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.     

Health Benefits of Fiber Fermentation

Although fiber is well recognized for its effect on laxation, increasing evidence supports the role of fiber in the prevention and treatment of chronic disease. The aim of this review is to provide an overview of the health benefits of fiber and its fermentation, and describe how the products of fermentation may influence disease risk and treatment. Higher fiber intakes are associated with decreased risk of cardiovascular disease, type 2 diabetes, and some forms of cancer. Fiber may also have a role in lowering blood pressure and in preventing obesity by limiting weight gain. Fiber is effective in managing blood glucose in type 2 diabetes, useful for weight loss, and may provide therapeutic adjunctive roles in kidney and liver disease. In addition, higher fiber diets are not contraindicated in inflammatory bowel disease or irritable bowel syndrome and may provide some benefit. Common to the associations with disease reduction is fermentation of fiber and its potential to modulate microbiota and its activities and inflammation, specifically the production of anti-inflammatory short chain fatty acids, primarily from saccharolytic fermentation, versus the deleterious products of proteolytic activity. Because fiber intake is inversely associated with all-cause mortality, mechanisms by which fiber may reduce chronic disease risk and provide therapeutic benefit to those with chronic disease need further elucidation and large, randomized controlled trials are needed to confirm causality.Teaching Points? Strong evidence supports the association between higher fiber diets and reduced risk of cardiovascular disease, type 2 diabetes, and some forms of cancer.? Higher fiber intakes are associated with lower body weight and body mass index, and some types of fiber may facilitate weight loss.? Fiber is recommended as an adjunctive medical nutritional therapy for type 2 diabetes, chronic kidney disease, and certain liver diseases.? Fermentation and the resulting shifts in microbiota composition and its activity may be a common means by which fiber impacts disease risk and management.     

Prebiotics and the Human Gut Microbiota: From Breakdown Mechanisms to the Impact on Metabolic Health

The colon harbours a dynamic and complex community of microorganisms, collectively known as the gut microbiota, which constitutes the densest microbial ecosystem in the human body. These commensal gut microbes play a key role in human health and diseases, revealing the strong potential of fine-tuning the gut microbiota to confer health benefits. In this context, dietary strategies targeting gut microbes to modulate the composition and metabolic function of microbial communities are of increasing interest. One such dietary strategy is the use of prebiotics, which are defined as substrates that are selectively utilised by host microorganisms to confer a health benefit. A better understanding of the metabolic pathways involved in the breakdown of prebiotics is essential to improve these nutritional strategies. In this review, we will present the concept of prebiotics, and focus on the main sources and nature of these components, which are mainly non-digestible polysaccharides. We will review the breakdown mechanisms of complex carbohydrates by the intestinal microbiota and present short-chain fatty acids (SCFAs) as key molecules mediating the dialogue between the intestinal microbiota and the host. Finally, we will review human studies exploring the potential of prebiotics in metabolic diseases, revealing the personalised responses to prebiotic ingestion. In conclusion, we hope that this review will be of interest to identify mechanistic factors for the optimization of prebiotic-based strategies.     

Therapeutic Benefits and Dietary Restrictions of Fiber Intake: A State of the Art Review

Throughout history, malnutrition and deficiency diseases have been a problem for our planet’s population. A balanced diet significantly influences everyone’s health, and fiber intake appears to play a more important role than previously thought. The natural dietary fibers are a category of carbohydrates in the constitution of plants that are not completely digested in the human intestine. High-fiber foods, such as fruits, vegetables and whole grains, have consistently been highly beneficial to health and effectively reduced the risk of disease. Although the mode of action of dietary fiber in the consumer body is not fully understood, nutritionists and health professionals unanimously recognize the therapeutic benefits. This paper presents the fiber consumption in different countries, the metabolism of fiber and the range of health benefits associated with fiber intake. In addition, the influence of fiber intake on the intestinal microbiome, metabolic diseases (obesity and diabetes), neurological aspects, cardiovascular diseases, autoimmune diseases and cancer prevention are discussed. Finally, dietary restrictions and excess fiber are addressed, which can cause episodes of diarrhea and dehydration and increase the likelihood of bloating and flatulence or even bowel obstruction. However, extensive studies are needed regarding the composition and required amount of fiber in relation to the metabolism of saprotrophic microorganisms from the enteral level and the benefits of the various pathologies with which they can be correlated.     

