Wheat Dextrin, Psyllium, and Inulin Produce Distinct Fermentation Patterns, Gas Volumes, and Short-Chain Fatty Acid ProfilesIn Vitro

Dietary fibre definition revisited - The case of low molecular weight carbohydrates

Low molecular weight (LMW) non-digestible carbohydrates (namely, oligosaccharides and inulin) are accepted as dietary fibre in many countries worldwide. The inclusion of oligosaccharides as dietary fibre was made optional within the Codex Alimentarius definition in 2009, which has caused great controversy. Inulin is accepted as dietary fibre by default, due to being a non-digestible carbohydrate polymer. Oligosaccharides and inulin occur naturally in numerous foods and are frequently incorporated into commonly consumed food products for a variety of purposes, such as to increase dietary fibre content. LMW non-digestible carbohydrates, due to their rapid fermentation in the proximal colon, may cause deleterious effects in individuals with functional bowel disorders (FBDs) and, as such, are excluded on the low FODMAP (fermentable oligosaccharides, disaccharides, and polyols) diet and similar protocols. Their addition to food products as dietary fibre allows the use of associated nutrition/health claims, causing a paradox for those with FBDs, which is further complicated by lack of clarity on food labelling. Therefore, this review aimed to discuss whether the inclusion of LMW non-digestible carbohydrates within the Codex definition of dietary fibre is warranted. This review provides justification for the exclusion of oligosaccharides and inulin from the Codex definition of dietary fibre. LMW non-digestible carbohydrates could, instead, be placed in their own category as prebiotics, recognised for their specific functional properties, or considered food additives, whereby they are not promoted for being beneficial for health. This would preserve the concept of dietary fibre being a universally beneficial dietary component for all individuals.

Current evidence on the therapeutic use of fiber in irritable bowel syndrome

INTRODUCTION

Patients with irritable bowel syndrome (IBS) frequently resort to natural products, or request doctors to prescribe them, to relieve their symptoms, due to the poor efficacy and tolerability of several traditional drugs. Products containing fiber are among the most used and their clinical efficacy is discussed here based on the most recent scientific evidence.

AREAS COVERED

A literature search was carried out to identify the most significant publications in order to deal with the topics of the general characteristics of fibers and the scientific evidence underlying their therapeutic use, the properties of ispaghula husk and the mechanisms by which this product carries out its therapeutic actions.

EXPERT OPINION

The most recent clinical guidelines on the management of IBS consider ispaghula husk, a product containing soluble fiber, as a reasonable first line therapy for IBS patients with symptoms. In contrast, products containing insoluble fibers, particularly wheat bran, do not appear to be useful in treating IBS symptoms. The clinical data on the use of prebiotics in IBS are still inconclusive. However, low daily amounts of fructo-oligosaccharides or β-galacto-oligosaccharides (also known as trans-galacto-oligosaccharides) may be effective in improving IBS symptoms; further trials are needed to definitively establish their clinical usefulness.

Potential Prebiotic and Anti-Obesity Effects of Codium fragile Extract

Polysaccharides from marine algae exhibit beneficial biological activities. In this study, we examined the effect of Codium fragile extract (CFE) on prebiotic and anti-obesity activity through in vitro experiments. CFE increases the growth of specific beneficial microbial populations with concomitant decrease in pathogenic microbes. Further, total phenolic content (TPC), total flavonoid content (TFC), and DPPH radical scavenging activity (DPPH activity) after fermentation with CFE as the carbon source were higher than for glucose as the control. Moreover, CFE inhibited adipocyte differentiation by inducing differentiation-related factors when the induction of 3T3-L1 preadipocytes into adipocytes was induced. Therefore, we suggest that CFE can be used as a prebiotic material with an anti-obesity effect for human health.

