The public health rationale for increasing dietary fibre: Health benefits with a focus on gut microbiota

Dietary fibre can be considered an essential macronutrient which feeds our gut microbiota, thus enabling the optimal functioning of this ‘virtual organ’. Recommended daily intakes range from 25 to 38 g/day. However, most individuals fail to reach this target and may consume <50% of the recommended amount. Poor dietary fibre intake is associated with an imbalanced gut microbiota leading to reduced diversity and increased abundance of non‐beneficial microorganisms at the expense of beneficial ones. Inflammation is a recognised physiological effect of such a microbiome structure and is a common denominator in several non‐communicable diseases associated with the Western lifestyle/developed world including obesity, cardiovascular disease, type 2 diabetes and colorectal cancer. Yet increasing dietary fibre intake can reduce risk factors associated with these diseases and may even improve prognosis. Several food manufacturers have now developed strategies to increase the fibre content of foods. However, research gaps still remain. In particular, dietary fibre is composed of various non‐digestible carbohydrates and the exact effect of each of these on the gut microbiota is currently unknown. The links between dietary fibre and disease risk are generally associative. Understanding the biological mechanisms will require deeper insight into the impact of the gut microbiota on health. Furthermore, gut microbiota research has shown significant inter‐individual variation meaning that some individuals may not respond to certain dietary fibres owing to the absence of specific microorganisms. Understanding how the different fibre types influence the microbiota, combined with knowledge of an individual’s microbiota, should lead to fibre‐led, microbiota‐based dietary advice.     

Dietary Vitamin B1 Intake Influences Gut Microbial Community and the Consequent Production of Short-Chain Fatty Acids

The gut microbiota is closely related to good health; thus, there have been extensive efforts dedicated to improving health by controlling the gut microbial environment. Probiotics and prebiotics are being developed to support a healthier intestinal environment. However, much work remains to be performed to provide effective solutions to overcome individual differences in the gut microbial community. This study examined the importance of nutrients, other than dietary fiber, on the survival of gut bacteria in high-health-conscious populations. We found that vitamin B1, which is an essential nutrient for humans, had a significant effect on the survival and competition of bacteria in the symbiotic gut microbiota. In particular, sufficient dietary vitamin B1 intake affects the relative abundance of Ruminococcaceae, and these bacteria have proven to require dietary vitamin B1 because they lack the de novo vitamin B1 synthetic pathway. Moreover, we demonstrated that vitamin B1 is involved in the production of butyrate, along with the amount of acetate in the intestinal environment. We established the causality of possible associations and obtained mechanical insight, through in vivo murine experiments and in silico pathway analyses. These findings serve as a reference to support the development of methods to establish optimal intestinal environment conditions for healthy lifestyles.     

Dietary Fiber Intake Alters Gut Microbiota Composition but Does Not Improve Gut Wall Barrier Function in Women with Future Hypertensive Disorders of Pregnancy

Pregnancy alters the inflammatory state, metabolic hormones, and gut microbiota composition. It is unclear if the lower abundance of dietary fiber-fermenting, short-chain fatty acid-producing bacteria observed in hypertension also occurs in hypertensive disorders of pregnancy (HDP). This study investigated the relationship between dietary fiber intake and the gut microbiota profile at 28 weeks gestation in women who developed HDP in late pregnancy (n = 22) or remained normotensive (n = 152) from the Study of PRobiotics IN Gestational diabetes (SPRING). Dietary fiber intake was classified as above or below the median of 18.2 g/day. Gut microbiota composition was examined using 16S rRNA gene amplicon sequencing. The gut permeability marker zonulin was measured in a subset of 46 samples. In women with future HPD, higher dietary fiber intake was specifically associated with increased abundance of Veillonella, lower abundance of Adlercreutzia, Anaerotruncus and Uncl. Mogibacteriaceae and higher zonulin levels than normotensive women. Fiber intake and zonulin levels were negatively correlated in women with normotensive pregnancies but not in pregnancies with future HDP. In women with normotensive pregnancies, dietary fiber intake may improve gut barrier function. In contrast, in women who develop HDP, gut wall barrier function is impaired and not related to dietary fiber intake.     

