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Research into the analysis, physical properties and health effects of dietary fibre has continued steadily over the last 40–50 years. From the knowledge gained, countries have developed guidelines for their populations on the optimal amount of fibre to be consumed each day. Food composition tables from many countries now contain values for the dietary fibre content of foods, and, from these, combined with dietary surveys, population intakes have been determined. The present review assessed the uniformity of the analytical methods used, health claims permitted, recommendations and intakes, particularly from national surveys across Europe and around the world. It also assessed current knowledge on health effects of dietary fibre and related the impact of different fibre types on health. The overall intent was to be able to provide more detailed guidance on the types of fibre which should be consumed for good health, rather than simply a total intake figure, the current situation. Analysis of data indicated a fair degree of uniformity in the definition of dietary fibre, the method used for analysis, the recommended amount to be consumed and a growing literature on effects on digestive health and disease risk. However, national dietary survey data showed that intakes do not reach recommendations and very few countries provide guidance on the types of fibre that are preferable to achieve recommended intakes. Research gaps were identified and ideas suggested to provide information for more detailed advice to the public about specific food sources that should be consumed to achieve health benefits.

Fibre is promoted as part of a healthy dietary pattern and in diabetes management. We have considered the role of high-fibre diets on mortality and increasing fibre intake on glycaemic control and other cardiometabolic risk factors of adults with prediabetes or diabetes. We conducted a systematic review of published literature to identify prospective studies or controlled trials that have examined the effects of a higher fibre intake without additional dietary or other lifestyle modification in adults with prediabetes, gestational diabetes, type 1 diabetes, and type 2 diabetes. Meta-analyses were undertaken to determine the effects of higher fibre intake on all-cause and cardiovascular mortality and increasing fibre intake on glycaemic control and a range of cardiometabolic risk factors. For trials, meta regression analyses identified further variables that influenced the pooled findings. Dose response testing was undertaken; Grading of Recommendations Assessment, Development and Evaluation (GRADE) protocols were followed to assess the quality of evidence. Two multicountry cohorts of 8,300 adults with type 1 or type 2 diabetes followed on average for 8.8 years and 42 trials including 1,789 adults with prediabetes, type 1, or type 2 diabetes were identified. Prospective cohort data indicate an absolute reduction of 14 fewer deaths (95% confidence interval (CI) 4-19) per 1,000 participants over the study duration, when comparing a daily dietary fibre intake of 35 g with the average intake of 19 g, with a clear dose response relationship apparent. Increased fibre intakes reduced glycated haemoglobin (HbA1c; mean difference [MD] -2.00 mmol/mol, 95% CI -3.30 to -0.71 from 33 trials), fasting plasma glucose (MD -0.56 mmol/L, 95% CI -0.73 to -0.38 from 34 trials), insulin (standardised mean difference [SMD] -2.03, 95% CI -2.92 to -1.13 from 19 trials), homeostatic model assessment of insulin resistance (HOMA IR; MD -1.24 mg/dL, 95% CI -1.72 to -0.76 from 9 trials), total cholesterol (MD -0.34 mmol/L, 95% CI -0.46 to -0.22 from 27 trials), low-density lipoprotein (LDL) cholesterol (MD -0.17 mmol/L, 95% CI -0.27 to -0.08 from 21 trials), triglycerides (MD -0.16 mmol/L, 95% CI -0.23 to -0.09 from 28 trials), body weight (MD -0.56 kg, 95% CI -0.98 to -0.13 from 18 trials), Body Mass Index (BMI; MD -0.36, 95% CI -0·55 to -0·16 from 14 trials), and C-reactive protein (SMD -2.80, 95% CI -4.52 to -1.09 from 7 trials) when compared with lower fibre diets. All trial analyses were subject to high heterogeneity. Key variables beyond increasing fibre intake were the fibre intake at baseline, the global region where the trials were conducted, and participant inclusion criteria other than diabetes type. Potential limitations were the lack of prospective cohort data in non-European countries and the lack of long-term (12 months or greater) controlled trials of increasing fibre intakes in adults with diabetes. Higher-fibre diets are an important component of diabetes management, resulting in improvements in measures of glycaemic control, blood lipids, body weight, and inflammation, as well as a reduction in premature mortality. These benefits were not confined to any fibre type or to any type of diabetes and were apparent across the range of intakes, although greater improvements in glycaemic control were observed for those moving from low to moderate or high intakes. Based on these findings, increasing daily fibre intake by 15 g or to 35 g might be a reasonable target that would be expected to reduce risk of premature mortality in adults with diabetes.