Prebiotic Inulin and Sodium Butyrate Attenuate Obesity-Induced Intestinal Barrier Dysfunction by Induction of Antimicrobial Peptides

Defects in the mucosal barrier have been associated with metabolic diseases such as obesity and non-alcoholic fatty liver disease (NAFLD). Mice fed a Western-style diet (WSD) develop obesity and are characterized by a diet-induced intestinal barrier dysfunction, bacterial endotoxin translocation and subsequent liver steatosis. To examine whether inulin or sodium butyrate could improve gut barrier dysfunction, C57BL/6 mice were fed a control diet or a WSD ± fructose supplemented with either 10% inulin or 5% sodium butyrate for 12 weeks respectively. Inulin and sodium butyrate attenuated hepatosteatitis in the WSD-induced obesity mouse model by reducing weight gain, liver weight, plasma and hepatic triglyceride level. Furthermore, supplementation with inulin or sodium butyrate induced expression of Paneth cell α-defensins and matrix metalloproteinase-7 (MMP7), which was impaired by the WSD and particularly the fructose-added WSD. Effects on antimicrobial peptide function in the ileum were accompanied by induction of β-defensin-1 and tight junction genes in the colon resulting in improved intestinal permeability and endotoxemia. Organoid culture of small intestinal crypts revealed that the short chain fatty acids (SCFA) butyrate, propionate and acetate, fermentation products of inulin, induce Paneth cell α-defensin expression in vitro, and that histone deacetylation and STAT3 might play a role in butyrate-mediated induction of α-defensins. In summary, inulin and sodium butyrate attenuate diet-induced barrier dysfunction and induce expression of Paneth cell antimicrobials. The administration of prebiotic fiber or sodium butyrate could be an interesting therapeutic approach to improve diet-induced obesity.

Butyrate alleviates PTZ-induced mitochondrial dysfunction, oxidative stress and neuron apoptosis in mice via Keap1/Nrf2/HO-1 pathway

This study aims to evaluate the neuroprotective effect of sodium butyrate against the pentylenetetrazol (PTZ)-induced kindling epilepsy. Sodium butyrate (SB) (5, 10 and 20 mg/kg) and sodium valproate for 40 days and PTZ (37 mg/kg) injection every day were conducted for Kunming mice, to investigate seizure intensity and latency, oxidative stress parameters, mitochondrial structure and function, histopathology, and Keap1/Nrf2/HO-1 expressions. It is shown that seizure latency was effectively increased and the intensity of seizures decreased by treatment with sodium butyrate. It was also found to reverse the structural disruption of the mitochondria, reduce the ROS level and improve the levels of NAD + and ATP in the brains of epileptic mice. Furthermore, pretreatment with SB led to an increase in antioxidant enzyme activity (CAT, SOD and GSH-PX) in the brain as well as conferred a neuroprotective effect against neuron loss and apoptosis. The activation of Keap1/Nrf2/HO-1 signals was also identified, in which the antiepileptic effect of SB may be partially due to its anti-mitochondrial injury and neuroprotective activities. Accordingly, the results of a series of functional tests indicate a significant improvement of neurological function following SB treatment. In a mouse model of seizures, brain injury and neurological deficits can be attenuated by treatment with butyrate through the activation of Nrf2 pathway and the improvement of mitochondrial function.

A Novel Non-Digestible, Carrot-Derived Polysaccharide (cRG-I) Selectively Modulates the Human Gut Microbiota while Promoting Gut Barrier Integrity: An Integrated in Vitro Approach