2型糖尿病患者膳食纤维摄入量与肠道菌群的关联——基于一项随机对照试验的数据再分析

目的 分析2型糖尿病患者膳食纤维摄入量与肠道菌群的关联,发现相关差异菌群,为改善患者日常饮食,调节肠道菌群,促进健康提供依据。方法 采用横断面研究设计,以参与一项健康素养和体力活动干预随机对照试验的356名2型糖尿病患者为研究对象。总热能和膳食纤维摄入量基于3 d 24 h膳食调查数据和中国食物成分表计算。对粪便菌群DNA进行16S rDNA V4高变区测序,采用Qiime2软件进行生物信息学分析。多变量线性回归模型(multivariate analysis by linear models, MaAsLin)方法和广义线性模型用于获得与膳食纤维摄入量有关的肠道菌群。结果 研究对象的膳食纤维摄入量处于较低水平,中位摄入量(四分位间距)仅7.4(5.5, 9.7) g/d。未发现膳食纤维摄入量高低与肠道菌群Alpha多样性有关,但基于Jaccard距离矩阵(PERMANOVA P=0.016)计算的Beta多样性在两组间差异有统计学意义。低膳食纤维摄入组有较高丰度的梭杆菌属(Fusobacterium)、柯林斯菌属(Collinsella)和普雷沃菌属(Prevotella),而高膳食...     

Chewing the Fat with Microbes: Lipid Crosstalk in the Gut

It is becoming increasingly important for any project aimed at understanding the effects of diet on human health, to also consider the combined effect of the trillions of microbes within the gut which modify and are modified by dietary nutrients. A healthy microbiome is diverse and contributes to host health, partly via the production and subsequent host absorption of secondary metabolites. Many of the beneficial bacteria in the gut rely on specific nutrients, such as dietary fiber, to survive and thrive. In the absence of those nutrients, the relative proportion of good commensal bacteria dwindles while communities of opportunistic, and potentially pathogenic, bacteria expand. Therefore, it is unsurprising that both diet and the gut microbiome have been associated with numerous human diseases. Inflammatory bowel diseases and colorectal cancer are associated with the presence of certain pathogenic bacteria and risk increases with consumption of a Western diet, which is typically high in fat, protein, and refined carbohydrates, but low in plant-based fibers. Indeed, despite increased screening and better care, colorectal cancer is still the 2nd leading cause of cancer death in the US and is the 3rd most diagnosed cancer among US men and women. Rates are rising worldwide as diets are becoming more westernized, alongside rising rates of metabolic diseases like obesity and diabetes. Understanding how a modern diet influences the microbiota and how subsequent microbial alterations effect human health will become essential in guiding personalized nutrition and healthcare in the future. Herein, we will summarize some of the latest advances in understanding of the three-way interaction between the human host, the gut microbiome, and the specific class of dietary nutrients, lipids.     

Dietary fibre and the gut microbiota

Summary The complex human colonic microbiota plays a key role in gut health, and both the composition and metabolism of the gut microbiota are strongly diet related. Controlled dietary intake studies in obese individuals demonstrated that consumption of low‐carbohydrate diets results in low faecal butyrate concentrations together with a low abundance of the major butyrate‐producing bacteria, Roseburia spp. and Eubacterium rectale group. Resistant dietary carbohydrates, including pre‐biotics, escape digestion in the upper gastrointestinal tract and are fermented to short‐chain fatty acids (SCFAs) by bacteria in the colon. The main SCFAs formed are acetate, propionate and butyrate. Model colonic fermentor systems employed to determine which bacterial groups utilise specific substrates indicated that the bacterial composition and production of SCFAs is substrate dependent. The bacterial colonisers of specific substrates were identified using 16S rRNA sequence analysis. Sequences recovered from bran were most closely related to Roseburia spp., E. rectale and Clostridium hathewayi, while on resistant starch, sequences were most closely related to Ruminococcus bromii and Bifidobacterium adolescentis. Differing intakes of dietary carbohydrate also impact on other factors in the colon such as transit and pH. In continuous fermentor systems, a slightly acidic pH (5.5) representative of the proximal colon gave fourfold higher butyrate concentrations than at the higher pH of 6.5, which is more representative of the distal colon. Bacteroidetes dominated the fermentor at pH 6.5, while the major butyrate‐producing bacterial groups competed more effectively for carbohydrate substrates when the pH was mildly acidic (5.5). In in vitro studies in which pH values were even lower, pH 5.2, lactate and acetate accumulated. In contrast, lactate was not detected at pH 6.4 although stable isotope studies revealed that lactate was actively produced. Lactate accumulation at low pH appears to be as a result of the loss of lactate‐utilising bacteria including Eubacterium hallii. It is clear that the composition of the colonic microbiota and the balance of its metabolic products is strongly influenced by diet and, in particular, by the intake of resistant carbohydrates and dietary fibre.     

