Gut microbiota as a driver of the interindividual variability of cardiometabolic effects from tea polyphenols.

Tea polyphenols have been extensively studied for their preventive properties against cardiometabolic diseases. Nevertheless, the evidence of these effects from human intervention studies is not always consistent, mainly because of a large interindividual variability. The bioavailability of tea polyphenols is low, and metabolism of tea polyphenols highly depends on individual gut microbiota. The accompanying reciprocal relationship between tea polyphenols and gut microbiota may result in alterations in the cardiometabolic effects, however, the underlying mechanism of which is little explored. This review summarizes tea polyphenols-microbiota interaction and its contribution to interindividual variability in cardiometabolic effects. Currently, only a few bacteria that can biodegrade tea polyphenols have been identified and generated metabolites and their bioactivities in metabolic pathways are not fully elucidated. A deeper understanding of the role of complex interaction necessitates fully individualized data, the ntegration of multiple-omics platforms and development of polyphenol-centered databases. Knowledge of this microbial contribution will enable the functional stratification of individuals in the gut microbiota profile (metabotypes) to clarify interindividual variability in the health effects of tea polyphenols. This could be used to predict individual responses to tea polyphenols consumption, hence bringing us closer to personalized nutrition with optimal dose and additional supplementation of specific microorganisms.

Lentils and Yeast Fibers: A New Strategy to Mitigate Enterotoxigenic Escherichia coli (ETEC) Strain H10407 Virulence?

Dietary fibers exhibit well-known beneficial effects on human health, but their anti-infectious properties against enteric pathogens have been poorly investigated. Enterotoxigenic Escherichia coli (ETEC) is a major food-borne pathogen that causes acute traveler's diarrhea. Its virulence traits mainly rely on adhesion to an epithelial surface, mucus degradation, and the secretion of two enterotoxins associated with intestinal inflammation. With the increasing burden of antibiotic resistance worldwide, there is an imperious need to develop novel alternative strategies to control ETEC infections. This study aimed to investigate, using complementary in vitro approaches, the inhibitory potential of two dietary-fiber-containing products (a lentil extract and yeast cell walls) against the human ETEC reference strain H10407. We showed that the lentil extract decreased toxin production in a dose-dependent manner, reduced pro-inflammatory interleukin-8 production, and modulated mucus-related gene induction in ETEC-infected mucus-secreting intestinal cells. We also report that the yeast product reduced ETEC adhesion to mucin and Caco-2/HT29-MTX cells. Both fiber-containing products strengthened intestinal barrier function and modulated toxin-related gene expression. In a complex human gut microbial background, both products did not elicit a significant effect on ETEC colonization. These pioneering data demonstrate the promising role of dietary fibers in controlling different stages of the ETEC infection process.

Ultra-high Pressure Treatment Controls In Vitro Fecal Fermentation Rate of Insoluble Dietary Fiber from Rosa Roxburghii Tratt Pomace and Induces Butyrogenic Shifts in Microbiota Composition.

Dietary fiber has been considered a key element in shaping the beneficial host-microbe symbiosis. In the present study, we identified Rosa roxburghii Tratt fruits as a promising dietary fiber source. The physicochemical properties and in vitro fermentability by human fecal microbes of R. roxburghii pomace water insoluble dietary fiber (RIDF) obtained from ultrasonic extraction and ultrahigh pressure (90 MPa)-treated RIDF (RIDF-90) were compared to those of R. roxburghii Tratt pomace (R). Ultrahigh pressure modification significantly increased the water holding, oil holding, and swelling capacity of RIDF-90 in comparison to R and RIDF. RIDF-90 displayed the slowest fermentation rate yet yielded the highest butyrate production. The superior butyrogenic properties of both RIDF-90 and, in part, RIDF were reflected by increased Coprococcus and Ruminococcus levels, demonstrating that ultrasonic extraction and/or further ultrahigh pressure treatment of insoluble fibers promotes the prebiotic value of R. roxburghii Tratt.

Efficacy and safety of spore-forming probiotics in the treatment of functional dyspepsia: a pilot randomised, double-blind, placebo-controlled trial.

