to the methodological and fundamental research of microbiologists, immense progress has very recently been made in our understanding of the gut microbiota. A large number of human intervention studies have been performed that have demonstrated that dietary consumption of certain food products can result in statistically significant changes in the composition of the gut microbiota in line with the prebiotic concept. Thus the prebiotic effect is now a well-established scientific fact. The more data are accumulating, the more it will be recognised that such changes in the microbiota's composition, especially increase in bifidobacteria, can be regarded as a marker of intestinal health. The review is divided in chapters that cover the major areas of nutrition research where a prebiotic effect has tentatively been investigated for potential health benefits. The prebiotic effect has been shown to associate with modulation of biomarkers and activity(ies) of the immune system. Confirming the studies in adults, it has been demonstrated that, in infant nutrition, the prebiotic effect includes a significant change of gut microbiota composition, especially an increase of faecal concentrations of bifidobacteria. This concomitantly improves stool quality (pH, SCFA, frequency and consistency), reduces the risk of gastroenteritis and infections, improves general well-being and reduces the incidence of allergic symptoms such as atopic eczema. Changes in the gut microbiota composition are classically considered as one of the many factors involved in the pathogenesis of either inflammatory bowel disease or irritable bowel syndrome. The use of particular food products with a prebiotic effect has thus been tested in clinical trials with the objective to improve the clinical activity and well-being of patients with such disorders. Promising beneficial effects have been demonstrated in some preliminary studies, including changes in gut microbiota composition (especially increase in bifidobacteria concentration). Often associated with toxic load and/or miscellaneous risk factors, colon cancer is another pathology for which a possible role of gut microbiota composition has been hypothesised. Numerous experimental studies have reported reduction in incidence of tumours and cancers after feeding specific food products with a prebiotic effect. Some of these studies (including one human trial) have also reported that, in such conditions, gut microbiota composition was modified (especially due to increased concentration of bifidobacteria). Dietary intake of particular food products with a prebiotic effect has been shown, especially in adolescents, but also tentatively in postmenopausal women, to increase Ca absorption as well as bone Ca accretion and bone mineral density. Recent data, both from experimental models and from human studies, support the beneficial effects of particular food products with prebiotic properties on energy homaeostasis, satiety regulation and body weight gain. Together, with data in obese animals and patients, these studies support the hypothesis that gut microbiota composition (especially the number of bifidobacteria) may contribute to modulate metabolic processes associated with syndrome X, especially obesity and diabetes type 2. It is plausible, even though not exclusive, that these effects are linked to the microbiota-induced changes and it is feasible to conclude that their mechanisms fit into the prebiotic effect. However, the role of such changes in these health benefits remains to be definitively proven. As a result of the research activity that followed the publication of the prebiotic concept 15 years ago, it has become clear that products that cause a selective modification in the gut microbiota's composition and/or activity(ies) and thus strengthens normobiosis could either induce beneficial physiological effects in the colon and also in extra-intestinal compartments or contribute towards reducing the risk of dysbiosis and associated intestinal and systemic pathologies.

Probiotic bacteria are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. There is a growing interest in probiotics within the scientific community, with consumers, and in the food industry. The interactions between the gut and intestinal microbiota and between resident and transient microbiota define a new arena in physiology, an understanding of which would shed light on the "cross-talk" between humans and microbes. The different beneficial effects of specific probiotic strains may be translated into different health claims. However, there is a need for comprehensive and harmonized guidelines on the assessment of the characteristics and efficacy of probiotics and of foods containing them. An international expert group of ILSI has evaluated the published evidence of the functionality of different probiotics in 4 areas of (human) application: 1) metabolism, 2) chronic intestinal inflammatory and functional disorders, 3) infections, and 4) allergy. Based on the existing evidence, concrete examples of demonstration of benefits and gaps are listed, and guidelines and recommendations are defined that should help design the next generation of probiotic studies.