Modulation of the gut microbiome as a means to improve human health has recently gained increasing interest. In this study, it was investigated whether cRG-I, a carrot-derived pectic polysaccharide, enriched in rhamnogalacturonan-I (RG-I) classifies as a potential prebiotic ingredient using novel in vitro models. First, digestion methods involving α-amylase/brush border enzymes demonstrated the non-digestibility of cRG-I by host-derived enzymes versus digestible (starch/maltose) and non-digestible controls (inulin). Then, a recently developed short-term (48 h) colonic incubation strategy was applied and revealed that cRG-I fermentation increased levels of health-promoting short-chain fatty acids (SCFA; mainly acetate and propionate) and lactate comparable but not identical to the reference prebiotic inulin. Upon upgrading this fermentation model by inclusion of a simulated mucosal environment while applying quantitative 16S-targeted Illumina sequencing, cRG-I was additionally shown to specifically stimulate operational taxonomic units (OTUs) related to health-associated species such as Bifidobacterium longum, Bifidobacterium adolescentis, Bacteroides dorei, Bacteroides ovatus, Roseburia hominis, Faecalibacterium prausnitzii, and Eubacterium hallii. Finally, in a novel model to assess host–microbe interactions (Caco-2/peripheral blood mononuclear cells (PBMC) co-culture) fermented cRG-I increased barrier integrity while decreasing markers for inflammation. In conclusion, by using novel in vitro models, cRG-I was identified as a promising prebiotic candidate to proceed to clinical studies.

Resistant dextrin improves high-fat-high-fructose diet induced insulin resistance

Background

Insulin resistance is an important defect associated with obesity and type 2 diabetes mellitus. Many studies have been reported that dietary fiber exerts beneficial metabolic effects. Resistant dextrin is a soluble fiber. The aim of this study was to investigate the effects of resistant dextrin on high-fat-high-fructose diet induced obese mice and to explore the underlying mechanisms.

Methods

Seventeen 4-week-old male C57BL/6 J mice were fed a normal diet (ND) or HFHFD for 22 weeks, and were gavaged with resistant dextrin (5 g/kg) for 10 weeks. Glucose tolerance test (GTT) and insulin tolerance test (ITT) were performed, serum fasting insulin (FINS) and serum biochemical parameters were determined, the contents of triglyceride (TG) and total cholesterol (TC) in liver tissues were determined by enzymatic method. The pathological changes in liver were detected by HE staining. Real time PCR and Western blot were used to detect the expression of insulin signaling pathway and the fatty acid β oxidation pathway related genes and proteins respectively. The gut microbiota were analyzed via 16 s rRNA sequencing.

Results

Resistant dextrin significantly decreased serum FINS, improved serum lipid profiles, reduced the contents of liver TG and TC. The insulin signaling pathway and the fatty acid β oxidation pathway were promoted. The abundance of metabolically beneficial bacteria such as Prevotella and Akkermansia in the intestinal flora of the resistant dextrin group were increased.

Conclusions

Resistant dextrin can significantly ameliorate liver insulin resistance, improve serum lipid levels, as well as reduce hepatic lipid deposition. The modulation of gut microbiota might be responsible for the beneficial effects of resistant dextrin.

Prebiotics from Seaweeds: An Ocean of Opportunity?

Seaweeds are an underexploited and potentially sustainable crop which offer a rich source of bioactive compounds, including novel complex polysaccharides, polyphenols, fatty acids, and carotenoids. The purported efficacies of these phytochemicals have led to potential functional food and nutraceutical applications which aim to protect against cardiometabolic and inflammatory risk factors associated with non-communicable diseases, such as obesity, type 2 diabetes, metabolic syndrome, cardiovascular disease, inflammatory bowel disease, and some cancers. Concurrent understanding that perturbations of gut microbial composition and metabolic function manifest throughout health and disease has led to dietary strategies, such as prebiotics, which exploit the diet-host-microbe paradigm to modulate the gut microbiota, such that host health is maintained or improved. The prebiotic definition was recently updated to "a substrate that is selectively utilised by host microorganisms conferring a health benefit", which, given that previous discussion regarding seaweed prebiotics has focused upon saccharolytic fermentation, an opportunity is presented to explore how non-complex polysaccharide components from seaweeds may be metabolised by host microbial populations to benefit host health. Thus, this review provides an innovative approach to consider how the gut microbiota may utilise seaweed phytochemicals, such as polyphenols, polyunsaturated fatty acids, and carotenoids, and provides an updated discussion regarding the catabolism of seaweed-derived complex polysaccharides with potential prebiotic activity. Additional in vitro screening studies and in vivo animal studies are needed to identify potential prebiotics from seaweeds, alongside untargeted metabolomics to decipher microbial-derived metabolites from seaweeds. Furthermore, controlled human intervention studies with health-related end points to elucidate prebiotic efficacy are required.

