Fiber and Prebiotics: Mechanisms and Health Benefits

The health benefits of dietary fiber have long been appreciated. Higher intakes of dietary fiber are linked to less cardiovascular disease and fiber plays a role in gut health, with many effective laxatives actually isolated fiber sources. Higher intakes of fiber are linked to lower body weights. Only polysaccharides were included in dietary fiber originally, but more recent definitions have included oligosaccharides as dietary fiber, not based on their chemical measurement as dietary fiber by the accepted total dietary fiber (TDF) method, but on their physiological effects. Inulin, fructo-oligosaccharides, and other oligosaccharides are included as fiber in food labels in the US. Additionally, oligosaccharides are the best known “prebiotics”, “a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-bring and health.” To date, all known and suspected prebiotics are carbohydrate compounds, primarily oligosaccharides, known to resist digestion in the human small intestine and reach the colon where they are fermented by the gut microflora. Studies have provided evidence that inulin and oligofructose (OF), lactulose, and resistant starch (RS) meet all aspects of the definition, including the stimulation of Bifidobacterium, a beneficial bacterial genus. Other isolated carbohydrates and carbohydrate-containing foods, including galactooligosaccharides (GOS), transgalactooligosaccharides (TOS), polydextrose, wheat dextrin, acacia gum, psyllium, banana, whole grain wheat, and whole grain corn also have prebiotic effects.     

Intestinal Microbiota-Derived Short Chain Fatty Acids in Host Health and Disease

Intestinal microbiota has its role as an important component of human physiology. It produces metabolites that module key functions to establish a symbiotic crosstalk with their host. Among them, short chain fatty acids (SCFAs), produced by intestinal bacteria during the fermentation of partially and non-digestible polysaccharides, play key roles in regulating colon physiology and changing intestinal environment. Recent research has found that SCFAs not only influence the signal transduction pathway in the gut, but they also reach tissues and organs outside of the gut, through their circulation in the blood. Growing evidence highlights the importance of SCFAs level in influencing health maintenance and disease development. SCFAs are probably involved in the management of host health in a complicated (positive or negative) way. Here, we review the current understanding of SCFAs effects on host physiology and discuss the potential prevention and therapeutics of SCFAs in a variety of disorders. It provides a systematic theoretical basis for the study of mechanisms and precise intake level of SCFAs to promote human health.     

Prebiotics,Fermentable Dietary Fiber,and Health Claims

Since the 1970s, the positive effects of dietary fiber on health have increasingly been recognized. The collective term “dietary fiber” groups structures that have different physiologic effects. Since 1995, some dietary fibers have been denoted as prebiotics, implying a beneficial physiologic effect related to increasing numbers or activity of the gastrointestinal microbiota. Given the complex composition of the microbiota, the demonstration of such beneficial effects is difficult. In contrast, an exploration of the metabolites of dietary fiber formed as a result of its fermentation in the colon offers better perspectives for providing mechanistic links between fiber intake and health benefits. Positive outcomes of such studies hold the promise that claims describing specific health benefits can be granted. This would help bridge the “fiber gap”—that is, the considerable difference between recommended and actual fiber intakes by the average consumer.     

Effects of Anthocyanin on Intestinal Health: A Systematic Review

Intestinal health relies on the association between the mucosal immune system, intestinal barrier and gut microbiota. Bioactive components that affect the gut microbiota composition, epithelial physical barrier and intestinal morphology were previously studied. The current systematic review evaluated evidence of anthocyanin effects and the ability to improve gut microbiota composition, their metabolites and parameters of the physical barrier; this was conducted in order to answer the question: “Does food source or extract of anthocyanin promote changes on intestinal parameters?”. The data analysis was conducted following the PRISMA guidelines with the search performed at PubMed, Cochrane and Scopus databases for experimental studies, and the risk of bias was assessed by the SYRCLE tool. Twenty-seven studies performed in animal models were included, and evaluated for limitations in heterogeneity, methodologies, absence of information regarding allocation process and investigators’ blinding. The data were analyzed, and the anthocyanin supplementation demonstrated positive effects on intestinal health. The main results identified were an increase of Bacteroidetes and a decrease of Firmicutes, an increase of short chain fatty acids production, a decrease of intestinal pH and intestinal permeability, an increase of the number of goblet cells and tight junction proteins and villi improvement in length or height. Thus, the anthocyanin supplementation has a potential effect to improve the intestinal health. PROSPERO (CRD42020204835).     