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Exposure to ultraviolet light, especially UVB wavelengths, can impair immune responses in animals and humans. It is remarkable that this immunomodulation is not restricted to the exposed skin but is also found at other sites, i.e. systemic (distant) immunosuppression. A frequently proposed hypothesis is that UVB exposure inhibits, specifically, T helper 1 (Th1)-mediated immune responses. The major reason for this is that contact hypersensitivity (CHS) and delayed-type hypersensitivity (DTH), both Th1-mediated immune responses, are very sensitive to UVB. For this reason these models are frequently used for photoimmunology studies. In the present study, the effects of UVB exposure were investigated in classical models for Th1-mediated immunity, i.e. CHS models in which picrylchloride or oxazolone were used as low-molecular-weight chemical antigens. In these models, CHS responsiveness and cytokines were measured, the latter by both reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). The CHS responses to both contact sensitizers (picrylchloride and oxazolone) were suppressed significantly by pre-exposure to repeated suberythemal UVB exposure. Interferon-gamma (IFN-gamma), interleukin (IL)-12 and IL-4, but not IL-10, were detectable in spleen and draining lymph nodes of sensitized BALB/c mice. Repeated UVB exposure prior to sensitization at a distant locus inhibited both IFN-gamma and IL-12 but not IL-4. In BALB/c mice sensitized with ovalbumin (OVA) in the absence of complete Freund's adjuvant, a model for Th2-mediated immunity, OVA-specific serum IgE and cytokine profiles in the spleen were analysed. Sensitization did lead to a significant increase in OVA-specific IgE serum titres. Pre-exposure to UVB resulted in a decreased OVA-specific IgE serum titre. Both RT-PCR and ELISA showed increased levels of IFN-gamma, IL-4 and IL-10 in the spleens of OVA-sensitized mice. The production of IFN-gamma and IL-4 was not affected by UVB pre-exposure. In contrast, the production of IL-10 was significantly increased. This was probably caused by an up-regulation of Th2 cells. It is remarkable that IFN-gamma is significantly suppressed by UVB in Th1-mediated immune reactions but not in Th2-mediated immune reactions where it even appears to increase. IL-10, which is up-regulated by UVB pre-exposure and produced by, among others, Th2 cells, may represent a shift from Th1- to Th2-mediated immune mechanisms. However, IL-10 can also inhibit Th2 responses, which might be the reason for a decreased IgE titre in the Th2 model. From the results of this study it is concluded that UVB exposure prior to sensitization/immunization not only inhibits Th1-mediated but also Th2-mediated immune responses.

BackgroundResilience or the ability of our body to cope with daily-life challenges has been proposed as a new definition of health, with restoration of homeostasis as target resultant of various physiological stress responses. Challenge models may thus be a sensitive measure to study the body’s health. The objective of this study was to select a dietary challenge model for the assessment of inflammatory resilience. Meals are a challenge to metabolic homeostasis and are suggested to affect inflammatory pathways, yet data in literature are limited and inconsistent.MethodThe kinetic responses of three different dietary challenges and a water control challenge were assessed on various metabolic and inflammatory markers in 14 healthy males and females using a full cross-over study design. The dietary challenges included glucose (75 g glucose in 300 ml water), lipids (200 ml whipping cream) and a mix of glucose and lipids (same amounts as above), respectively. Blood samples were collected at baseline and at 0.5, 1, 2, 4, 6, 8 and 10 h after consumption of the treatment products. Inflammation (IFNγ, IL-1β, IL-6, IL-8, IL-10, IL-12p70, TNF-α CRP, ICAM-1, VCAM-1, SAA, E-selectin, P-selectin, thrombomodulin, leukocytes, neutrophils, lymphocytes) and clinical (e.g. glucose, insulin, triglycerides) markers as well as gene expression in blood cells and plasma oxylipin profiles were measured.ResultsAll three dietary challenges induced changes related to metabolic control such as increases in glucose and insulin after the glucose challenge and increases in triglycerides after the lipid challenge. In addition, differences between the challenges were observed for precursor oxylipins and some downstream metabolites including DiHETrE’s and HODE’s. However, none of the dietary challenges induced an acute inflammatory response, except for a modest increase in circulating leukocyte numbers after the glucose and mix challenges. Furthermore, subtle, yet statistically significant increases in vascular inflammatory markers (sICAM-1 and sVCAM-1) were found after the mix challenge, when compared to the water control challenge.ConclusionsThis study shows that dietary glucose and lipid challenges did not induce a strong acute inflammatory response in healthy subjects, as quantified by an accurate and broad panel of parameters.