This review aims to investigate the relationship between the health impact of whole grains mediated via the interaction with intestinal microbiota and intestinal barrier function with special interest on tryptophan metabolism, focusing on the role of the intestinal microbiota and their impact on barrier function. Consuming various types of whole grains can lead to the growth of different microbiota species, which in turn leads to the production of diverse metabolites, including those derived from tryptophan metabolism, although the impact of whole grains on intestinal microbiota composition results remains inconclusive and vary among different studies. Whole grains can exert an influence on tryptophan metabolism through interactions with the intestinal microbiota, and the presence of fibre in whole grains plays a notable role in establishing this connection. The impact of whole grains on intestinal barrier function is closely related to their effects on the composition and activity of intestinal microbiota, and SCFA and tryptophan metabolites serve as potential links connecting whole grains, intestinal microbiota and the intestinal barrier function. Tryptophan metabolites affect various aspects of the intestinal barrier, such as immune balance, mucus and microbial barrier, tight junction complexes and the differentiation and proliferation of epithelial cells. Despite the encouraging discoveries in this area of research, the evidence regarding the effects of whole grain consumption on intestine-related activity remains limited. Hence, we can conclude that we are just starting to understand the actual complexity of the intestinal factors mediating in part the health impacts of whole grain cereals.

In recent years, a wealth of factors are associated with increased risk of developing non-alcoholic fatty liver disease (NAFLD) and NAFLD is now thought to increase the risk of multiple extra-hepatic diseases. The aim of this review is first to focus on the role of ageing and sex as key, poorly understood risk factors in the development and progression of NAFLD. Secondly, we aim to discuss the roles of white adipose tissue (WAT) and intestinal dysfunction, as producers of extra-hepatic factors known to further contribute to the pathogenesis of NAFLD. Finally, we aim to summarise the role of NAFLD as a multi-system disease affecting other organ systems beyond the liver. Both increased age and male sex increase the risk of NAFLD and this may be partly driven by alterations in the distribution and function of WAT. Similarly, changes in gut microbiota composition and intestinal function with ageing and chronic overnutrition are likely to contribute to the development of NAFLD both directly (i.e. by affecting hepatic function) and indirectly via exacerbating WAT dysfunction. Consequently, the presence of NAFLD significantly increases the risk of various extra-hepatic diseases including CVD, type 2 diabetes mellitus, chronic kidney disease and certain extra-hepatic cancers. Thus changes in WAT and intestinal function with ageing and chronic overnutrition contribute to the development of NAFLD – a multi-system disease that subsequently contributes to the development of other chronic cardiometabolic diseases.

Lipopolysaccharides (LPS) could induce milk fat depression via regulating the body and blood fat metabolism. However, it is not completely clear how LPS might regulate triglyceride synthesis in dairy cow mammary epithelial cells (DCMECs). DCMECs were isolated and purified from dairy cow mammary tissue and treated with LPS. The level of triglyceride synthesis, the expression and activity of the liver X receptor α (LXRα), enzymes related to de novo fatty acid synthesis, and the expression of the fatty acid transporters were investigated. We found that LPS decreased the level of triglyceride synthesis via a down-regulation of the transcription, translation, and nuclear translocation level of the LXRα. The results also indicated that the transcription level of the LXRα target genes, sterol regulatory element binding protein 1 (SREBP1), fatty acid synthetase (FAS), acetyl-CoA carboxylase-1 (ACC1), were significantly down-regulated in DCMECs after LPS treatment. Our data may provide new insight into the mechanisms of milk fat depression caused by LPS.