The consumption of whole grain products is often related to beneficial effects on consumer health. Dietary fibre is an important component present in whole grains and is believed to be (at least partially) responsible for these health benefits. The dietary fibre composition of whole grains is very distinct over different grains. Whole grains of cereals and pseudo-cereals are rich in both soluble and insoluble functional dietary fibre that can be largely classified as e.g., cellulose, arabinoxylan, β-glucan, xyloglucan and fructan. However, even though the health benefits associated with the consumption of dietary fibre are well known to scientists, producers and consumers, the consumption of dietary fibre and whole grains around the world is substantially lower than the recommended levels. This review will discuss the types of dietary fibre commonly found in cereals and pseudo-cereals, their nutritional significance and health benefits observed in animal and human studies.

To estimate the dietary share of ultra-processed foods and to determine its association with the overall nutritional quality of diets in Brazil. Cross-sectional. Brazil. A representative sample of 32 898 Brazilians aged ≥10 years was studied. Food intake data were collected. We calculated the average dietary content of individual nutrients and compared them across quintiles of energy share of ultra-processed foods. Then we identified nutrient-based dietary patterns, and evaluated the association between quintiles of dietary share of ultra-processed foods and the patterns' scores. The mean per capita daily dietary energy intake was 7933 kJ (1896 kcal), with 58·1 % from unprocessed or minimally processed foods, 10·9 % from processed culinary ingredients, 10·6 % from processed foods and 20·4 % from ultra-processed foods. Consumption of ultra-processed foods was directly associated with high consumption of free sugars and total, saturated and trans fats, and with low consumption of protein, dietary fibre, and most of the assessed vitamins and minerals. Four nutrient-based dietary patterns were identified. 'Healthy pattern 1' carried more protein and micronutrients, and less free sugars. 'Healthy pattern 2' carried more vitamins. 'Healthy pattern 3' carried more dietary fibre and minerals and less free sugars. 'Unhealthy pattern' carried more total, saturated and trans fats, and less dietary fibre. The dietary share of ultra-processed foods was inversely associated with 'healthy pattern 1' (-0·16; 95 % CI -0·17, -0·15) and 'healthy pattern 3' (-0·18; 95 % CI -0·19, -0·17), and directly associated with 'unhealthy pattern' (0·17; 95 % CI 0·15, 0·18). Dietary share of ultra-processed foods determines the overall nutritional quality of diets in Brazil.

Observational studies have shown that dietary fiber intake is associated with decreased risk of cardiovascular disease. Dietary fiber is a non-digestible form of carbohydrates, due to the lack of the digestive enzyme in humans required to digest fiber. Dietary fibers and lignin are intrinsic to plants and are classified according to their water solubility properties as either soluble or insoluble fibers. Water-soluble fibers include pectin, gums, mucilage, fructans, and some resistant starches. They are present in some fruits, vegetables, oats, and barley. Soluble fibers have been shown to lower blood cholesterol by several mechanisms. On the other hand, water-insoluble fibers mainly include lignin, cellulose, and hemicellulose; whole-grain foods, bran, nuts, and seeds are rich in these fibers. Water-insoluble fibers have rapid gastric emptying, and as such may decrease the intestinal transit time and increase fecal bulk, thus promoting digestive regularity. In addition to dietary fiber, isolated and extracted fibers are known as functional fiber and have been shown to induce beneficial health effects when added to food during processing. The recommended daily allowances (RDAs) for total fiber intake for men and women aged 19–50 are 38 gram/day and 25 gram/day, respectively. It is worth noting that the RDA recommendations are for healthy people and do not apply to individuals with some chronic diseases. Studies have shown that most Americans do not consume the recommended intake of fiber. This review will summarize the current knowledge regarding dietary fiber, sources of food containing fiber, atherosclerosis, and heart disease risk reduction.