直肠菌群对两种不溶性膳食纤维的体外发酵

目的探究不溶性膳食纤维在肠道中被发酵利用的规律。方法以直肠菌群为研究对象,以去淀粉麦麸和甘蔗渣分别作为底物,在厌氧条件下进行体外发酵,分别在发酵0、4、8、12和24h取样,测pH、运用选择性平板计数、气相色谱测短链脂肪酸含量。结果以去淀粉麦麸和甘蔗渣为底物的发酵培养基在发酵24h后,pH分别降到了5.35和5.43;双歧杆菌属、乳杆菌属、肠球菌属、肠杆菌属、拟杆菌属以及总厌氧菌的数量在两种底物的培养条件下不同的时间段数量变化均不显著;去淀粉麦麸和甘蔗渣两种底物均能被肠道菌群利用产生短链脂肪酸,其中在发酵24h后丙酸含量最多,且分别为0.58和0.56mg/ml;乳酸在发酵过程中被积累并能被一些肠道菌利用而消耗减少。结论不溶性膳食纤维能被肠道菌群利用,并且在发酵过程中可能有不同菌属的生长演替。     

The Effect of Wheat Bran Particle Size on Laxation and Colonic Fermentation

Objective: Due to perceived inferior fecal bulking ability, finely ground wheat bran is not recommended for treatment of colonic disorders, despite possible short chain fatty acid generation with potential benefits for colonic mucosal health. We therefore tested the effects of very fine particle size wheat bran on colonic function.

Methods: Two studies, each with three phases, were undertaken in healthy subjects in a randomized crossover design. In one study (metabolic, n=23) subjects took three diets containing either an additional 19 g/d dietary fiber with mean particle size (MPS) 50μm or 758μm in bread or a control low fiber bread. In the other study where the supplement was provided as a breakfast cereal (ad libitum, n=24) the respective wheat bran MPS were 692μm and 1158μm and the control was low fiber. Fecal collections were obtained during the last week of each diet. In the metabolic study, fecal short chain fatty acids were measured and 12-hour breath gas collections obtained.

Results: In both studies, wheat bran supplements significantly increased fecal bulk compared to the control (p<0.004), with no significant differences between brans of different particle size and no differences in fecal water content. However, higher fecal butyrate concentrations (p<0.007), butyrate output and breath CH₄ levels (p=0.025) were seen on the low MPS wheat bran compared to the other two treatments, suggesting increased bacterial fermentation.

Conclusions: Fine MPS wheat bran is an effective fecal bulking agent and may have added advantages if increased butyrate concentrations promote colonic mucosal integrity.     

Role of Short Chain Fatty Acids in Epilepsy and Potential Benefits of Probiotics and Prebiotics: Targeting “Health” of Epileptic Patients

The WHO’s definition of health transcends the mere absence of disease, emphasizing physical, mental, and social well-being. As this perspective is being increasingly applied to the management of chronic diseases, research on gut microbiota (GM) is surging, with a focus on its potential for persistent and noninvasive dietary therapeutics. In patients with epilepsy (PWE), a chronic lack of seizure control along with often neglected psychiatric comorbidities greatly disrupt the quality of life. Evidence shows that GM-derived short chain fatty acids (SCFAs) may impact seizure susceptibility through modulating (1) excitatory/inhibitory neurotransmitters, (2) oxidative stress and neuroinflammation, and (3) psychosocial stress. These functions are also connected to shared pathologies of epilepsy and its two most common psychiatric consequences: depression and anxiety. As the enhancement of SCFA production is enabled through direct administration, as well as probiotics and prebiotics, related dietary treatments may exert antiseizure effects. This paper explores the potential roles of SCFAs in the context of seizure control and its mental comorbidities, while analyzing existing studies on the effects of pro/prebiotics on epilepsy. Based on currently available data, this study aims to interpret the role of SCFAs in epileptic treatment, extending beyond the absence of seizures to target the health of PWE.     