Dietary Whole Grain–Microbiota Interactions: Insights into Mechanisms for Human Health

This article summarizes the presentations from the “Dietary Whole Grain–Microbiota Interactions: Insights into Mechanisms for Human Health” symposium held at the ASN Scientific Sessions and Annual Meeting at Experimental Biology 2014 in San Diego, CA, on 28 April 2014. The symposium focused on the interactive effects of whole grains and nondigestible carbohydrates with the gut microbiota with the goal of identifying the benefits of whole grains that are mediated through their effects on the gut microbiome. This theme was addressed by 4 speakers, each with their own unique perspective. Dr. Michael Lefevre reviewed the impact of whole grains on markers of subclinical inflammation, drawing examples from epidemiologic literature, clinical trials, and animal experiments. Dr. Knud Erik Bach Knudsen discussed data from studies he conducted to identify specific carbohydrates that enhance colonic butyrate production. Dr. Michael Keenan presented a chronology of his research program devoted to understanding the mechanisms underlying the metabolic effects of resistant starch, particularly high-amylose maize. Dr. Jens Walter emphasized that whole grains can impact gut microbial ecology by increasing microbial diversity and inducing compositional alterations, some of which are considered to have beneficial effects on the host.The concept of microbial-mammalian cometabolism as a key influence on human health is a hot topic that involves the integration of nutrition, metabolomics, microbiology, genomics/metagenomics, and food science. The role of the gut microbiome in optimizing health has received considerable attention in the nutrition community. Rather than review the sweeping research efforts in this rapidly expanding field, this symposium, entitled “Dietary Whole Grain–Microbiota Interactions: Insights into Mechanisms for Human Health,” focused on the interactive effects of whole grains and nondigestible carbohydrates with the gut microbiota with the goal of identifying the benefits of whole grains that are mediated through their effects on the gut microbiome. The objectives of this symposium were as follows: 1) to understand the current research methods used to study nutrition and gut microbiota; 2) to understand the roles of particular bacteria in the microbial community of the human large intestine; and 3) to present novel hypotheses related to the role of gut microbiota in improved human health. Four distinguished speakers addressed the symposium theme, each providing their own unique perspective, describing cutting-edge science in this field and testing key hypotheses relative to the mechanisms of the well-known health benefits of whole grains.The symposium’s first speaker was Dr. Michael Lefevre, USTAR Professor at Utah State University’s Center for Human Nutrition Studies and the Scientific Director of the Applied Nutrition Research team. Lefevre’s presentation, “Whole grains and markers of subclinical inflammation,” first reviewed epidemiologic evidence of the role of whole grains in promoting good health and affecting disease risk specific to inflammation. Cohort studies reveal that small changes in risk could be attributable to whole-grain consumption, but interpretation of this effect is confounded by the possibility that use of whole grains may indicate a healthier lifestyle. In contrast to epidemiologic studies, interventional studies do not demonstrate a clear effect of increased whole-grain consumption on markers of inflammation. Only 1 study found a decrease in circulating C-reactive protein concentrations, whereas all other studies reviewed found no change in markers of inflammation. Issues related to insufficient length of intervention, extent of dietary control, population selection, types of whole grains, and lack of a direct anti-inflammatory effect may underlie these discrepant findings. These findings have been summarized previously in a published review article (1). In particular, he emphasized that one cannot assume that all whole grains have similar physiologic effects. New research conducted in his laboratory demonstrates that whole wheat, whole oats, and whole corn have unique effects on inflammatory responses, metabolism, and gut microbiota composition.The second speaker was Dr. Knud Erik Bach Knudsen, Professor and Head of the Research Unit on Molecular Nutrition and Cell Biology in the Department of Animal Science, Aarhus University, Denmark. In his presentation, “Microbial degradation and impact on short-chain fatty acids of whole grain complex carbohydrates in the gut,” Knudsen posited that the carbohydrates found in cereals may have major effects on butyrate production in the large intestine and described a series of studies he conducted to identify specific carbohydrates that