Background: Dietary fibre consists of non-digestible forms of carbohydrate, usually as polysaccharides that originate from plant-based foods. Over recent decades, our diet within Westernised societies has changed radically from that of our hominid ancestors, with implications for our co-evolved gut microbiota. This includes increased ingestion of ultra-processed foods that are typically impoverished of dietary fibre, and associated reduction in the intake of fibre-replete plant-based foods. Over recent decades, there has been a transformation in our understanding of the health benefits of dietary fibre. Objective: To explore the current medical literature on the health benefits of dietary fibre, with a focus on overall metabolic health. Data Sources: We performed a narrative review, based on relevant articles written in English from a PubMed search, using the terms ‘dietary fibre and metabolic health’. Results: In the Western world, our diets are impoverished of fibre. Dietary fibre intake associates with overall metabolic health (through key pathways that include insulin sensitivity) and a variety of other pathologies that include cardiovascular disease, colonic health, gut motility and risk for colorectal carcinoma. Dietary fibre intake also correlates with mortality. The gut microflora functions as an important mediator of the beneficial effects of dietary fibre, including the regulation of appetite, metabolic processes and chronic inflammatory pathways. Conclusions: Multiple factors contribute to our fibre-impoverished modern diet. Given the plethora of scientific evidence that corroborate the multiple and varied health benefits of dietary fibre, and the risks associated with a diet that lacks fibre, the optimization of fibre within our diets represents an important public health strategy to improve both metabolic and overall health. If implemented successfully, this strategy would likely result in substantial future health benefits for the population.

A major challenge in affluent societies is the increase in disorders related to gut and metabolic health. Chronic over nutrition by unhealthy foods high in energy, fat, and sugar, and low in dietary fibre is a key environmental factor responsible for this development, which may cause local and systemic inflammation. A low intake of dietary fibre is a limiting factor for maintaining a viable and diverse microbiota and production of short-chain fatty acids in the gut. A suppressed production of butyrate is crucial, as this short-chain fatty acid (SCFA) can play a key role not only in colonic health and function but also at the systemic level. At both sites, the mode of action is through mediation of signalling pathways involving nuclear NF-κB and inhibition of histone deacetylase. The intake and composition of dietary fibre modulate production of butyrate in the large intestine. While butyrate production is easily adjustable it is more variable how it influences gut barrier function and inflammatory markers in the gut and periphery. The effect of butyrate seems generally to be more consistent and positive on inflammatory markers related to the gut than on inflammatory markers in the peripheral tissue. This discrepancy may be explained by differences in butyrate concentrations in the gut compared with the much lower concentration at more remote sites.

In mice on a low microbiota-accessible carbohydrate (MAC) diet, the diversity of the gut microbiota is depleted, and the effect is transferred and compounded over generations; this phenotype is only reversed after supplementation of the missing taxa via faecal microbiota transplantation, suggesting dietary intervention alone may by insufficient at managing diseases characterized by a dysbiotic microbiota. Effect of diet on gut microbiota Over our history, humans have experienced major dietary changes, including a shift to low-fibre intake in Westernized populations, which is paralleled by a general loss in the diversity of the gut microbiota. Microbiota-accessible carbohydrates (MACs), which are abundant in dietary fibre, are the primary source of carbon and energy for the distal gut microbiota. This study shows that in mice on a low-MAC diet, the diversity of the microbiota is depleted and that this effect is transferred and compounded over generations, such that the low abundant taxa are progressively lost from one generation to the next, particularly those of the order Bacteroidales, which are proficient in the consumption of dietary fibre. This phenotype is not reversible simply by reintroducing dietary MACs, but requires supplementation of the missing taxa via faecal microbiota transplantation. These findings suggest that a change in diet alone may be insufficient to restore a healthy microbiota in individuals with dysbiosis. The gut is home to trillions of microorganisms that have fundamental roles in many aspects of human biology, including immune function and metabolism 1 , 2 . The reduced diversity of the gut microbiota in Western populations compared to that in populations living traditional lifestyles presents the question of which factors have driven microbiota change during modernization. Microbiota-accessible carbohydrates (MACs) found in dietary fibre have a crucial involvement in shaping this microbial ecosystem, and are notably reduced in the Western diet (high in fat and simple carbohydrates, low in fibre) compared with a more traditional diet 3 . Here we show that changes in the microbiota of mice consuming a low-MAC diet and harbouring a human microbiota are largely reversible within a single generation. However, over several generations, a low-MAC diet results in a progressive loss of diversity, which is not recoverable after the reintroduction of dietary MACs. To restore the microbiota to its original state requires the administration of missing taxa in combination with dietary MAC consumption. Our data illustrate that taxa driven to low abundance when dietary MACs are scarce are inefficiently transferred to the next generation, and are at increased risk of becoming extinct within an isolated population. As more diseases are linked to the Western microbiota and the microbiota is targeted therapeutically, microbiota reprogramming may need to involve strategies that incorporate dietary MACs as well as taxa not currently present in the Western gut.