BACKGROUND: Current treatments for functional dyspepsia have limited efficacy or present safety issues. We aimed to assess spore-forming probiotics in functional dyspepsia as monotherapy or add-on therapy to long-term treatment with proton-pump inhibitors. METHODS: In this single-centre, randomised, double-blind, placebo-controlled pilot trial that took place at University Hospitals Leuven (Leuven, Belgium), adult patients (≥18 years) with functional dyspepsia (as defined by Rome IV criteria, on proton-pump inhibitors or off proton-pump inhibitors) were randomly assigned (1:1) via computer-generated blocked lists, stratified by proton-pump inhibitor status, to receive 8 weeks of treatment with probiotics (Bacillus coagulans MY01 and Bacillus subtilis MY02, 2·5 × 109 colony-forming units per capsule) or placebo consumed twice per day, followed by an open-label extension phase of 8 weeks. Individuals with a history of abdominal surgery, diabetes, coeliac or inflammatory bowel disease, active psychiatric conditions, and use of immunosuppressant drugs, antibiotics, or probiotics in the past 3 months were excluded. All patients and on-site study personnel were masked to treatment allocation in the first 8 weeks. Symptoms, immune activation, and faecal microbiota were assessed and recorded. The primary endpoint was a decrease of at least 0·7 in the postprandial distress syndrome (PDS) score of the Leuven Postprandial Distress Scale in patients with a baseline PDS score of 1 or greater (at least mild symptoms), assessed in the intention-to-treat population. This study is registered with ClinicalTrials.gov, NCT04030780. FINDINGS: Between June 3, 2019, and March 11, 2020, of 93 individuals assessed for eligibility, we included 68 patients with functional dyspepsia (51 [75%] women, mean age 40·1 years [SD 14·4], 34 [50%] on proton-pump inhibitors). We randomly assigned 32 participants to probiotics and 36 to placebo. The proportion of clinical responders was higher with probiotics (12 [48%] of 25) than placebo (six [20%] of 30; relative risk 1·95 [95% CI 1·07-4·11]; p=0·028). The number of patients with adverse events was similar with probiotics (five [16%] of 32) and placebo (12 [33%] of 36). Two serious adverse events occurring during the open-label phase (appendicitis and syncope in two separate patients) were assessed as unlikely to be related to the study product. INTERPRETATION: In this exploratory study, B coagulans MY01 and B subtilis MY02 were efficacious and safe in the treatment of functional dyspepsia. Participants had potentially beneficial immune and microbial changes, which could provide insights into possible underlying mechanisms as future predictors or treatment targets. FUNDING: MY HEALTH.

Assessment of bioaccessible and dialyzable fractions of nickel in food products and their impact on the chronic exposure of Belgian population to nickel.

This study aimed to investigate bioaccessible/dialyzable fractions of nickel in selected foods and to clarify the impact of the food digestion/absorption on the final exposure of consumers to nickel. In vitro gastrointestinal incubation experiments were conducted to estimate the bioaccessibility of nickel in different foods. For estimation of a dialyzable fraction, dialysis filtration was conducted. Highest bioaccessibility (99.6%) was observed for wheat-based breakfast cereals. Lowest bioaccessibilities was observed for dried-fruits (on average 20.4%). Highest (61.5%) and lowest (24.5%) dialyzable fractions were observed for wheat-based breakfast cereal and chocolate respectively. Bioaccessible/dialyzable fractions based exposure assessments were highlighted the overestimation of exposures calculated based on total nickel concentrations in foods. This is particularly important when exposure values were compared with toxicological thresholds in a risk characterization study. When threshold values have been obtained through animal studies in which nickel was dosed at 100% accessibility/availability, e.g. nickel salts this is even more important.

The Safety and Tolerability of a Potential Alginate-Based Iron Chelator; Results of A Healthy Participant Study.

Evidence supporting the ferro-toxic nature of iron in the progression of inflammatory bowel disease (IBD) is becoming well established. A microbial dysbiosis is observed in IBD patients, and intra-luminal colonic-iron is able to support a more pathogenic community of bacteria; whether this is attributed to the development of IBD and how iron could be mediating these microbial changes is still unknown. Dietary fibres are commonly used in pre-biotic supplements to beneficially affect the host by improving the viability of bacterial communities within the colon. Alginates are a class of biopolymers considered as prebiotics due to their fibre-like composition and are able to bind metal cations, in particular, iron. Considering that iron excess is able to negatively alter the microbiome, the use of alginate as a food supplement could be useful in colonic-iron chelation. As such, this first-in-man study aimed to assess whether the use of alginate as a dietary iron chelator was both safe and well tolerated. In addition, the impact of alginate on the microbiome and iron levels was assessed by using an intestinal model SHIME (Simulation of the Human Intestinal Microbial Ecosystem). Alginate was supplemented into the diets (3 g/day) of healthy volunteers (n = 17) for 28 days. Results from this study suggest that daily ingestion of 3 g alginate was well tolerated with very minor side effects. There were no detrimental changes in a variety of haematological parameters or the intestinal microbiome. The bacterial communities within the SHIME model were also not influenced by iron and or alginate; it is possible that alginate may be susceptible to bacterial or enzymatic degradation within the gastro-intestinal tract.