Antibiotics rank as the most powerful weapons against bacterial infection, but their use is often limited by antibiotic-associated diarrhoea (AAD). Here, we reported that glutamine deficiency might act as a new link between clindamycin-induced dysbiosis and intestinal barrier dysfunction during AAD progression. Using a mouse model, we demonstrated that glutamine became a conditionally essential amino acid upon persistent therapeutic-dose clindamycin exposure, evidenced by a dramatic decrease in intestinal glutamine level and glutaminase expression. Mechanistically, clindamycin substantially confounded the abundance of butyrate-producing strains, leading to the deficiency of faecal butyrate which is normally a fundamental fuel for enterocytes, and in turn increased the compensatory use of glutamine. In addition to its pivotal roles in colonic epithelial cell turnover, glutamine was required for nitric oxide production in classic macrophage-driven host defence facilitating pathogen removal. Importantly, oral administration of glutamine effectively attenuated clindamycin-induced dysbiosis and restored intestinal barrier dysfunction in mice. Collectively, the present study highlighted the importance of gut microbiota in host energy homoeostasis and provided a rationale for introducing glutamine supplementation to patients receiving long-term antibiotic treatment.

Bile acids (BA) have emerged as signalling molecules regulating intestinal physiology. The importance of intestinal microbiota in production of secondary BA, for example, lithocholic acid (LCA) which impairs enterocyte proliferation and permeability, triggered us to determine the effects of oral probiotics on intestinal BA metabolism. Piglets were weaned at 28 d of age and allocated into control (CON, n 14) or probiotic (PRO, n 14) group fed 50 mg of Lactobacillus plantarum daily, and gut microbiota and BA profile were determined. To test the potential interaction of LCA with bacteria endotoxins in inducing damage of enterocytes, IPEC-J2 cells were treated with LCA, lipopolysaccharide (LPS) and LCA + LPS and expressions of genes related to inflammation, antioxidant capacity and nutrient transport were determined. Compared with the CON group, the PRO group showed lower total LCA level in the ileum and higher relative abundance of the Lactobacillus genus in faeces. In contrast, the relative abundances of Bacteroides, Clostridium_sensu_stricto_1, Parabacteroides and Ruminococcus_1, important bacteria genera in BA biotransformation, were all lower in the PRO than in the CON group. Moreover, PRO piglets had lower postprandial glucagon-like peptide-1 level, while higher glucose level than CON piglets. Co-administration of LPS and LCA led to down-regulated expression of glucose and peptide transporter genes in IPEC-J2 cells. Altogether, oral L. plantarum altered BA profile probably by modulating relative abundances of gut microbial genera that play key roles in BA metabolism and might consequently impact glucose homoeostasis. The detrimental effect of LCA on nutrient transport in enterocytes might be aggravated under LPS challenge.

In this systematic review, we critically evaluated human clinical trials that assessed the effects of dietary fat quality on metabolic endotoxaemia. The studies were selected from three databases (PubMed, Scopus and Cochrane Library), and the keywords were defined according to the Medical Subject Headings indexing terminology. Two authors searched independently, according to the pre-defined selection criteria. Quality and risk assessment of bias for each selected study were also evaluated. The results of the included studies demonstrated associations between higher SFA intake and increased postprandial lipopolysaccharide (LPS) concentrations. On the other hand, after the consumption of PUFA, bloodstream LPS concentrations were lower. However, in none of the long-term studies, the consumption of dietary fats did not seem to exert effects on LPS concentration. Hence, SFA seem to act as a risk factor for transient increase in endotoxaemia, while PUFA demonstrated exerting a protective effect. Taken together, the evidence suggests that the dietary fatty acid profile may influence bloodstream endotoxin concentrations through modulation of factors such LPS clearance, alkaline phosphatase activity, bile acid metabolism, intestinal permeability and intestinal microbiota composition.