Cecal infusion of butyrate does not alter cecal concentration of butyrate in piglets fed inulin

BACKGROUND: Cecal or distal colonic concentration of butyrate has been used as an index of butyrate production from various fermentable carbohydrates. However, we previously found that cecal concentration of butyrate does not correlate with the rate of synthesis of butyrate in the cecal lumen. As part of a larger study of the cellular effects of cecal infusions of butyrate, we sought to rule out the null hypothesis that cecal infusion of butyrate also would not alter butyrate concentration in the cecum. METHODS: Piglets (n = 10) were fed sow milk replacement formula plus inulin (3 g x L(-1)). After 6 days of oral feeding, the piglets were randomly assigned into 2 equal groups: (I) Cecal infusion of phosphate-buffered NaCl and (II) cecal infusion of butyrate (2.13 micromol x kg(-1) x min(-1)). The concentration of butyrate was measured by gas chromatography in the cecum and distal colon. RESULTS: There was no effect of cecal butyrate infusion on butyrate concentration (mM; I vs II) in the cecum (5.7 +/- 0.4 vs 5.3 +/- 1.1) or distal colon (3.3 +/- 0.6 vs 4.1 +/- 0.8) or on the ratio of cecal butyrate concentration to the sum of the concentrations of butyrate, acetate, propionate, and valerate (0.101 +/- 0.004 vs 0.083 +/- 0.011). There was no effect of cecal butyrate infusion on the concentration of any of these short chain fatty acids. CONCLUSIONS: At an entry rate into the cecum within the physiological range, butyrate had no effect on cecal or distal colonic luminal concentration of butyrate.     

Dietary Factors Modulating Colorectal Carcinogenesis

The development of colorectal cancer, responsible for 9% of cancer-related deaths, is favored by a combination of genetic and environmental factors. The modification of diet and lifestyle may modify the risk of colorectal cancer (CRC) and prevent neoplasia in up to 50% of cases. The Western diet, characterized by a high intake of fat, red meat and processed meat has emerged as an important contributor. Conversely, a high intake of dietary fiber partially counteracts the unfavorable effects of meat through multiple mechanisms, including reduced intestinal transit time and dilution of carcinogenic compounds. Providing antioxidants (e.g., vitamins C and E) and leading to increased intraluminal production of protective fermentation products, like butyrate, represent other beneficial and useful effects of a fiber-rich diet. Protective effects on the risk of developing colorectal cancer have been also advocated for some specific micronutrients like vitamin D, selenium, and calcium. Diet-induced modifications of the gut microbiota modulate colonic epithelial cell homeostasis and carcinogenesis. This can have, under different conditions, opposite effects on the risk of CRC, through the production of mutagenic and carcinogenic agents or, conversely, of protective compounds. The aim of this review is to summarize the most recent evidence on the role of diet as a potential risk factor for the development of colorectal malignancies, as well as providing possible prevention dietary strategies.     

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).     

Physiological Effects of Resistant Starches on Fecal Bulk,Short Chain Fatty Acids,Blood Lipids and Glycemic Index

Objective: To assess the effects on fecal bulking, fecal short chain fatty acid (SCFA) production, blood lipids and glycemic indices of two different forms of resistant starch (RS₂ and RS₃) from a high-amylose cornstarch.

Methods: Twenty-four healthy subjects (12 men; 12 women) consumed four supplements taken for 2 weeks in random order separated by 2-week washout periods. The supplements were a low-fiber (control) and supplements providing an additional 30 g dietary fiber as wheat bran (high-fiber control) or the equivalent amount of resistant starch analyzed gravimetrically as dietary fiber from RS₂ or RS₃. Four-day fecal collections and 12-hour breath gas collections were obtained at the end of each period. Fasting blood was taken at the beginning and end of each period. Glycemic indices of supplements were also assessed.

Results: The wheat bran supplement increased fecal bulk 96±14 g/day compared with the low-fiber control (p<0.001) with the mean for both resistant starches also being greater (22±8 g/day) than the low-fiber control (p=0.013). On the resistant starch phases, the mean fecal butyrate:SCFA ratio, which has been suggested to have positive implications for colonic health, was significantly above the low-fiber control by 31±14% (p=0.035). Resistant starches did not alter serum lipids, urea or breath H₂ or CH₄. No significant differences in glycemic index were seen between the RS and control supplements.