The prebiotic inulin improves substrate metabolism and promotes short-chain fatty acid production in overweight to obese men

BACKGROUND AND AIMS

Human gut microbiota play an important role in maintaining human health. Dietary fibers, i.e. prebiotics, are fermented by human gut microbiota into the short-chain fatty acids (SCFAs) acetate, propionate, and butyrate. SCFAs promote fat oxidation and improve metabolic health. Therefore, the prebiotic inulin might be an effective dietary strategy to improve human metabolism. We aimed to investigate the acute metabolic effects of ingesting inulin compared with digestible carbohydrates and to trace inulin-derived SCFAs using stable isotope tracer methodology.

METHODS

In a double-blind, randomized, placebo-controlled crossover design, 14 healthy, overweight to obese men consumed a high-fat milkshake containing A) 24 g inulin of which 0.5 g was U-¹³C-inulin (INU) or B) 24 g maltodextrin placebo (PLA), with a wash-out period of at least five days. Fat oxidation was measured via an open-circuit ventilated hood and blood samples were collected up to 7 h after ingestion. Plasma, breath, and fecal samples were collected, and appetite and satiety scores were assessed.

RESULTS

Fat oxidation increased in the early postprandial phase (0-3 h), and both plasma glucose and insulin were lower after INU ingestion compared with PLA (all P < 0.05). Plasma free fatty acids were higher in the early, and lower in the late postprandial period after INU ingestion. Inulin was fermented into SCFAs as indicated by higher plasma acetate concentrations after INU compared with PLA (P < 0.05). In addition, we found continuous increases in plasma ¹³C-SCFA enrichments (P < 0.05 from t = 120 onwards) and breath ¹³CO₂ enrichments after INU intake. There were no effects on plasma triglycerides, free glycerol, satiety hormones GLP-1 and PYY, and appetite and satiety scores.

CONCLUSIONS

Ingestion of the prebiotic inulin improves fat oxidation and promotes SCFA production in overweight to obese men. Overall, replacing digestible carbohydrates with the fermentable inulin may favor human substrate metabolism.

CLINICAL TRIAL REGISTRY

The trial was registered at clinicaltrials.gov under number NCT02009670.

Fermentability of Novel Type-4 Resistant Starches in In Vitro System

Resistant starches are non-digestible starches that are fermented in the colon by microbiota. These carbohydrates are prebiotic and can be beneficial to consumer health. Many types of resistant starch exist with varying physical properties that may result in differences in fermentability. The objective of this research project was to compare potential prebiotic effects and fermentability of four novel resistant starches using an in vitro fermentation system and measuring changes in total gas production, pH, and formation of SCFAs (short chain fatty acids). Fecal donations were collected from seven healthy volunteers. Four novel resistant starches, modified potato starch (MPS), modified tapioca starch (MTS), and modified maize starches (MMS-1 and MMS-2), were analyzed and compared to polydextrose and short chain fructooligosaccharides (FOS) as controls. After twenty-four hours of fermentation, MPS and MTS responded similarly in gas production (74 mL; 70.6 mL respectively), pH (5.93; 5.93 respectively), and SCFA production (Acetate: 115; 124, Propionate: 21; 26, Butyrate: 29; 31 μmol/mL respectively). While MMS-1 had similar gas production and individual SCFA production, the pH was significantly higher (6.06). The fermentation of MMS-2 produced the least amount of gas (22 mL), with a higher pH (6.34), and lower acetate production (78.4 μmol/mL). All analyzed compounds were fermentable and promoted the formation of beneficial SCFAs.