Starchy diets can induce hindgut dysbiosis in horses. The present study evaluated the impact of a yeast (Saccharomyces cerevisiae) and microalgae (Aurantiochytrium limacinum) supplementation on caecal, colonic and faecal microbial ecosystem and on blood inflammatory parameters of horses fed high-fibre or high-starch diets. Six fistulated geldings in a 2 × 2 Latin-square design were alternatively supplemented and received during each period 100 % hay (4 weeks) followed by a 56/44 hay/barley diet (3 weeks). Caecal, colonic and faecal samples were collected 4 h after the morning meal three times per diet, at 5-d intervals, to measure bacterial composition and microbial end products. Blood was simultaneously collected for measuring inflammatory markers. The starchy diet clearly modified the microbial ecosystem in the three digestive segments, with an increase of the amylolytic function and a decrease of the fibrolytic one. However, no effect of the diet was observed on the blood parameters. When horses were supplemented, no significant change was found in lipopolysaccharides, PG-E2, serum amyloid A concentrations and complete blood count neither in cellulose-utilising, starch-utilising and lactate-utilising bacteria concentrations nor in the volatile fatty acids and lactate concentrations and pH. Under supplementation, relative abundance of Family XIII Clostridiales increased in caecum and faeces irrespective of diet and relative abundance of Veillonellaceae was higher during the hay/barley diet in colon and faeces. Most variations of faecal bacterial taxa under supplementation were not observed in the hindgut. However, all variations suggested that supplementation could increase fibrolytic function whatever the diet and limit dysbiosis when the horses’ diet changed from high fibre to high starch.

The performance of immune system is vital for defending the body from pathogens, and it plays a crucial role in health homoeostasis. In a previous study, we have shown that LFP-20, a twenty-amino acid antimicrobial peptide in the N terminus of porcine lactoferrin, modulated inflammatory response in colitis. Here, we further investigated the effects of LFP-20 on immune homoeostasis to elucidate the mechanism of its anti-inflammation action. A lipopolysaccharide (LPS)-triggered systemic inflammatory response mice model was established. On the basis of observed mucosal lesions and apoptosis in small intestine, we found increased macrophage and neutrophil infiltration in ileum after LPS stimulation. Expectedly, LFP-20 pre-treatment attenuated the LPS-mediated immune disorders in ileum. Moreover, the flow cytometry results indicated pre-treatment with LFP-20 sustained the balance of CD3+CD8+ T cells, B cells and natural killer cells in LPS-triggered immune disturbance. Simultaneously, we demonstrated LFP-20 modulated the secretion of both activated Th1-related IL-12p70, interferon-γ, TNF-α and Th2-related IL-4, IL-5 and IL-6. Furthermore, we found LFP-20 facilitated a balanced Th1 and Th2 response, which triggered cellular defence mechanisms and induced B cells to produce opsonising antibodies belonging to certain IgG subclasses to defend against LPS stimulation. Collectively, our study indicated pre-treatment with LFP-20 could defend against LPS-triggered systemic inflammatory response in mice via modulating immune homoeostasis.

This review presents mechanistic studies performed in vitro and in animal models, as well as data obtained in patients that contribute to a better understanding of the impact of nutrients interacting with the gut microbiota on metabolic and behavioural alterations linked to obesity. The gut microbiota composition and function are altered in several pathological conditions including obesity and related diseases i.e. non-alcoholic fatty liver diseases (NAFLD). The gut–liver axis is clearly influenced by alterations of the gut barrier that drives inflammation. In addition, recent papers propose that specific metabolites issued from the metabolic cooperation between the gut microbes and host enzymes, modulate inflammation and gene expression in the liver. This review illustrates how dietary intervention with prebiotics or probiotics influences host energy metabolism and inflammation. Indeed, intervention studies are currently underway in obese and NAFLD patients to unravel the relevance of the changes in gut microbiota composition in the management of metabolic and behavioural disorders by nutrients interacting with the gut microbiota. In conclusion, diet is among the main triggers of NAFLD and the gut microbiota is modified accordingly, underlining the importance of the concomitant study of the nutrients and microbial impact on liver health and metabolism, in order to propose innovative, clinically relevant, therapeutic approaches.