Colonic fermentation of some breads and its implication for energy availability in man

Five breads (100% wholemeal wheat (Wheat), 75% bulgar: 25% wheat flour (Bulg1), 50% bulgar: 50% wheat flour (Bulg2), 100% rye (Rye), and 100% pumpernickel (Pump)) were substituted isocalorically for white bread (White) and fed to a healthy ileostomate for three days and the ileal effluent was collected and analysed. Small intestinal apparent metabolizable energy (ME_a) absorption, determined using the Atwater energy system [(crude protein×4.0 Kcal/g)+(extractable fat×9.0 Kcal/g)+(total carbohydrate×4.0 Kcal/g)], decreased for the five breads from 92.7% for white to 88.2% for Pump. The collected ileal effluent was then fermented in vitro with mixed human microflora for 24h and short chain fatty acid (SCFA) production was measured (mmol SCFA/g ileal organic matter) and the available energy (AE) potentially absorbed as SCFA was predicted. It was estimated that the whole grain breads would increase the number of calories being absorbed as SCFA by 20% to 70% relative to white bread. The net metabolizable energy (NME), the sum of ME_a and the AE, available to an individual with an intact colon was estimated to be 96% of the caloric intake determined using the Atwater energy system. However, there was a dramatic shift in energy absorption from the small intestine to the colon with 3.7% of the NME being absorbed as SCFA when white bread was consumed versus 6.3% from pumpernickel.     

Lactobacillus reuteri CCFM8631 Alleviates Hypercholesterolaemia Caused by the Paigen Atherogenic Diet by Regulating the Gut Microbiota

Cardiovascular disease has one of the highest global incidences and mortality rates. Atherosclerosis is the main cause of cardiovascular disease, and hypercholesterolaemia and hyperlipidaemia are the main risk factors for the development of atherosclerosis. Decreasing serum cholesterol and triglyceride concentrations is considered to be an effective strategy to prevent atherosclerotic cardiovascular disease. Previous studies have shown that many diseases are related to gut microbiota dysbiosis. The positive regulation of the gut microbiota by probiotics may prevent or treat certain diseases. In this study, Lactobacillus reuteri CCFM8631 treatment was shown to decrease plasma total cholesterol (TC), low-density lipoprotein–cholesterol, aspartate transaminase, alanine transaminase and trimethylamine N-oxide concentrations, decrease liver TC and malondialdehyde concentrations and recover liver superoxide dismutase concentrations in mice fed a Paigen atherogenic diet. In addition, L. reuteri increased the faecal short-chain fatty acid content (acetate, propionate and butyrate), which was accompanied by an increase in the relative abundance of faecal Deferribacteres, Lachnospiraceae NK4A136 group, Lactobacillus and Dubosiella; a decrease in the relative abundance of Erysipelatoclostridium and Romboutsia and the activation of butanoate and vitamin B6 metabolism, leading to the alleviation of hypercholesterolaemia.     

In vitro fermentation characteristics of a mixture of Raftilose and guar gum by human faecal bacteria

Summary Background The therapeutic effects of indigestible carbohydrates in the human colon are well known. Most fermentation studies have examined only single carbohydrates. Considering the idiosyncratic actions of individual carbohydrates and the dose required, it is unlikely that any one carbohydrate will provide ideal physiological actions without having some undesirable effects. Little is known of how mixing non–digestible carbohydrates affects their fermentation. This necessitates fermentation studies using different carbohydrates in mixtures. Aim of the study The aim of this study was to test the effect of mixing Raftilose™ (R) and guar gum (G) on short chain fatty acid (SCFA) production in in vitro cultures of human faecal bacteria. Method The fermentation of the individual carbohydrates (10 mg/ml) was compared with that of a 50:50 mixture in anaerobic in vitro cultures of human faeces. Results Cultures of R/G mixtures produced significantly more n–butyrate than 100 mg G alone at 8 and 24 hours (p < 0.02). There was no significant difference in the production of n–butyrate between cultures of 100 mg R and the R/G mixture at 8 and 24 hours. R (100 mg) produced a propionic/butyric (p/b) acid ratio of 1.18 compared with 3.88 for 100 mg G, whereas R/G mixture produced a p/b ratio of 2.01. Conclusion The fermentation of R/G mixture was different compared with 100 mg of R or G alone. There was no loss of n–butyrate in the culture containing R/G (50 mg of each) mixture compared with the 100 mg R culture.     

The Effects of High Fiber Rye,Compared to Refined Wheat,on Gut Microbiota Composition,Plasma Short Chain Fatty Acids,and Implications for Weight Loss and Metabolic Risk Factors (the RyeWeight Study)