enhance colonic butyrate production. Butyrate is targeted for its beneficial effects on gut health, including maintaining the integrity of the coloncytes. Systemically, this short-chain FA may also promote insulin sensitivity and glucose homeostasis and reduce food intake through release of gut peptides associated with satiety. Knudsen has found that arabinoxylan-rich rye fractions produce the highest level of colonic butyrate production and explained how this carbohydrate source might be used to improve health.The third speaker was Dr. Michael J. Keenan, Associate Professor of Human Ecology at the Louisiana Agricultural Experimental Station at Louisiana State University, Baton Rouge, LA. Keenan’s presentation, “Role of resistant starch in improving gut health and metabolic syndrome,” included a chronology of his research program devoted to understanding the mechanisms underlying the metabolic effects of resistant starch, particularly high-amylose maize. He has studied the impact of resistant starches from grains on gut microbial profiles and markers of health in gestational diabetes and in both dietary and genetic animal models of obesity. The primary event in resistant starch action is the manipulation of the gut microbiome and resulting fermentation products. Keenan reported that microbial community shifts associated with resistant starch consumption include increases in Lactobacillus, Bifidobacterium, and Akkermansia. Along with these shifts in microbiota, insulin sensitivity improves, possibly due to these following secondary mechanisms: 1) improved gut health and gut barrier function, which lowers the leakage of inflammatory products from the gut to the blood stream; and/or 2) butyrate stimulation of enteroendocrine cells to increase production and secretion of glucagon-like peptide 1, which is known to improve insulin sensitivity and reduce body fat.The fourth speaker was Dr. Jens Walter, Associate Professor and Campus Alberta Innovation Program Chair for Nutrition, Microbes, and Gastrointestinal Health at the University of Alberta, Edmonton, Canada. Walter’s presentation, “The role of the gastrointestinal microbiota in the health benefits of whole grains,” began with the suggestion that dysbiosis of the intestinal microbiota is associated with a large number of the chronic diseases prevalent in Western societies. This dysbiosis, characterized by decreased diversity of the microbiota, is the result of a modern lifestyle that includes a diet low in fiber and high in simple sugars, fats, and protein—a diet that provides poor nutritional support for microbes inhabiting the large intestine. Walter emphasized that whole grains can impact gut microbial ecology by increasing microbial diversity and inducing compositional alterations, some of which are considered to have beneficial effects on the host. For example, in studies with whole-grain barley, brown rice, and the combination of these grains, he found that inclusion of both whole grains led to increases in the Firmicutes:Bacteroidetes ratio. Also, he found that whole-grain barley consumption resulted in enrichments of the genera Roseburia, Bifidobacterium, and Dialister, and the species Eubacterium rectale, Roseburia faecis, and Roseburia intestinalis. These changes were seen despite large interindividual variation in response to the whole grains. The grain combination also produced decreases in peak postprandial glucose and plasma IL-6; the latter decrease was related to abundance of specific taxa.In summary, new data were presented to demonstrate that consumption of whole grains and complex nondigestible carbohydrates found in whole grains can significantly shift the microbial ecology of the large bowel. These changes were associated with alterations in markers of immunologic function and with improvements in blood glucose control. Collectively, the speakers presented state-of-the-art concepts aimed to determine the role of the gut microbiota in conferring health benefits of whole grains. Important themes highlighted by these presentations were as follows: 1) the carbohydrates contained in whole grains vary in complexity and structure and, as a result, have different effects on the microbiota; 2) other diet components such as fat or protein may influence the response to whole grains; and 3) individual responses to whole grains are varied and influenced by phenotype and genotype. We were also reminded that, in addition to the complex carbohydrates, whole grains contain other bioactive components, such as lignans and polyphenols, that may influence metabolic and immunologic functions independently or in concert with shifts in the microbiota. Clearly, many questions remain to be answered, but the work presented by our speakers has established a strong foundation for future exploration of whole grain–microbiota interactions.     