Sterol regulatory element binding protein 1 (SREBP1) has a central regulatory effect on milk fat synthesis. Lipopolysaccharides (LPS) can induce mastitis and cause milk fat depression in cows. SREBP1 is also known to be associated with inflammatory regulation. Thus, in the current study, we hypothesized that LPS-induced milk fat depression in dairy cow mammary epithelial cells (DCMECs) operates via decreased SREBP1 expression and activity. To examine the hypothesis, DCMECs were isolated and purified from dairy cow mammary tissue and treated with LPS (10 µg/ml). LPS treatment of DCMECs suppressed lipid-metabolism-related transcription factor SREBP1 mRNA expression, nuclear translocation and protein expression, leading to reduced triglyceride content. The transcription levels of acetyl-CoA carboxylase-1 and fatty acid synthetase were significantly down-regulated in DCMECs after LPS treatment, suggesting that acetyl-CoA carboxylase-1 and fatty acid synthetase involved in de novo milk fat synthesis was regulated by SREBP1. In summary, these results suggest that LPS induces milk fat depression in dairy cow mammary epithelial cells via decreased expression of SREBP1 in a time-dependent manner.

This study was conducted to investigate the protective effects of l-threonine (l-Thr) supplementation on growth performance, inflammatory responses and intestinal barrier function of young broilers challenged with lipopolysaccharide (LPS). A total of 144 1-d-old male chicks were allocated to one of three treatments: non-challenged broilers fed a basal diet (control group), LPS-challenged broilers fed a basal diet without l-Thr supplementation and LPS-challenged broilers fed a basal diet supplemented with 3·0 g/kg l-Thr. LPS challenge was performed intraperitoneally at 17, 19 and 21 d of age, whereas the control group received physiological saline injection. Compared with the control group, LPS challenge impaired growth performance of broilers, and l-Thr administration reversed LPS-induced increase in feed/gain ratio. LPS challenge elevated blood cell counts related to inflammation, and pro-inflammatory cytokine concentrations in serum (IL-1β and TNF-α), spleen (IL-1β and TNF-α) and intestinal mucosa (jejunal interferon-γ (IFN-γ) and ileal IL-1β). The concentrations of intestinal cytokines in LPS-challenged broilers were reduced by l-Thr supplementation. LPS administration increased circulating d-lactic acid concentration, whereas it reduced villus height, the ratio between villus height and crypt depth and goblet density in both jejunum and ileum. LPS-induced decreases in jejunal villus height, intestinal villus height:crypt depth ratio and ileal goblet cell density were reversed with l-Thr supplementation. Similarly, LPS-induced alterations in the intestinal mRNA abundances of genes related to intestinal inflammation and barrier function (jejunal toll-like receptor 4, IFN-γ and claudin-3, and ileal IL-1β and zonula occludens-1) were normalised with l-Thr administration. It can be concluded that l-Thr supplementation could attenuate LPS-induced inflammatory responses and intestinal barrier damage of young broilers.

This study was conducted to evaluate whether medium-chain TAG (MCT) could alleviate Escherichia coli lipopolysaccharide (LPS)-induced intestinal injury by regulating intestinal epithelial inflammatory response, as well as necroptosis. A total of twenty-four weanling piglets were randomly allotted to one of four treatments in a 2×2 factorial arrangement including diet type (5 % maize oil v. 4 % MCT+1 % maize oil) and immune stress (saline v. E. coli LPS). The piglets were fed diets containing maize oil or MCT for 21 d. On 21 d, piglets were injected intraperitoneally with saline or LPS. The blood and intestinal samples were collected at 4 h post injection. Supplementation with MCT improved intestinal morphology, digestive and barrier function, indicated by increased jejunal villus height, increased jejunal and ileal disaccharidases (sucrase and maltase) activities, as well as enhanced protein expression of claudin-1. Furthermore, the protein expression of heat-shock protein 70 in jejunum and the concentration of TNF-α in plasma were reduced in the piglets fed diets supplemented with MCT. In addition, MCT down-regulated the mRNA expression of toll-like receptor 4 (TLR4) and nucleotide-binding oligomerisation domain proteins (NOD) signalling-related genes in jejunum and ileum. Finally, MCT inhibited jejunal and ileal enterocyte necroptosis indicated by suppressed mRNA expression of the receptor-interacting protein 3 and mixed-lineage kinase domain-like protein. These results indicate that MCT supplementation may be closely related to inhibition of TLR4, NOD and necroptosis signalling pathways and concomitant improvement of intestinal integrity under an inflammatory condition.