Conclusion: The potential physiological benefits of the resistant starches studied appear to relate to colonic health in terms of effects on fecal bulk and SCFA metabolism.     

Faecal microbiota and short‐chain fatty acids in patients receiving enteral nutrition with standard or fructo‐oligosaccharides and fibre‐enriched formulas

Background: Prebiotics potentially increase the growth of bifidobacteria, which may minimise the risk of diarrhoea in patients receiving enteral nutrition (EN). The present study aimed to compare the concentrations of faecal microbiota and short‐chain fatty acids (SCFA) in patients receiving EN with either a standard formula or one enriched with fructo‐oligosaccharides (FOS) and fibre. Methods: Forty‐one hospitalised adult patients (25 males, 16 females) who were on exclusive EN for at least 12 days were recruited to a cross‐sectional study. Faecal samples were collected and analysed for major groups of microbiota using fluorescent in situ hybridisation and SCFA concentrations were analysed using gas liquid chromatography. Results: There were generally low concentrations of the major bacterial groups, including bifidobacteria, in all patients receiving either standard or FOS/fibre‐enriched formula [bifidobacteria: 6.6 (1.3) versus 7.0 (2.0) log₁₀ cells g^?1 dry faecal, P = 0.199]. However, faecal butyrate concentrations were higher in patients receiving the FOS/fibre‐enriched formula compared to standard formula [20.5 (21.6) versus 4.6 (6.7) μmol g^?1 dry faecal, P = 0.006]. Conclusions: Low concentrations of faecal bifidobacteria were identified in these patients, which potentially increases their risk of diarrhoea. Other microbiota groups may utilise FOS/fibre, leading to different butyrate concentrations between the two cohorts.     

Composition of Dietary Fatty Acids and Health Risks in Japanese Youths

In the overall composition of dietary fatty acids (FAs), the quantity of each FA is interrelated with that of others. We examined the associations between dietary FA composition and cardiometabolic risk in Japanese youths. Risk factors (anthropometric characteristics, serum lipid and liver enzyme levels, and blood pressure) were measured in 5485 junior-high-school students. Dietary intake was assessed using a food frequency questionnaire. The mean saturated FA (SFA), monounsaturated FA (MUFA), omega-6 polyunsaturated FAs (PUFAs), and omega-3 PUFAs intake were 9.6%E, 10.3%E, 6.3%E, and 1.1%E, respectively. In compositional regression analysis controlled for confounders, a high intake of omega-6 PUFAs relative to others was associated with low low-density-lipoprotein cholesterol levels (LDL-C; p = 0.003), and relative SFA intake was associated with high levels of gamma-glutamyl transpeptidase (p = 0.019). Relative omega-3 PUFAs intake was associated with low blood pressure (p = 0.005–0.034) but had unfavorable effects on adiposity and alanine transaminase. Substitutional models showed similar results for omega-6 PUFAs on LDL-C, but MUFA had inconsistent effects on risk factors. The results from the compositional data analysis were consistent with previous studies and clinical practice/knowledge. Focusing on increasing omega-6 PUFAs in Japanese youths could have favorable consequences in the long term.     

Nutrition and Health Claims Spectra of Pre-Packaged Foods on Serbian Supermarket Shelves: A Repeated Cross-Sectional Study

Nutrition and health claims (NHCs) are a powerful tool that influence consumers’ final decision on the choice of food products. The purposes of this repeated cross-sectional study were to (i) assess the prevalence of pre-packaged food products containing nutrition and health claims among different food categories, (ii) to determine the type of NHCs labelled on the examined food products, and (iii) to evaluate the trend in the use of NHCs in comparison to the 2012 survey. The survey was conducted immediately before the full enforcement of the new national legislation on NHCs in 2020. It comprised 3141 pre-packaged food products from 10 product categories. In total, 21.2% of food products contained any claim (19.4% contained any nutrition claim; 8.2% contained any health claim). In comparison to the 2012 survey, we observed a rising trend in the presence of NHCs; the use of nutrition claims on food products increased three times and the use of health claims increased 1.3 times in the 2020 survey. Bearing in mind that NHCs are a powerful tool guiding consumers’ food purchase decisions, NHCs should be supported by precise legislation and strict surveillance by the public health authorities.     