Prebiotic Dietary Fiber and Gut Health: Comparing the in Vitro Fermentations of Beta-Glucan, Inulin and Xylooligosaccharide

Prebiotic dietary fiber supplements are commonly consumed to help meet fiber recommendations and improve gastrointestinal health by stimulating beneficial bacteria and the production of short-chain fatty acids (SCFAs), molecules beneficial to host health. The objective of this research project was to compare potential prebiotic effects and fermentability of five commonly consumed fibers using an in vitro fermentation system measuring changes in fecal microbiota, total gas production and formation of common SCFAs. Fecal donations were collected from three healthy volunteers. Materials analyzed included: pure beta-glucan, Oatwell (commercially available oat-bran containing 22% oat β-glucan), xylooligosaccharides (XOS), WholeFiber (dried chicory root containing inulin, pectin, and hemi/celluloses), and pure inulin. Oatwell had the highest production of propionate at 12 h (4.76 μmol/mL) compared to inulin, WholeFiber and XOS samples (p < 0.03). Oatwell's effect was similar to those of the pure beta-glucan samples, both samples promoted the highest mean propionate production at 24 h. XOS resulted in a significant increase in the genus Bifidobacterium after 24 h of fermentation (0 h:0.67 OTUs (operational taxonomic unit); 24 h:5.22 OTUs; p = 0.038). Inulin and WholeFiber increased the beneficial genus Collinsella, consistent with findings in clinical studies. All analyzed compounds were fermentable and promoted the formation of beneficial SCFAs.

Biomarkers for nutrient intake with focus on alternative sampling techniques

Biomarkers of nutrient intake or nutrient status are important objective measures of foods/nutrients as one of the most important environmental factors people are exposed to. It is very difficult to obtain accurate data on individual food intake, and there is a large variation of nutrient composition of foods consumed in a population. Thus, it is difficult to obtain precise measures of exposure to different nutrients and thereby be able to understand the relationship between diet, health, and disease. This is the background for investing considerable resources in studying biomarkers of nutrients believed to be important in our foods. Modern technology with high sensitivity and specificity concerning many nutrient biomarkers has allowed an interesting development with analyses of very small amounts of blood or tissue material. In combination with non-professional collection of blood by finger-pricking and collection on filters or sticks, this may make collection of samples and analyses of biomarkers much more available for scientists as well as health professionals and even lay people in particular in relation to the marked trend of self-monitoring of body functions linked to mobile phone technology. Assuming standard operating procedures are used for collection, drying, transport, extraction, and analysis of samples, it turns out that many analytes of nutritional interest can be measured like metabolites, drugs, lipids, vitamins, minerals, and many types of peptides and proteins. The advantage of this alternative sampling technology is that non-professionals can collect, dry, and mail the samples; the samples can often be stored under room temperature in a dry atmosphere, requiring small amounts of blood. Another promising area is the potential relation between the microbiome and biomarkers that may be measured in feces as well as in blood.

Beneficial effects of soy milk and fiber on high cholesterol diet-induced alteration of gut microbiota and inflammatory gene expression in rats

We sought to evaluate whether a soy milk and fiber mixture could improve high cholesterol diet-induced changes in gut microbiota and inflammation. Sprague-Dawley rats were administered four different diets: CTRL (AIN76A diet), CHOL (AIN76A with 1% (w/w) cholesterol), SOY (CHOL diet, 20% of which was substituted with freeze-dried soy milk), or S.FIBER (SOY diet with 1.2% (w/w) psyllium, 6.2% (w/w) resistant maltodextrin, and 6.2% (w/w) chicory powder). A lipid profile and gene expression analysis demonstrated that SOY and S.FIBER improved the serum HDL-cholesterol and colonic expression levels of genes in tight junction (ZO-1 and occludin) and inflammation-related (IL-1β, IL-10, and Foxp3) proteins. S.FIBER lowered the serum MCP-1 concentration as well. A gut microbial analysis revealed that CHOL increased the ratio of Firmicutes to Bacteroidetes (F/B ratio). SOY increased the F/B ratio due to an increased proportion of Lactobacillus spp. S.FIBER greatly decreased the F/B ratio. Allobaculum spp. and Parabacteroides spp. exhibited a negative correlation with colonic expression of anti-inflammatory genes such as Foxp3, IL-10, occludin and ZO-1. CHOL increased the relative proportions of Allobaculum spp. and Parabacteroides spp. in the gut, while SOY and S.FIBER decreased these proportions. Diets containing soy milk and fiber mixtures could be beneficial by limiting CHOL-induced colonic inflammation and rescuing CHOL-disturbed gut microbiota.