Butyrate-producing bacteria supplemented in vitro to Crohn's disease patient microbiota increased butyrate production and enhanced intestinal epithelial barrier integrity.

The management of the dysbiosed gut microbiota in inflammatory bowel diseases (IBD) is gaining more attention as a novel target to control this disease. Probiotic treatment with butyrate-producing bacteria has therapeutic potential since these bacteria are depleted in IBD patients and butyrate has beneficial effects on epithelial barrier function and overall gut health. However, studies assessing the effect of probiotic supplementation on microbe-microbe and host-microbe interactions are rare. In this study, butyrate-producing bacteria (three mono-species and one multispecies mix) were supplemented to the fecal microbial communities of ten Crohn's disease (CD) patients in an in vitro system simulating the mucus- and lumen-associated microbiota. Effects of supplementation in short-chain fatty acid levels, bacterial colonization of mucus environment and intestinal epithelial barrier function were evaluated. Treatment with F. prausnitzii and the mix of six butyrate-producers significantly increased the butyrate production by 5-11 mol%, and colonization capacity in mucus- and lumen-associated CD microbiota. Treatments with B. pullicaecorum 25-3T and the mix of six butyrate-producers improved epithelial barrier integrity in vitro. This study provides proof-of-concept data for the therapeutic potential of butyrate-producing bacteria in CD and supports the future preclinical development of a probiotic product containing butyrate-producing species.

Bioaccessibility of selenium from cooked rice as determined in a simulator of the human intestinal tract (SHIME).

BACKGROUND: As an essential but also potentially toxic element, both overexposure and underexposure to selenium (Se) can significantly affect public health. Rice is a common source of Se, especially in Asia. Not all Se may be released from the rice and become available for absorption into the bloodstream upon digestion in the gastrointestinal tract. Therefore, the bioaccessibility of Se in cooked white (polished) rice was assessed in vitro using the static gastrointestinal simulator SHIME (Simulator of the Human Intestinal Microbial Ecosystem). RESULTS: The common cooking procedure in China prior to consumption [i.e. boiling at low rice:water ratios (1:3) until all of the water is absorbed into the rice] did not change total Se levels in the rice. Gastrointestinal digestion of the cooked rice matrix revealed a Se bioaccessibility of 67-76% of total Se. Subsequent microbial activity in the colon reduced the accessibility of Se in the cooked rice to 51-62%. CONCLUSION: Not all Se present in cooked white rice should be considered as being bioavailable in the small intestine. A minor part is transferred with the remaining food matrix to the colon, where it is available for the microbial metabolism. © 2017 Society of Chemical Industry.

Towards a bacterial treatment for armpit malodour.

Axillary malodour is a frustrating condition for many people. It can lead to significant discomforts and various psychological effects. The underarm microbiome plays a major role in axillary malodour formation. Not only the bacteria on the epidermis, but also and especially those living in the sweat glands, sweat pores and hair follicles play a pivotal role in malodour development. To treat underarm malodour, this viewpoint article envisions a bacterial treatment. Replacing the autochthonous malodour-causing microbiome with a non-odour-causing microbiome, through an armpit bacterial transplantation or direct application of probiotics/non-odour-causing bacteria, could resolve the condition. Selective steering of the microbiome with prebiotics, biochemicals or plant extracts can likewise greatly help in improving the underarm odour. Elimination/inhibition of the "bad bugs" and application/stimulation of the "good bugs" will be part of the future treatment for axillary body odour.

Dietary supplement based on stilbenes: a focus on gut microbial metabolism by the in vitro simulator M-SHIME®.