ObjectiveDietary fibres are essential for maintaining microbial diversity and the gut microbiota can modulate host physiology by metabolising the fibres. Here, we investigated whether the soluble dietary fibre oligofructose improves host metabolism by modulating bacterial transformation of secondary bile acids in mice fed western-style diet.DesignTo assess the impact of dietary fibre supplementation on bile acid transformation by gut bacteria, we fed conventional wild-type and TGR5 knockout mice western-style diet enriched or not with cellulose or oligofructose. In addition, we used germ-free mice and in vitro cultures to evaluate the activity of bacteria to transform bile acids in the caecal content of mice fed with western-style diet enriched with oligofructose. Finally, we treated wild-type and TGR5 knockout mice orally with hyodeoxycholic acid to assess its antidiabetic effects.ResultsWe show that oligofructose sustains the production of 6α-hydroxylated bile acids from primary bile acids by gut bacteria when fed western-style diet. Mechanistically, we demonstrated that the effects of oligofructose on 6α-hydroxylated bile acids were microbiota dependent and specifically required functional TGR5 signalling to reduce body weight gain and improve glucose metabolism. Furthermore, we show that the 6α-hydroxylated bile acid hyodeoxycholic acid stimulates TGR5 signalling, in vitro and in vivo, and increases GLP-1R activity to improve host glucose metabolism.ConclusionModulation of the gut microbiota with oligofructose enriches bacteria involved in 6α-hydroxylated bile acid production and leads to TGR5-GLP1R axis activation to improve body weight and metabolism under western-style diet feeding in mice.

A high-fat diet (HFD) can easily induce obesity and change the gut microbiota and its metabolites. However, studies on the effects of high-fat diets on the host have drawn inconsistent results. In this study, the unexpected results showed that the refined HFD increased gut microbiota diversity and short-chain fatty acids (SCFAs), causing an increase in energy metabolism. Further analysis revealed these changes were caused by the different fiber content in these two diets. Male C57BL/6J mice (4–5 weeks old) were fed either HFD or refined low-fat diet (LFD) for 14 weeks. The metabolic rates, thermogenesis, gut microbiome, and intestinal SCFAs were tested. The HFD triggered obesity and disturbed glucose homeostasis. Mice fed HFD ingested more fiber than mice fed LFD (p < 0.0001), causing higher intestinal SCFA concentrations related to the increased abundances of specific bacteria in the HFD group. Also, the HFD increased metabolic heat and up-regulated thermogenesis genes uncoupling protein 1(Ucp-1), peroxisome proliferator-activated receptor-γ coactivator-1α (Pgc-1α) expression in the brown adipose tissue (BAT). It was revealed by 16S rRNA gene sequencing that the HFD increased gut microbial diversity, which enriched Desulfovibrionaceae, Rikenellaceae RC9 gut group, and Mucispirillum, meanwhile, reduced the abundance of Lactobacillus, Bifidobacterium, Akkermansia, Faecalibaculum, and Blautia. The predicted metabolic pathways indicated HFD increased the gene expression of non-absorbed carbohydrate metabolism pathways, as well as the risks of colonization of intestinal pathogens and inflammation. In conclusion, the HFD was obesogenic in male C57BL/6J mice, and increased fiber intake from the HFD drove an increase in gut microbiota diversity, SCFAs, and energy expenditure. Meanwhile, the differences in specific nutrient intake can dissociate broad changes in energy expenditure, gut microbiota, and its metabolites from obesity, raising doubts in the previous studies. Therefore, it is necessary to consider whether differences in specific nutrient intake will interfere with the results of the experiments.