In vitro fermentation of alginate and its derivatives by human gut microbiota

Alginate (Alg) has a long history as a food ingredient in East Asia. However, the human gut microbes responsible for the degradation of alginate and its derivatives have not been fully understood yet. Here, we report that alginate and the low molecular polymer derivatives of mannuronic acid oligosaccharides (MO) and guluronic acid oligosaccharides (GO) can be completely degraded and utilized at various rates by fecal microbiota obtained from six Chinese individuals. However, the derivative of propylene glycol alginate sodium sulfate (PSS) was not hydrolyzed. The bacteria having a pronounced ability to degrade Alg, MO and GO were isolated from human fecal samples and were identified as Bacteroides ovatus, Bacteroides xylanisolvens, and Bacteroides thetaiotaomicron. Alg, MO and GO can increase the production level of short chain fatty acids (SCFA), but GO generates the highest level of SCFA. Our data suggest that alginate and its derivatives could be degraded by specific bacteria in the human gut, providing the basis for the impacts of alginate and its derivates as special food additives on human health.

Quantification of in Vivo Colonic Short Chain Fatty Acid Production from Inulin

Short chain fatty acids (SCFA), including acetate, propionate, and butyrate, are produced during bacterial fermentation of undigested carbohydrates in the human colon. In this study, we applied a stable-isotope dilution method to quantify the in vivo colonic production of SCFA in healthy humans after consumption of inulin. Twelve healthy subjects performed a test day during which a primed continuous intravenous infusion with [1-¹³C]acetate, [1-¹³C]propionate and [1-¹³C]butyrate (12, 1.2 and 0.6 μmol·kg⁻¹·min⁻¹, respectively) was applied. They consumed 15 g of inulin with a standard breakfast. Breath and blood samples were collected at regular times during the day over a 12 h period. The endogenous rate of appearance of acetate, propionate, and butyrate was 13.3 ± 4.8, 0.27 ± 0.09, and 0.28 ± 0.12 μmol·kg⁻¹·min⁻¹, respectively. Colonic inulin fermentation was estimated to be 137 ± 75 mmol acetate, 11 ± 9 mmol propionate, and 20 ± 17 mmol butyrate over 12 h, assuming that 40%, 10%, and 5% of colonic derived acetate, propionate, and butyrate enter the systemic circulation. In conclusion, inulin is mainly fermented into acetate and, to lesser extents, into butyrate and propionate. Stable isotope technology allows quantifying the production of the three main SCFA in vivo and proved to be a practical tool to investigate the extent and pattern of SCFA production.

Towards microbial fermentation metabolites as markers for health benefits of prebiotics

Available evidence on the bioactive, nutritional and putative detrimental properties of gut microbial metabolites has been evaluated to support a more integrated view of how prebiotics might affect host health throughout life. The present literature inventory targeted evidence for the physiological and nutritional effects of metabolites, for example, SCFA, the potential toxicity of other metabolites and attempted to determine normal concentration ranges. Furthermore, the biological relevance of more holistic approaches like faecal water toxicity assays and metabolomics and the limitations of faecal measurements were addressed. Existing literature indicates that protein fermentation metabolites (phenol, p-cresol, indole, ammonia), typically considered as potentially harmful, occur at concentration ranges in the colon such that no toxic effects are expected either locally or following systemic absorption. The endproducts of saccharolytic fermentation, SCFA, may have effects on colonic health, host physiology, immunity, lipid and protein metabolism and appetite control. However, measuring SCFA concentrations in faeces is insufficient to assess the dynamic processes of their nutrikinetics. Existing literature on the usefulness of faecal water toxicity measures as indicators of cancer risk seems limited. In conclusion, at present there is insufficient evidence to use changes in faecal bacterial metabolite concentrations as markers of prebiotic effectiveness. Integration of results from metabolomics and metagenomics holds promise for understanding the health implications of prebiotic microbiome modulation but adequate tools for data integration and interpretation are currently lacking. Similarly, studies measuring metabolite fluxes in different body compartments to provide a more accurate picture of their nutrikinetics are needed.