Polyphenols and intestinal microbiota can influence each other, modifying metabolism and gut wellness. Data on this mutual effect need to be improved. Several studies on the biological activities of resveratrol and derivatives have been carried out, but the effects of a continuous administration of stilbenes on gut microbiota have not yet been investigated. This study evaluated the effects of an extract from Vitis vinifera, containing a combination of t-resveratrol and ε-viniferin, on intestinal microbiota, using the advanced gastrointestinal simulator M-SHIME®. A triple M-SHIME® experiment was performed using two concentrations of the extract (i.e. 1 and 2 g L-1), simulating a continuous daily intake. The effects were evaluated in terms of microbial functionality (SCFA and NH4+) and composition (DGGE and Illumina sequencing), since the microbiological aspect has been less considered so far. The treatment induced changes in microbial functionality and composition. In fact, the levels of SCFA and NH4+ suffered a strong decrease (i.e. inhibition of the saccharolytic and proteolytic activity), while DGGE and Illumina showed important modifications of the microbiota composition, associated with an imbalance of the colonic microbiota (i.e. increase in the relative abundance of Enterobacteriaceae). HPLC-DAD-TOF-MS analyses demonstrated that the metabolism of t-resveratrol and other stilbenes was inhibited by continuous administration. Our results suggest M-SHIME® as an explorative tool to define the dosage of food supplements, in particular to simulate effective continuous administration in humans.

Bioaccessibility of Polyphenols from Plant-Processing Byproducts of Black Carrot (Daucus carota L.).

Plant-processing byproducts of black carrot represent an important disposal problem for the industry; however, they are also promising sources of polyphenols, especially anthocyanins. The present study focused on the changes in polyphenols from black carrot, peel, and pomace during in vitro gastrointestinal digestion. Total phenolic content (TPC), total monomeric anthocyanin content (TMAC), and total antioxidant capacity (TAC) were determined using spectrophotometric methods, whereas identification and quantification of polyphenols were carried out using UPLC-ESI-MS(E) and HPLC-DAD, respectively. TPC, TMAC, and TAC significantly decreased (23-82%) as a result of in vitro gastrointestinal digestion. Nevertheless, the amount of pomace anthocyanins released at all stages of in vitro gastrointestinal digestion was higher than black carrot anthocyanins, suggesting that pomace may be a better source of bioaccessible anthocyanins. Overall, the current study highlighted black carrot byproducts as substantial sources of polyphenols, which may be used to enrich food products.

Selenium bioaccessibility in stomach, small intestine and colon: Comparison between pure Se compounds, Se-enriched food crops and food supplements.

Selenium (Se) is an essential nutrient for humans as it plays an important role in glutathione peroxidase (GPx) activity. Moreover, it may reduce cancer risks. The objective of this work was to examine in vitro the bioaccessibility of Se in three different Se-enriched food supplements and two different Se-enriched food crops, with reference to two pure Se standards, and changes in its speciation during intestinal digestion. Selenate was found to be stable throughout the entire digestion, whereas incubation of selenomethionine resulted in the chemical and microbial production of minor metabolites. The bioaccessibility of Se in Se-enriched food supplements and food crops was found to be highest in the small intestine. Compared to SelenoPrecise and Se-ACE tablets, a yoghurt-based supplement exhibited a much lower Se bioaccessibility, possibly due to the presence of nano- or microparticles of elemental Se. Colon microbiota were found to primarily affect Se bioaccessibility in the colon environment, with the presence of inactivated microbiota resulting in a higher bioaccessibility. A higher potential of Se to reach the colon and become accessible in this phase may result in beneficial effects on the colon health.

Comparative in vitro fermentations of cranberry and grape seed polyphenols with colonic microbiota.

In this study, we have assessed the phenolic metabolism of a cranberry extract by microbiota obtained from the ascending colon and descending colon compartments of a dynamic gastrointestinal simulator (SHIME). For comparison, parallel fermentations with a grape seed extract were carried out. Extracts were used directly without previous intestinal digestion. Among the 60 phenolic compounds targeted, our results confirmed the formation of phenylacetic, phenylpropionic and benzoic acids as well as phenols such as catechol and its derivatives from the action of colonic microbiota on cranberry polyphenols. Benzoic acid (38.4µg/ml), 4-hydroxy-5-(3'-hydroxyphenyl)-valeric acid (26.2µg/ml) and phenylacetic acid (19.5µg/ml) reached the highest concentrations. Under the same conditions, microbial degradation of grape seed polyphenols took place to a lesser extent compared to cranberry polyphenols, which was consistent with the more pronounced antimicrobial effect observed for the grape seed polyphenols, particularly against Bacteroides, Prevotella and Blautia coccoides-Eubacterium rectale.

Metabolic fate of ochratoxin A as a coffee contaminant in a dynamic simulator of the human colon.