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.     

燕麦β-葡聚糖对小鼠结肠菌群及其功能的影响

目的:研究燕麦β-葡聚糖对小鼠结肠菌群及其功能的影响。方法:体重23～25g的健康昆明种小鼠126只,分成7组,每组18只,实验组(1～6组)分别以高低剂量0.5g和0.25g/(㎏bw·d)灌胃给予燕麦β-葡聚糖OG2600、OG340和OG5,对照组给予相同体积的生理盐水,灌胃期28d。分别于实验14、28和35d(停止灌胃后1w)分析各组小鼠结肠双歧杆菌、乳酸杆菌和大肠杆菌的变化;并在实验28d用气相色谱法测定小鼠结肠中短链脂肪酸的含量;用流式细胞仪分析结肠粘膜上皮细胞变化。结果:与对照组比,随着灌胃时间的延长,各实验组均可使小鼠肠道和粪便中的双歧杆菌和乳酸杆菌增殖,使大肠杆菌数量减少,作用效果与分子大小和剂量有关;第2、4、6组小鼠结肠内容物的乙酸、丙酸、丁酸的量显著高于对照组(P<0.05);第6组细胞增殖指数和对照组有显著差异(P<0.05)。结论:燕麦β-葡聚糖具有调节小鼠肠道菌群的作用;在体内容易发酵产生较高比例的短链脂肪酸,能促进结肠粘膜上皮细胞的增殖。     

A Cross-Sectional Audit of Nutrition and Health Claims on Dairy Yoghurts in Supermarkets of the Illawarra Region of New South Wales,Australia

Health and nutrition claims are used by consumers to guide purchasing decisions. In consequence, monitoring and evaluation of such claims to ensure they are accurate and transparent is required. The aim of this study was to investigate the use of nutrition and health claims on dairy-yoghurt products within select Australian supermarkets and assess their compliance with the revised Food Standards Code (FSC). Nutrition, health, and related claims on yoghurt products were assessed in a cross-sectional audit of five supermarkets in the Illawarra region of New South Wales. Claim prevalence, type, and compliance were assessed and products were compared against current rating measures. A total of n = 340 dairy yoghurt products were identified. Most products (97.9%) carried at least one nutrition and/or health claim, with nutrition-content claims (93.9%) the most prevalent. Most products (n = 277) met the nutrient profiling scoring criterion; while 87.9% of products did not carry the health star rating. Almost all claims surveyed (97.4%) were compliant with the FSC. Health and nutrition claims are highly prevalent across yoghurt categories, with the majority of these compliant with regulations. The ambiguity surrounding the wording and context of claims challenges researchers to investigate consumers’ interpretations of health messaging within the food environment.     

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.     

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.     

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.     

Alterations in Fecal Short-Chain Fatty Acids after Bariatric Surgery: Relationship with Dietary Intake and Weight Loss

Bariatric surgery is associated with weight loss attributed to reduced caloric intake, mechanical changes, and alterations in gut hormones. However, some studies have suggested a heightened incidence of colorectal cancer (CRC) has been associated with bariatric surgery, emphasizing the importance of identifying mechanisms of risk. The objective of this study was to determine if bariatric surgery is associated with decreases in fecal short-chain fatty acids (SCFA), a group of bacterial metabolites of fiber. Fecal samples (n = 22) were collected pre- (~6 weeks) and post-bariatric surgery (~4 months) in patients undergoing Roux-en-Y gastric bypass and sleeve gastrectomy. SCFA levels were quantified using liquid chromatography/mass spectrometry. Dietary intake was quantified using 24-h dietary recalls. Using an aggregate variable, straight SCFAs significantly decreased by 27% from pre- to post-surgery, specifically acetate, propionate, butyrate, and valerate. Pre-surgery weight was inversely associated with butyrate, with no association remaining post-surgery. Multiple food groups were positively (sugars, milk, and red and orange vegetables) and inversely (animal protein) associated with SCFA levels. Our results suggest a potential mechanism linking dietary intake and SCFA levels with CRC risk post-bariatric surgery with implications for interventions to increase SCFA levels.