Evidence-Based Approach to Fiber Supplements and Clinically Meaningful Health Benefits, Part 2: What to Look for and How to Recommend an Effective Fiber Therapy

Dietary fiber that is intrinsic and intact in fiber-rich foods (eg, fruits, vegetables, legumes, whole grains) is widely recognized to have beneficial effects on health when consumed at recommended levels (25 g/d for adult women, 38 g/d for adult men). Most (90%) of the US population does not consume this level of dietary fiber, averaging only 15 g/d. In an attempt to bridge this “fiber gap,” many consumers are turning to fiber supplements, which are typically isolated from a single source. Fiber supplements cannot be presumed to provide the health benefits that are associated with dietary fiber from whole foods. Of the fiber supplements on the market today, only a minority possess the physical characteristics that underlie the mechanisms driving clinically meaningful health benefits. In this 2-part series, the first part (previous issue) described the 4 main characteristics of fiber supplements that drive clinical efficacy (solubility, degree/rate of fermentation, viscosity, and gel formation), the 4 clinically meaningful designations that identify which health benefits are associated with specific fibers, and the gel-dependent mechanisms in the small bowel that drive specific health benefits (eg, cholesterol lowering, improved glycemic control). The second part (current issue) of this 2-part series will focus on the effects of fiber supplements in the large bowel, including the 2 mechanisms by which fiber prevents/relieves constipation (insoluble mechanical irritant and soluble gel-dependent water-holding capacity), the gel-dependent mechanism for attenuating diarrhea and normalizing stool form in irritable bowel syndrome, and the combined large bowel/small bowel fiber effects for weight loss/maintenance. The second part will also discuss how processing for marketed products can attenuate efficacy, why fiber supplements can cause gastrointestinal symptoms, and how to avoid symptoms for better long-term compliance.

Potential anti-obesogenic properties of non-digestible carbohydrates: specific focus on resistant dextrin

Alterations in the composition and metabolic activity of the gut microbiota appear to contribute to the development of obesity and associated metabolic diseases. However, the extent of this relationship remains unknown. Modulating the gut microbiota with non-digestible carbohydrates (NDC) may exert anti-obesogenic effects through various metabolic pathways including changes to appetite regulation, glucose and lipid metabolism and inflammation. The NDC vary in physicochemical structure and this may govern their physical properties and fermentation by specific gut bacterial populations. Much research in this area has focused on established prebiotics, especially fructans (i.e. inulin and fructo-oligosaccharides); however, there is increasing interest in the metabolic effects of other NDC, such as resistant dextrin. Data presented in this review provide evidence from mechanistic and intervention studies that certain fermentable NDC, including resistant dextrin, are able to modulate the gut microbiota and may alter metabolic process associated with obesity, including appetite regulation, energy and lipid metabolism and inflammation. To confirm these effects and elucidate the responsible mechanisms, further well-controlled human intervention studies are required to investigate the impact of NDC on the composition and function of the gut microbiota and at the same time determine concomitant effects on host metabolism and physiology.