Consumption of whole grain and cereal fiber have been inversely associated with body weight and obesity measures in observational studies but data from large, long-term randomized interventions are scarce. Among the cereals, rye has the highest fiber content and high rye consumption has been linked to increased production of gut fermentation products, as well as reduced risks of obesity and metabolic disease. The effects on body weight and metabolic risk factors may partly be mediated through gut microbiota and/or their fermentation products. We used data from a randomized controlled weight loss trial where participants were randomized to a hypocaloric diet rich in either high fiber rye foods or refined wheat foods for 12 weeks to investigate the effects of the intervention on gut microbiota composition and plasma short chain fatty acids, as well as the potential association with weight loss and metabolic risk markers. Rye, compared to wheat, induced some changes in gut microbiota composition, including increased abundance of the butyrate producing Agathobacter and reduced abundance of [Ruminococcus] torques group, which may be related to reductions in low grade inflammation caused by the intervention. Plasma butyrate increased in the rye group. In conclusion, intervention with high fiber rye foods induced some changes in gut microbiota composition and plasma short chain fatty acid concentration, which were associated with improvements in metabolic risk markers as a result of the intervention.     

Fermentation Profiles of Wheat Dextrin,Inulin and Partially Hydrolyzed Guar Gum Using an in Vitro Digestion Pretreatment and in Vitro Batch Fermentation System Model

This study investigated the fermentation and microbiota profiles of three fibers, wheat dextrin (WD), partially hydrolyzed guar gum (PHGG), and inulin, since little is known about the effects of WD and PHGG on gut microbiota. A treatment of salivary amylase, pepsin, and pancreatin was used to better physiologic digestion. Fibers (0.5 g) were fermented in triplicate including a control group without fiber for 0, 4, 8, 12, and 24 h. Analysis of pH, gas volume, hydrogen and methane gases, and short chain fatty acid (SCFA) concentrations were completed at each time point. Quantitative polymerase chain reaction (qPCR) was used to measure Bifidobacteria and Lactobacillus CFUs at 24 h. WD produced the least gas during fermentation at 8, 12, and 24 h (P < 0.0001), while inulin produced the most by 8 h (P < 0.0001). Each fiber reached its lowest pH value at different time points with inulin at 8 h (mean ± SE) (5.94 ± 0.03), PHGG at 12 h (5.98 ± 0.01), and WD at 24 h (6.17 ± 0.03). All fibers had higher total SCFA concentrations compared to the negative control (P < 0.05) at 24 h. At 24 h, inulin produced significantly (P = 0.0016) more butyrate than WD with PHGG being similar to both. An exploratory microbial analysis (log₁₀ CFU/µL) showed WD had CFU for Bifidobacteria (6.12) and Lactobacillus (7.15) compared with the control (4.92 and 6.35, respectively). Rate of gas production is influenced by fiber source and may affect tolerance in vivo. Exploratory microbiota data hint at high levels of Bifidobacteria for WD, but require more robust investigation to corroborate these findings.     

Health effects of resistant starch

The merits of a fibre‐rich diet are well documented. Resistant starch (RS) is a form of starch that resists digestion in the small intestine and, as such, is classified as a type of dietary fibre. RS can be categorised as one of five types (RS1–5), some of which occur naturally in foods such as bananas, potatoes, grains and legumes and some of which are produced or modified commercially, and incorporated into food products. This review describes human evidence on the health effects of RS consumption, with the aim of identifying any benefits of RS‐rich foods and RS as a functional ingredient. The reduced glycaemic response consistently reported with RS consumption, when compared with digestible carbohydrate, has resulted in an approved European Union health claim. Thus, RS‐rich foods may be particularly useful for managing diabetes. There appears to be little impact of RS on other metabolic markers, such as blood pressure and plasma lipids, though data are comparatively limited. Promising results on markers of gut health suggest that further research may lead to the classification of RS as a prebiotic. Microbial fermentation of RS in the large intestine to produce short‐chain fatty acids likely underpins some of its biological effects, including increasing satiety. However, effects on appetite have not resulted in notable changes in bodyweight after long‐term consumption. Emerging research suggests potential for RS as an ingredient in oral rehydration solutions and in the treatment of chronic kidney disease. Overall, RS possesses positive properties as a healthy food component.     

Phosphate,Microbiota and CKD

Phosphate is a key uremic toxin associated with adverse outcomes. As chronic kidney disease (CKD) progresses, the kidney capacity to excrete excess dietary phosphate decreases, triggering compensatory endocrine responses that drive CKD-mineral and bone disorder (CKD-MBD). Eventually, hyperphosphatemia develops, and low phosphate diet and phosphate binders are prescribed. Recent data have identified a potential role of the gut microbiota in mineral bone disorders. Thus, parathyroid hormone (PTH) only caused bone loss in mice whose microbiota was enriched in the Th17 cell-inducing taxa segmented filamentous bacteria. Furthermore, the microbiota was required for PTH to stimulate bone formation and increase bone mass, and this was dependent on bacterial production of the short-chain fatty acid butyrate. We review current knowledge on the relationship between phosphate, microbiota and CKD-MBD. Topics include microbial bioactive compounds of special interest in CKD, the impact of dietary phosphate and phosphate binders on the gut microbiota, the modulation of CKD-MBD by the microbiota and the potential therapeutic use of microbiota to treat CKD-MBD through the clinical translation of concepts from other fields of science such as the optimization of phosphorus utilization and the use of phosphate-accumulating organisms.     