Immunological aspects of the potential role of dietary carbohydrates and lectins in human health

Summary Background: Little is known regarding the immunobiology of dietary carbohydrate intake and its relevance to human health, although foodstuffs contain many simple and complex carbohydrates. Synopsis: Lectins, immunoglobulins, viruses, bacteria and host cells interact with each other forming a delicate equilibrium within the alimentary canal which may be perturbed by saccharide intake. The ways in which these components may interact at different sites within the alimentary canal are discussed, as are the possible influences on mucosal immunity and the induction of oral tolerance. The possible systemic influences of absorbed saccharides at loci remote from the gut are considered in terms of inhibition of dietary and endogenous lectins, inhibition of bacterial attachment, and alteration of leukocyte homing behaviour. Finally, possible means by which dietary carbohydrates might modify various specific diseases are considered. Conclusions: It is probable that dietary carbohydrates can alter the equilibria between lectins, secretory IgA and micro-organisms in the alimentary canal, and this consideration could be exploited to promote health. The possible effects of dietary saccharides on allergy/oral tolerance or on recognition events at gut-remote sites warrant further investigation. Received: 15 December 1998, Accepted: 15 March 1999     

The Influence of Early Life Nutrition on Epigenetic Regulatory Mechanisms of the Immune System

The immune system is exquisitely sensitive to environmental changes. Diet constitutes one of the major environmental factors that exerts a profound effect on immune system development and function. Epigenetics is the study of mitotically heritable, yet potentially reversible, molecular modifications to DNA and chromatin without alteration to the underlying DNA sequence. Nutriepigenomics is an emerging discipline examining the role of dietary influences on gene expression. There is increasing evidence that the epigenetic mechanisms that regulate gene expression during immune differentiation are directly affected by dietary factors or indirectly through modifications in gut microbiota induced by different dietary habits. Short-chain fatty acids, in particular butyrate, produced by selected bacteria stains within gut microbiota, are crucial players in this network.     

Gut microbiota functions: metabolism of nutrients and other food components

The diverse microbial community that inhabits the human gut has an extensive metabolic repertoire that is distinct from, but complements the activity of mammalian enzymes in the liver and gut mucosa and includes functions essential for host digestion. As such, the gut microbiota is a key factor in shaping the biochemical profile of the diet and, therefore, its impact on host health and disease. The important role that the gut microbiota appears to play in human metabolism and health has stimulated research into the identification of specific microorganisms involved in different processes, and the elucidation of metabolic pathways, particularly those associated with metabolism of dietary components and some host-generated substances. In the first part of the review, we discuss the main gut microorganisms, particularly bacteria, and microbial pathways associated with the metabolism of dietary carbohydrates (to short chain fatty acids and gases), proteins, plant polyphenols, bile acids, and vitamins. The second part of the review focuses on the methodologies, existing and novel, that can be employed to explore gut microbial pathways of metabolism. These include mathematical models, omics techniques, isolated microbes, and enzyme assays.     

Protein Intake,Metabolic Status and the Gut Microbiota in Different Ethnicities: Results from Two Independent Cohorts

Background: Protein intake has been associated with the development of pre-diabetes (pre-T2D) and type 2 diabetes (T2D). The gut microbiota has the capacity to produce harmful metabolites derived from dietary protein. Furthermore, both the gut microbiota composition and metabolic status (e.g., insulin resistance) can be modulated by diet and ethnicity. However, to date most studies have predominantly focused on carbohydrate and fiber intake with regards to metabolic status and gut microbiota composition. Objectives: To determine the associations between dietary protein intake, gut microbiota composition, and metabolic status in different ethnicities. Methods: Separate cross-sectional analysis of two European cohorts (MetaCardis, n = 1759; HELIUS, n = 1528) including controls, patients with pre-T2D, and patients with T2D of Caucasian/non-Caucasian origin with nutritional data obtained from Food Frequency Questionnaires and gut microbiota composition. Results: In both cohorts, animal (but not plant) protein intake was associated with pre-T2D status and T2D status after adjustment for confounders. There was no significant association between protein intake (total, animal, or plant) with either gut microbiota alpha diversity or beta diversity, regardless of ethnicity. At the species level, we identified taxonomical signatures associated with animal protein intake that overlapped in both cohorts with different abundances according to metabolic status and ethnicity. Conclusions: Animal protein intake is associated with pre-T2D and T2D status but not with gut microbiota beta or alpha diversity, regardless of ethnicity. Gut microbial taxonomical signatures were identified, which could function as potential modulators in the association between dietary protein intake and metabolic status.     