Ochratoxin A (OTA) is a mycotoxin frequently encountered in coffee. The relevance of this contaminant in the colon upon digestion necessitates a study on its interaction with colon microbiota. Here, the fate of OTA during colon digestion was investigated using a dynamic simulator of the human gut. The influence of coffee as a food matrix was taken into account, as it may affect the colonic microbial ecosystem and, consequently, the fate of OTA. Biodegradation was followed by measuring OTA concentration over time, and by screening for several possible metabolites, using LC-ESI-MS and HRMS. The descending colon was found to be the main site of OTA biodegradation. Two metabolites, ochratoxin α and ochratoxin B, were identified, suggesting that biodegradation by gut microbiota is beneficial for the host, as they are considered less toxic than OTA. The extent of biodegradation was reduced in the presence of the coffee matrix, possibly due to competition for available carbon sources. Effects of OTA and the coffee matrix on the microbial ecosystem were contrasting. While OTA caused a specific, but lasting loss, of the beneficial species Lactobacillus reuteri, coffee temporarily altered the fermentation pattern towards lower ammonia and higher acetate and propionate production, likely due to its dietary fibre content.

Incubation of selected fermentable fibres with feline faecal inoculum: correlations between in vitro fermentation characteristics and end products.

This study aimed to evaluate correlations between fermentation characteristics and end products of selected fermentable fibres (three types of fructans, citrus pectin, guar gum), incubated with faecal inocula from donor cats fed two diets, differing in fibre and protein sources and concentrations. Cumulative gas production was measured over 72 h, fermentation end products were analysed at 4, 8, 12, 24, 48 and 72 h post-incubation, and quantification of lactobacilli, bifidobacteria and bacteroides in fermentation liquids were performed at 4 and 48 h of incubation. Partial Pearson correlations, corrected for inoculum, were calculated to assess the interdependency of the fermentation characteristics of the soluble fibre substrates. Butyric and valeric acid concentrations increased with higher fermentation rates, whereas acetic acid declined. Concentrations of butyric acid (highest in fructans) and propionic acid were inversely correlated with protein fermentation end products at several time points, whereas concentrations of acetic acid (highest in citrus pectin) were positively correlated with these products at most time points. Remarkably, a lack of clear relationship between the counts of bacterial groups and their typically associated products after 4 h of incubation was observed. Data from this experiment suggest that differences in fibre fermentation rate in feline faecal inocula coincide with typical changes in the profile of bacterial fermentation products. The observed higher concentrations of propionic and butyric acid as a result of fibre fermentation could possibly have beneficial effects on intestinal health, and may be confounded with a concurrent decrease in the production of putrefactive compounds. In conclusion, supplementing guar gum or fructans to a feline diet might be more advantageous compared with citrus pectin. However, in vivo research is warranted to confirm these conclusions in domestic cats.

Trace metals accumulation in Bacopa monnieri and their bioaccessibility.

Bacopa monnieri is commonly known as "Brahmi" or "Water hyssop" and is a source of nootropic drugs. Aboveground parts of plant samples collected from peri-urban Indian areas were analysed for total trace metal concentrations. Subsequently, three samples with high concentrations of Cd and Pb were subjected to in vitro gastrointestinal digestion to assess the bioaccessibility of the trace metals in these plants. The total concentrations of trace metals on a dry weight basis were 1.3 to 6.7 mg·kg⁻¹ Cd, 1.5 to 22 mg·kg⁻¹ Pb, 36 to 237 mg·kg⁻¹ Cu, and 78 to 186 mg·kg⁻¹ Zn. The majority of Bacopa monnieri samples exceeded threshold limits of Cd, Pb, Cu, and Zn for use as raw medicinal plant material or direct consumption. Therefore, it is necessary to evaluate Bacopa monnieri collected in nature for their trace metal content prior to human consumption and preparation of herbal formulations.

Prebiotics, faecal transplants and microbial network units to stimulate biodiversity of the human gut microbiome.