Polymannuronic acid (PM), one of numerous alginates isolated from brown seaweeds, is known to possess antioxidant activities. In this study, we examined its potential role in reducing body weight gain and attenuating inflammation induced by a high-fat and high-sucrose diet (HFD) as well as its effect on modulating the gut microbiome in mice. A 30-d PM treatment significantly reduced the diet-induced body weight gain and blood TAG levels (P<0·05) and improved glucose tolerance in male C57BL/6J mice. PM decreased lipopolysaccharides in blood and ameliorated local inflammation in the colon and the epididymal adipose tissue. Compared with low-fat and low-sucrose diet (LFD), HFD significantly reduced the mean number of species-level operational taxonomic units (OTU) per sample as well as species richness (P<0·05) but did not appear to affect other microbial diversity indices. Moreover, compared with LFD, HFD altered the abundance of approximately 23 % of the OTU detected (log10 linear discriminant analysis (LDA) score>2·0). PM also had a profound impact on the microbial composition in the gut microbiome and resulted in a distinct microbiome structure. For example, PM significantly increased the abundance of a probiotic bacterium, Lactobacillus reuteri (log10 LDA score>2·0). Together, our results suggest that PM may exert its immunoregulatory effects by enhancing proliferation of several species with probiotic activities while repressing the abundance of the microbial taxa that harbor potential pathogens. Our findings should facilitate mechanistic studies on PM as a potential bioactive compound to alleviate obesity and the metabolic syndrome.

Faeces could be used for evaluating the balance of the equine hindgut microbial ecosystem, which would offer a practical method for assessing gut health and how this relates to disease. However, previous studies concluded that faeces microbial ecosystem was not representative of the proximal hindgut (caecum and ventral colon). This study aimed to evaluate if variations of the faecal microbial ecosystem were similar to those observed in the proximal hindgut. Six horses, fistulated in the caecum and right ventral (RV) colon, were subjected to a gradual change of diet, from a 100% hay (high fibre) diet (2.2 DM kg/day per 100 kg BW) to a 57% hay+43% barley (high starch) diet (0.8 DM kg/day per 100 kg BW hay and 0.6 DM kg/day per 100 kg BW barley). The two diets were iso-energetic and fed over a 3-week trial period. Samples of digesta from the caecum, RV colon and faeces were collected two times on the 10th and 20th day of the trial, for each diet to assess the microbial ecosystem parameters by both classical culture technics and biochemical methods. The variations observed in the caecal and colonic bacterial composition (increase in total anaerobic, amylolytic and lactate-utilizing and decrease in cellulolytic bacteria concentrations) and microbial activity (changes in volatile fatty acids concentrations and increase in lactate concentrations) demonstrated that the hay+barley diet caused changes in the hindgut microbial ecosystem. Similar variations were observed in the faecal microbial ecosystem. Feeding the hay+barley diet resulted in higher concentrations of faecal lipopolysaccharides. The functional bacterial group concentrations (cellulolytics, amylolytics and lactate utilizers) were significantly correlated between caecum and faeces and between colon and faeces. From analyses of the metabolites produced from microbial activity, only valerate concentration in the caecum and the proportion of propionate were significantly correlated with the same parameters in the faeces. Results of the principal component analysis performed between all the caecal/faecal and colonic/faecal parameters revealed that the total anaerobic and cellulolytic bacteria concentrations, as well as valerate, l-lactate and lipopolysaccharide concentrations were strongly correlated with several microbial parameters in the caecum (P<0.027; r>|0.45|) and in the colon (P<0.013; r>|0.50|). This demonstrated that faecal samples and their bacterial analyses could be used to represent caecum and RV colon hindgut microbial ecosystem in terms of variations during a change from a high-fibre to a high-starch diet, and thus could be markers of particular interest to diagnostic proximal hindgut microbial disturbances.