Microbiota and Metabolite Modifications after Dietary Exclusion of Dairy Products and Reduced Consumption of Fermented Food in Young and Older Men

The gut microbiota adapts to age-related changes in host physiology but is also affected by environmental stimuli, like diet. As a source of both pre- and probiotics, dairy and fermented foods modulate the gut microbiota composition, which makes them interesting food groups to use for the investigation of interactions between diet and ageing. Here we present the effects of excluding dairy products and limiting fermented food consumption for 19 days on gut microbiota composition and circulating metabolites of 28 healthy, young (YA) and older (OA) adult men. The intervention affected gut microbial composition in both groups, with significant increases in Akkermansia muciniphila and decreases in bacteria of the Clostridiales order. Lower fasting levels of glucose and insulin, as well as dairy-associated metabolites like lactose and pentadecanoic acid, were observed after the intervention, with no effect of age. The intervention also decreased HDL and LDL cholesterol levels. Dairy fat intake was positively associated with the HDL cholesterol changes but not with the LDL/HDL ratio. In conclusion, restricting the intake of dairy and fermented foods in men modified their gut microbiota and blood metabolites, while the impact of the dietary restrictions on these outcomes was more marked than the effect of age.     

Lipides et inflammation postprandiale : impact du microbiote intestinal

Obesity and type 2 diabetes are associated with low-grade inflammatory tone. Growing evidence demonstrates that the gut microbiota is involved not only in the host metabolism but also in the pathogenesis of the low grade inflammation associated with obesity and type 2 diabetes. Among the mechanisms, dietary habits and more specifically the nutritional composition of the diet (lipids, non-digestible carbohydrates) have been shown to participate to the modulation of the composition and the activity of the gut microbiota. These questions and mechanisms will be discussed following experimental data.     

Nutrient Intake and Gut Microbial Genera Changes after a 4-Week Placebo Controlled Galacto-Oligosaccharides Intervention in Young Females

Recent interest in the gut-brain-axis has highlighted the potential of prebiotics to impact wellbeing, and to affect behavioral change in humans. In this clinical trial, we examined the impact of four-weeks daily supplementation of galacto-oligosaccharides (GOS) on self-reported nutrient intake and relationships on gut microbiota in a four-week two-armed parallel double-blind placebo controlled GOS supplement trial in young adult females. Food diaries and stool samples were collected prior to and following 28 days of supplement consumption. It was found that four weeks of GOS supplementation influenced macronutrient intake, as evident by reduced carbohydrate and sugars and increased fats intake. Further analysis showed that the reduction in carbohydrates was predicted by increasing abundances of Bifidobacterium in the GOS group in comparison to the placebo group. This suggests that Bifidobacterium increase via GOS supplementation may help improve the gut microbiota composition by altering the desire for specific types of carbohydrates and boosting Bifidobacterium availability when fiber intake is below recommended levels, without compromising appetite for fiber from food.     

Role of Oral and Gut Microbiota in Dietary Nitrate Metabolism and Its Impact on Sports Performance

Nitrate supplementation is an effective, evidence-based dietary strategy for enhancing sports performance. The effects of dietary nitrate seem to be mediated by the ability of oral bacteria to reduce nitrate to nitrite, thus increasing the levels of nitrite in circulation that may be further reduced to nitric oxide in the body. The gut microbiota has been recently implicated in sports performance by improving muscle function through the supply of certain metabolites. In this line, skeletal muscle can also serve as a reservoir of nitrate. Here we review the bacteria of the oral cavity involved in the reduction of nitrate to nitrite and the possible changes induced by nitrite and their effect on gastrointestinal balance and gut microbiota homeostasis. The potential role of gut bacteria in the reduction of nitrate to nitrite and as a supplier of the signaling molecule nitric oxide to the blood circulation and muscles has not been explored in any great detail.     

Habitual Diet Pattern Associations with Gut Microbiome Diversity and Composition: Results from a Chinese Adult Cohort

The influence of long-term diet on gut microbiota is an active area of investigation. The present work aimed to explore the associations between habitual diet patterns and gut microbiota in a large sample of asymptomatic Chinese adults. The gut microbiome was profiled through the sequencing of the 16S rRNA gene in stool samples from 702 Chinese adults aged 50–75 years who underwent colonoscopies and were diagnosed to be free of colorectal neoplasm. Long-term dietary consumption was assessed through a food-frequency questionnaire. The microbial associations with specific food groups and the posteriori dietary pattern were tested using the Kruskal–Wallis H test, permutational ANOVAs, and multivariate analyses with linear models. The Shannon indexes generally shared similar levels across different food intake frequency groups. Whole grain and vegetable intakes totally explained 1.46% of the microbiota compositional variance. Using the data-driven posteriori approach, a general dietary pattern characterized by lower intakes of refined grains was highlighted to be associated with higher abundances of the genus Anaerostipes and a species of it. We also observed 17 associations between various food group intakes and specific genera and species. For instance, the relative abundances of the genus Weissella and an uncultured species of it were negatively associated with red meat intake. The results of this study support the idea that the usual dietary consumption measured by certain food items or summary indexes is associated with gut microbial features. These results deepen the understanding of complex relationships of diet and gut microbiota, as well as their implications for gut microbiome studies of human chronic diseases.     