Accumulating evidence demonstrates the intimate association between human hosts and the gut microbiome. Starting at birth, the sterile gut of the newborn acquires a diverse spectrum of microbes, needed for immunological priming. However, current practices (caesarean sections, use of formula milk) deprive newborns from being exposed to this broad spectrum of microbes. Unnecessary use of antibiotics and excessive hygienic precautions (e.g. natural versus chlorinated drinking water) together with the Western diet further contribute to a decreased microbial diversity in the adult gut. This has been correlated with recurrent Clostridium difficile infection, inflammatory bowel diseases and obesity, among others. A healthy gut microbiome is thus characterized by a diverse network of metabolically interacting microbial members. In this context, we review several existing and novel approaches to manage the gut microbiome. First, prebiotic compounds should be re-defined in the sense that they should enhance the ecological biodiversity rather than stimulating single species. Recent studies highlight that structurally different polysaccharides require specific primary degraders but also enhance a similar network of secondary degraders that benefit from cross-feeding. A faecal transplantation is a second approach to restore biodiversity when the microbiota is severely dysbiosed, with promising results regarding C. difficile-associated disease and obesity-related metabolic syndromes. A final strategy is the introduction of key microbial network units, i.e. pre-organized microbial associations, which strengthen the overall microbial network of the gut microbiome that supports human health.

Implication of fermentable carbohydrates targeting the gut microbiota on conjugated linoleic acid production in high-fat-fed mice.

In vitro experiments have shown that isolated human gut bacteria are able to metabolise PUFA into conjugated PUFA like conjugated linoleic acids (CLA). The hypothesis of the present paper was that high-fat (HF) diet feeding and supplementation with fermentable carbohydrates that have prebiotic properties modulate the in vivo production of CLA by the mouse gut microbiota. Mice were treated for 4 weeks as follows: control (CT) groups were fed a standard diet; HF groups were fed a HF diet rich in linoleic acid (18 : 2n-6); the third groups were fed with the HF diet supplemented with either inulin-type fructans (HF-ITF) or arabinoxylans (HF-Ax). HF diet feeding increased rumenic acid (cis-9,trans-11-18 : 2 CLA) content both in the caecal and liver tissues compared with the CT groups. ITF supplementation had no major effect compared with the HF diet whereas Ax supplementation increased further rumenic acid (cis-9,trans-11-18 : 2 CLA) in the caecal tissue. These differences between both prebiotics may be linked to the high fat-binding capacity of Ax that provides more substrates for bacterial metabolism and to differential modulation of the gut microbiota (specific increase in Roseburia spp. in HF-Ax v. HF). In conclusion, these experiments supply the proof of concept that the mouse gut microbiota produces CLA in vivo, with consequences on the level of CLA in the caecal and liver tissues. We postulate that the CLA-producing bacteria could be a mediator to consider in the metabolic effects of both HF diet feeding and prebiotic supplementation.

Gut metabotypes govern health effects of dietary polyphenols.

Polyphenols are thought to be responsible for some of the health effects conferred by a diet rich in fruit and vegetables. Both the formation of bioactive polyphenol-derived metabolites and the modulation of colonic microbiota contribute to these health benefits. Therefore, one cannot infer biological responses from dietary intake records without considering polyphenol-microbiota interactions. However, the latter are complex and subject to large interindividual variability, leading to different polyphenol-metabolizing phenotypes or 'metabotypes'. Based on accurate measurements of intake, exposure and effect on carefully selected samples, the physiological relevance of dietary polyphenols can be evaluated for each metabotype. Ultimately, this will lead to predictive modeling and the development of (personalized) functional foods and other nutraceuticals with maximized health benefits.

Fertilizing soil with selenium fertilizers: impact on concentration, speciation, and bioaccessibility of selenium in leek (Allium ampeloprasum).

Leek was fertilized with sodium selenite (Na(2)SeO(3)) and sodium selenate (Na(2)SeO(4)) in a green house to assess the impact of selenium (Se) fertilization on Se uptake by the crop and its speciation in the crop. The bioaccessibility of Se in the Se-enriched leek was assessed using an in vitro extraction protocol mimicking the human gastrointestinal tract (stomach, small intestine, and colon). The lowest Se uptake was observed when Na(2)SeO(3) was used as a fertilizer, which results in a higher risk for Se accumulation in the soil on a longer term. When soil was amended with Na(2)SeO(4), 55 ± 5% of total Se in the leek occurred in an inorganic form, while only 21 ± 8% was inorganic when Na(2)SeO(3) was applied. Se-methylselenocysteine and selenomethione were the major organic species in both treatments. However, concentrations of Se-methylselenocysteine and γ-glutamyl-Se-methyl-selenocysteine, which were previously reported to induce positive health effects, were lower as compared to other Allium species. The majority of the Se in the leek was found to be bioaccessible in the stomach (around 60%) and small intestine (around 80%). However, a significant fraction also has good chances to reach the colon, where it seems to be taken up by the microbial community and may also induce positive health effects.