Pro-inflammatory cytokines are critical in mechanisms of muscle atrophy. In addition, asparagine (Asn) is necessary for protein synthesis in mammalian cells. We hypothesised that Asn could attenuate lipopolysaccharide (LPS)-induced muscle atrophy in a piglet model. Piglets were allotted to four treatments (non-challenged control, LPS-challenged control, LPS+0·5 % Asn and LPS+1·0 % Asn). On day 21, the piglets were injected with LPS or saline. At 4 h post injection, piglet blood and muscle samples were collected. Asn increased protein and RNA content in muscles, and decreased mRNA expression of muscle atrophy F-box (MAFbx) and muscle RING finger 1 (MuRF1). However, Asn had no effect on the protein abundance of MAFbx and MuRF1. In addition, Asn decreased muscle AMP-activated protein kinase (AMPK) α phosphorylation, but increased muscle protein kinase B (Akt) and Forkhead Box O (FOXO) 1 phosphorylation. Moreover, Asn decreased the concentrations of TNF-α, cortisol and glucagon in plasma, and TNF-α mRNA expression in muscles. Finally, Asn decreased mRNA abundance of muscle toll-like receptor (TLR) 4 and nucleotide-binding oligomerisation domain protein (NOD) signalling-related genes, and regulated their negative regulators. The beneficial effects of Asn on muscle atrophy may be associated with the following: (1) inhibiting muscle protein degradation via activating Akt and inactivating AMPKα and FOXO1; and (2) decreasing the expression of muscle pro-inflammatory cytokines via inhibiting TLR4 and NOD signalling pathways by modulation of their negative regulators.

Stress induces injury in intestinal barrier function in piglets. Long-chain n-3 PUFA have been shown to exhibit potential immunomodulatory and barrier protective effects in animal models and clinical trials. In addition, corticotropin-releasing hormone (CRH)/CRH receptor (CRHR) signalling pathways play an important role in stress-induced alterations of intestinal barrier function. We hypothesised that fish oil could affect intestinal barrier function and CRH/CRHR signalling pathways. In total, thirty-two weaned pigs were allocated to one of four treatments. The experiment consisted of a 2×2 factorial design, and the main factors included immunological challenge (saline or lipopolysaccharide (LPS)) and diet (5 % maize oil or 5 % fish oil). On d 19 of the trial, piglets were treated with saline or LPS. At 4 h after injection, all pigs were killed, and the mesenteric lymph nodes (MLN), liver, spleen and intestinal samples were collected. Fish oil decreased bacterial translocation incidence and the number of translocated micro-organisms in the MLN. Fish oil increased intestinal claudin-1 protein relative concentration and villus height, as well as improved the intestinal morphology. In addition, fish oil supplementation increased intestinal intraepithelial lymphocyte number and prevented elevations in intestinal mast cell and neutrophil numbers induced by LPS challenge. Moreover, fish oil tended to decrease the mRNA expression of intestinal CRHR1, CRH and glucocorticoid receptors. These results suggest that fish oil supplementation improves intestinal barrier function and inhibits CRH/CRHR1 signalling pathway and mast cell tissue density.