直肠菌群对两种植物胶的体外发酵特性研究

目的探讨植物胶被肠道菌群发酵利用的规律。方法本研究分别以瓜尔豆胶和果胶为唯一碳源,对直肠菌群进行体外发酵,分别在不同时间取样,测pH、运用选择性平板计数、气相色谱测短链脂肪酸含量。结果两种培养基在肠道菌群发酵过程中,发酵液的pH值呈逐渐下降趋势;除乳杆菌属外,其它各类菌在两种碳源的培养条件下均有较明显的下降,尤其是拟杆菌的数量在发酵中后期急剧减少,但总厌氧菌数较稳定。两种碳源均能被肠道菌群利用产生短链脂肪酸,其中瓜尔豆胶产异丁酸量最大,其次为丙酸,丁酸的产量最少,乳酸在发酵过程中短暂积累后被迅速利用而消耗;果胶产丙酸的量最大,乙酸次之,丁酸的产量最少,乳酸虽然也有一个短暂蓄积,但量非常少而且8h后检测不到乳酸。结论食物中所含植物胶能被肠道菌群利用,并且在发酵过程中肯定有不同菌属的生长演替,但两种植物胶都不利于拟杆菌属的生长。     

A Novel Sprouted Oat Fermented Beverage: Evaluation of Safety and Health Benefits for Celiac Individuals

The safety and health effects for celiac people of a novel beverage (SOFB) developed from sprouted oat flour by fermentation with Lactobacillus plantarum was explored. In vitro reactivity against anti-gliadin antibodies (AGA) and antioxidant/anti-inflammatory potential of SOFB in RAW 264.7 macrophages and Caco-2 cells were evaluated. Immunoreactivity against AGA and antioxidant activity were not detected in SOFB, but it exhibited significant anti-inflammatory activity. The tolerability and impact of SOFB consumption for 6 months on nutritional status and intestinal microbiota composition were investigated in 10 celiac adults (five treated and five control). SOFB consumption did not adversely affect duodenal mucosa nor the total IgA or anti-tissue transglutaminase antibody (IgA-tTG) levels in celiac participants, but it significantly decreased total cholesterol levels at all sampling times and folic acid levels at the end of the study compared to the placebo beverage. SOFB administration also shifted gut microbiota, leading to a higher relative abundance of some beneficial bacteria including the genera Subdoligranulum, Ruminococcus and Lactobacillus in the SOFB group. This study provides supporting evidence of the safety of health benefits of a novel functional beverage produced from sprouted oat.     

Colonic Medium-Chain Fatty Acids Act as a Source of Energy and for Colon Maintenance but Are Not Utilized to Acylate Ghrelin

The capacity of microbiota to produce medium-chain fatty acids (MCFA) and related consequences for the gastrointestinal (GI) tract have never been reported before. We verified the impact of nutrition-related factors on fatty acid (FAs) production and found that caloric restriction decreased levels of most of MCFAs in the mouse cecum, whereas overnight fasting reduced the levels of acetate and butyrate but increased propionate and laurate. A diet high in soluble fibre boosted the production of short-chain fatty acids (SCFA) and caproate whereas a high-cellulose diet did not have an effect or decreased the levels of some of the FAs. Rectal infusion of caprylate resulted in its rapid metabolism for energy production. Repeated 10-day MCFA infusion impacted epididymal white adipose tissue (eWAT) weight and lipid accumulation. Repeated infusion of caprylate rectally tended to increase the concentration of active ghrelin in mice plasma; however, this increase was not statistically significant. In Caco-2 cells, caprylate increased the expression of Fabp2, Pdk4, Tlr3, and Gpr40 genes as well as counteracted TNFα-triggered downregulation of Pparγ, Occludin, and Zonulin mRNA expression. In conclusion, we show that colonic MCFAs can be rapidly utilized as a source of energy or stored as a lipid supply. Further, locally produced caprylate may impact metabolism and inflammatory parameters in the colon.