Role of dietary beta-glucans in the prevention of the metabolic syndrome

The present review examines the evidence regarding the effect of β-glucan on variables linked to the metabolic syndrome (MetS), including appetite control, glucose control, hypertension, and gut microbiota composition. Appetite control can indirectly influence MetS by inducing a decreased energy intake, and promising results for a β-glucan intake to decrease appetite have been found using gut hormone responses and subjective appetite indicators. Beta-glucan also improves the glycemic index of meals and beneficially influences glucose metabolism in patients with type 2 diabetes or MetS, as well as in healthy subjects. Furthermore, a blood-pressure-lowering effect of β-glucan in hypertensive subjects seems fairly well substantiated. The gut microbiota composition might be an interesting target to prevent MetS, and preliminary results indicate the prebiotic potential of β-glucan. The evidence that β-glucan influences appetite control and gut microbiota in a positive way is still insufficient or difficult to interpret, and additional studies are needed in this field. Still, much evidence indicates that increased β-glucan intake could prevent MetS. Such evidence should encourage increased efforts toward the development of β-glucan-containing functional foods and promote the intake of β-glucan-rich foods, with the aim of reducing healthcare costs and disease prevalence.     

Influence of Mediterranean Diet on Human Gut Microbiota

Gut microbiota changes correlate with health status. Literature data on gut microbiota show that all dietary changes can induce the alteration of gut microbiota composition. Mediterranean diet (MD) is associated with a reduction of all-cause mortality and in this review, we analyzed its interactions with human microbiota. In particular, we explored the modulation of the human microbiota, in response to MD adherence, focusing the attention on polyphenols, polyunsaturated fatty acids (PUFA) ω-3 and fiber. Evidences suggest that MD is able to modulate the gut microbiota, increasing its diversity. In fact, a Mediterranean-type dietary pattern is associated with specific gut microbiota characteristics. The available evidence, suggests that gut microbiota of subjects that follow a MD is significantly different from subjects that follow a Western diet model. In fact, the latter show an increased gut permeability, which is responsible for metabolic endotoxemia. For this reason, we can speculate that the gut microbiota of the subjects following a MD is able to prevent the onset of chronic non-communicable degenerative diseases, such as cardiovascular diseases and some types of cancer. However, in order to understand these correlations with dietary patterns, controlled intervention studies on the gut microbiota composition and activity are needed.     

Long-term dietary pattern of fecal donor correlates with butyrate production and markers of protein fermentation during in vitro fecal fermentation

Diet influences gut microbiota composition. Therefore, we hypothesized that diet would impact the extent of dietary fiber utilization and the types of metabolic end-products produced by the microbiota during in vitro fecal fermentation. By obtaining long-term dietary records from fecal donors, we aimed to determine the correlations between dietary intake variables and dietary fiber degradation and short-/branched-chain fatty acid (BCFA) and ammonia production during in vitro fecal fermentation. Eighteen subjects completed 1-year diet history questionnaires and provided fecal samples that were used for in vitro fermentation of a whole wheat substrate. The percentage of dietary fiber fermented was not correlated with nutrient intakes; however, butyrate production was correlated with fecal donor intake of many nutrients of which principal component analysis revealed were mostly contributed by grain-, nut-, and vegetable-based foods. Negative correlations were found for propionate with intake of total carbohydrate, added sugar, and sucrose and for ammonia and BCFA production with intake of unsaturated fats. Thus, our analysis did not support our first hypothesis: the percentage of dietary fiber fermented during in vitro fermentation was not correlated with dietary records. However, production of butyrate; BCFA; ammonia; and, to a lesser extent, propionate was correlated with the diet records of fecal donors, thus supporting our second hypothesis. These results suggest that diets high in plant-based foods and high in unsaturated fats are associated with microbial metabolism that is consistent with host health.