The present study was conducted to investigate the anti-inflammatory effect of vitamin D both in juvenile Jian carp (Cyprinus carpio var. Jian) in vivo and in enterocytes in vitro. In primary enterocytes, exposure to 10 mg lipopolysaccharide (LPS)/l increased lactate dehydrogenase activity in the culture medium (P<0·05) and resulted in a significant loss of cell viability (P<0·05). LPS exposure increased (P<0·05) the mRNA expression of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-8), which was decreased by pre-treatment with 1,25-dihydroxyvitamin D (1,25D3) in a dose-dependent manner (P<0·05). Further results showed that pre-treatment with 1,25D3 down-regulated Toll-like receptor 4 (TLR4), myeloid differentiation primary response gene 88 (Myd88) and NF-κB p65 mRNA expression (P<0·05), suggesting potential mechanisms against LPS-induced inflammatory response. In vivo, intraperitoneal injection of LPS significantly increased TNF-α, IL-1β, IL-6 and IL-8 mRNA expression in the intestine of carp (P<0·05). Pre-treatment of fish with vitamin D3 protected the fish intestine from the LPS-induced increase of TNF-α, IL-1β, IL-6 and IL-8 mainly by downregulating TLR4, Myd88 and NF-κB p65 mRNA expression (P<0·05). These observations suggest that vitamin D could inhibit LPS-induced inflammatory response in juvenile Jian carp in vivo and in enterocytes in vitro. The anti-inflammatory effect of vitamin D is mediated at least in part by TLR4-Myd88 signalling pathways in the intestine and enterocytes of juvenile Jian carp.

The microbial community populating the human digestive tract has been linked to the development of obesity, diabetes and liver diseases. Proposed mechanisms on how the gut microbiota could contribute to obesity and metabolic diseases include: (1) improved energy extraction from diet by the conversion of dietary fibre to SCFA; (2) increased intestinal permeability for bacterial lipopolysaccharides (LPS) in response to the consumption of high-fat diets resulting in an elevated systemic LPS level and low-grade inflammation. Animal studies indicate differences in the physiologic effects of fermentable and non-fermentable dietary fibres as well as differences in long- and short-term effects of fermentable dietary fibre. The human intestinal microbiome is enriched in genes involved in the degradation of indigestible polysaccharides. The extent to which dietary fibres are fermented and in which molar ratio SCFA are formed depends on their physicochemical properties and on the individual microbiome. Acetate and propionate play an important role in lipid and glucose metabolism. Acetate serves as a substrate for de novo lipogenesis in liver, whereas propionate can be utilised for gluconeogenesis. The conversion of fermentable dietary fibre to SCFA provides additional energy to the host which could promote obesity. However, epidemiologic studies indicate that diets rich in fibre rather prevent than promote obesity development. This may be due to the fact that SCFA are also ligands of free fatty acid receptors (FFAR). Activation of FFAR leads to an increased expression and secretion of enteroendocrine hormones such as glucagon-like-peptide 1 or peptide YY which cause satiety. In conclusion, the role of SCFA in host energy balance needs to be re-evaluated.

Lipopolysaccharide (LPS) may play an important role in chronic diseases through the activation of inflammatory responses. The type of diet consumed is of major concern for the prevention and treatment of these diseases. Evidence from animal and human studies has shown that LPS can diffuse from the gut to the circulatory system in response to the intake of high amounts of fat. The method by which LPS move into the circulatory system is either through direct diffusion due to intestinal paracellular permeability or through absorption by enterocytes during chylomicron secretion. Considering the impact of metabolic diseases on public health and the association between these diseases and the levels of LPS in the circulatory system, this review will mainly discuss the current knowledge about high-fat diets and subclinical inflammation. It will also describe the new evidence that correlates gut microbiota, intestinal permeability and alkaline phosphatase activity with increased blood LPS levels and the biological effects of this increase, such as insulin resistance. Although the majority of the studies published so far have assessed the effects of dietary fat, additional studies are necessary to deepen the understanding of how the amount, the quality and the structure of the fat may affect endotoxaemia. The potential of food combinations to reduce the negative effects of fat intake should also be considered in future studies. In these studies, the effects of flavonoids, prebiotics and probiotics on endotoxaemia should be investigated. Thus, it is essential to identify dietetic strategies capable of minimising endotoxaemia and its postprandial inflammatory effects.