Estimation and interpretation of fermentation in the gut: coupling results from a 24 h batch in vitro system with fecal measurements from a human intervention feeding study using fructo-oligosaccharides, inulin, gum acacia, and pea fiber

Gut bacteria ferment fiber at different rates to primarily short chain fatty acids (SCFA) and gas while proteins are metabolized to SCFA, branched chain fatty acids (BCFA), gas, and undesirable metabolites. Large volumes of gas produced in vivo may contribute to bloating and flatulence in an individual. The objectives of this trial were to (1) compare the in vitro fermentation profiles of fructo-oligosaccharides (FOS), inulin, gum acacia, and pea fiber alone or blended using a 24 h batch model and (2) relate these findings to a human study that fed enteral formula fortified with fiber blend (FB) or no fiber (FF). The in vitro fermentation of the fiber blend resulted in a delayed pH decrease and gas and SCFA production compared to the FOS and inulin. Human samples had higher SCFA on FB compared to FF (p = 0.029). BCFA were not different between formulas. By using a blend of fibers, we observed a slower fermentation in vitro but still increased fecal SCFA when fed to human subjects.

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.

Fiber and functional gastrointestinal disorders

Despite years of advising patients to alter their dietary and supplementary fiber intake, the evidence surrounding the use of fiber for functional bowel disease is limited. This paper outlines the organization of fiber types and highlights the importance of assessing the fermentation characteristics of each fiber type when choosing a suitable strategy for patients. Fiber undergoes partial or total fermentation in the distal small bowel and colon leading to the production of short-chain fatty acids and gas, thereby affecting gastrointestinal function and sensation. When fiber is recommended for functional bowel disease, use of a soluble supplement such as ispaghula/psyllium is best supported by the available evidence. Even when used judiciously, fiber can exacerbate abdominal distension, flatulence, constipation, and diarrhea.

Impact of a resistant dextrin on intestinal ecology: how altering the digestive ecosystem with NUTRIOSE®, a soluble fibre with prebiotic properties, may be beneficial for health

OBJECTIVES

The prebiotic potential of NUTRIOSE®--a sugar-free, digestion-resistant dextrin--was evaluated in two randomized, placebo-controlled trials that included 48 and 40 healthy volunteers, respectively.

METHODS

In study 1, the effect on colonic bacteria of NUTRIOSE® 10, 15 or 20 g/day administered for 14 days was examined; in study 2, gut microbial changes in response to NUTRIOSE® 8 g/day for 14 days were monitored using real-time polymerase chain reaction analysis.

RESULTS

NUTRIOSE® increased proliferation of Bacteroides and inhibited Clostridum perfringens in both studies, increased β-glucosidase activity (at 10 and 15 g/day) and decreased colonic pH (at 20 g/day). The increase in short-chain fatty acid production with NUTRIOSE® consumption was not statistically significant. There were no indications of gastrointestinal intolerance at any dose.

CONCLUSIONS

According to commonly accepted definitions, NUTRIOSE® is a prebiotic soluble fibre that provides a beneficial effect on colonic ecology while preserving digestive comfort.

What do we know about dietary fiber intake in children and health? The effects of fiber intake on constipation, obesity, and diabetes in children

The effect of dietary fiber intake on chronic diseases has been explored in adults but is largely unknown in children. This paper summarizes the currently existing evidence on the implications of dietary fiber intake on constipation, obesity, and diabetes in children. Current intake studies suggest that all efforts to increase children's dietary fiber consumption should be encouraged. Available data, predominantly from adult studies, indicate significantly lower risks for obesity, diabetes, and constipation could be expected with higher dietary fiber consumption. However, there is a lack of data from clinical studies in children of various ages consuming different levels of dietary fiber to support such assumptions. The existing fiber recommendations for children are conflicting, a surprising situation, because the health benefits associated with higher dietary fiber intake are well established in adults. Data providing conclusive evidence to either support or refute some, if not all, of the current pediatric fiber intake recommendations are lacking. The opportunity to improve children's health should be a priority, because it also relates to their health later in life. The known health benefits of dietary fiber intake, as summarized in this paper, call for increased awareness of the need to examine the potential benefits to children's health through increased dietary fiber.