Intrinsic dietary fibers and the gut microbiome: Rediscovering the benefits of the plant cell matrix for human health

Dietary fibre optimisation in support of global health

The human gut microbiota influences its host via multiple molecular pathways, including immune system interactions, the provision of nutrients and regulation of host physiology. Dietary fibre plays a crucial role in maintaining a healthy microbiota as its primary nutrient and energy source. Industrialisation has led to a massive decrease of habitual fibre intake in recent times, and fibre intakes across the world are below the national recommendations. This goes hand in hand with other factors in industrialised societies that may negatively affect the gut microbiota, such as medication and increased hygiene. Non-communicable diseases are on the rise in urbanised societies and the optimisation of dietary fibre intake can help to improve global health and prevent disease. Early life interventions shape the developing microbiota to counteract malnutrition, both in the context of industrialised nations with an overabundance of cheap, highly processed foods, as well as in Low- and Middle-Income Countries (LMICs). Adequate fibre intake should, however, be maintained across the life course to promote health. Here we will discuss the current state of dietary fibre research in the global context and consider different intervention approaches.

Dichotomous effect of dietary fiber in pediatrics: a narrative review of the health benefits and tolerance of fiber

Dietary fibers are associated with favorable gastrointestinal, immune, and metabolic health outcomes when consumed at sufficient levels. Despite the well-described benefits of dietary fibers, children and adolescents continue to fall short of daily recommended levels. This gap in fiber intake (i.e., "fiber gap") might increase the risk of developing early-onset pediatric obesity and obesity-related comorbidities such as type 2 diabetes mellitus into adulthood. The structure-dependent physicochemical properties of dietary fiber are diverse. Differences in solubility, viscosity, water-holding capacity, binding capability, bulking effect, and fermentability influence the physiological effects of dietary fibers that aid in regulating appetite, glycemic and lipidemic responses, and inflammation. Of growing interest is the fermentation of fibers by the gut microbiota, which yields both beneficial and less favorable end-products such as short-chain fatty acids (e.g., acetate, propionate, and butyrate) that impart metabolic and immunomodulatory properties, and gases (e.g., hydrogen, carbon dioxide, and methane) that cause gastrointestinal symptoms, respectively. This narrative review summarizes (1) the implications of fibers on the gut microbiota and the pathophysiology of pediatric obesity, (2) some factors that potentially contribute to the fiber gap with an emphasis on undesirable gastrointestinal symptoms, (3) some methods to alleviate fiber-induced symptoms, and (4) the therapeutic potential of whole foods and commonly marketed fiber supplements for improved health in pediatric obesity.

New Value of Acorus tatarinowii/gramineus Leaves as a Dietary Source for Dementia Prevention

The rhizomes of Acorus tatarinowii Schott and Acorus gramineus Solander are widely used for treating amnesia in traditional Chinese medicine. In contrast, their leaves are usually discarded without their medicinal properties being known. Here, we found that the hot water extract of leaves improved cognition and tau pathology in model mice of frontotemporal dementia, similar to or even better than that of rhizomes. To explore the optimal method of processing, we made three preparations from dried leaves: hot water extract, extraction residue, and non-extracted simple crush powder. Among them, the simple crush powder had the strongest effect on tauopathy in mice. The crush powder also ameliorated Aβ and α-synuclein pathologies and restored cognition in mouse models of Alzheimer's disease and dementia with Lewy bodies. These findings suggest the potential of Acorus tatarinowii/gramineus leaves as a dietary source for dementia prevention and reveal that simple crushing is a better way to maximize their efficacy.

Synthetic diets containing a single polysaccharide disrupt gut microbial community structure and microbial interaction networks in the American cockroach

Achieving and maintaining a healthy gut microbiome has numerous benefits for the host. Host diet plays a key role in shaping the gut microbial community, and understanding how diet composition influences gut microbiome structure and stability is key to developing effective interventions to treat gut microbiome dysbiosis. We use the American cockroach (Periplaneta americana) as a model system to dissect the response of gut microbes to host diet modification. Here, we designed synthetic diets from lab-grade, purified ingredients to identify how the cockroach gut community responds to different carbohydrate components (chitin, methylcellulose, microcrystalline cellulose, pectin, starch, xylan) in otherwise balanced diets. Using 16S rRNA gene sequencing, we show that synthetic diets produce replicable shifts in the cockroach gut community diversity and phylogenetic composition, with xylan-fed insects displaying the largest alterations. Comparison with cockroaches fed whole-food diets reveal that, rather than introducing new microbes, synthetic diets alter microbiome composition by inducing blooms among taxa present basally within the cockroach gut community. Synthetic diets are also associated with less-robust, more fragmentary microbial co-occurrence networks compared to cockroaches fed whole-food diets. Our results highlight the utility of lab-grade artificial diets in microbiome research and shed light on how purified polysaccharides may exert more influence over a stable gut community to generate noticeable change than whole food-derived fibers.

Effects of dietary fibre on metabolic health and obesity

Obesity and metabolic syndrome represent a growing epidemic worldwide. Body weight is regulated through complex interactions between hormonal, neural and metabolic pathways and is influenced by numerous environmental factors. Imbalances between energy intake and expenditure can occur due to several factors, including alterations in eating behaviours, abnormal satiation and satiety, and low energy expenditure. The gut microbiota profoundly affects all aspects of energy homeostasis through diverse mechanisms involving effects on mucosal and systemic immune, hormonal and neural systems. The benefits of dietary fibre on metabolism and obesity have been demonstrated through mechanistic studies and clinical trials, but many questions remain as to how different fibres are best utilized in managing obesity. In this Review, we discuss the physiochemical properties of different fibres, current findings on how fibre and the gut microbiota interact to regulate body weight homeostasis, and knowledge gaps related to using dietary fibres as a complementary strategy. Precision medicine approaches that utilize baseline microbiota and clinical characteristics to predict individual responses to fibre supplementation represent a new paradigm with great potential to enhance weight management efficacy, but many challenges remain before these approaches can be fully implemented.

Dietary Fiber in Inflammatory Bowel Disease: Are We Ready to Change the Paradigm?

Accumulating evidence from pre-clinical and clinical studies demonstrate the benefit of dietary fibers for inflammatory bowel disease (IBD). However, the majority of patients avoid or limit their consumption to manage their symptoms during the active and remission phases, although limited research supports these long-term dietary habits. Although recent evidence-based dietary guidelines highlight the importance of promoting an adequate intake of dietary fiber in IBD patients, intervention trials have not yet clearly clarified the quality and quantity of dietary fiber that should be consumed to be equally tolerated by and provide benefit for patients with IBD. This narrative review describes dietary fibers and their characteristics, analyzes the real-word studies on the impact of dietary fiber consumption in IBD in different clinical settings, and concludes with potential future directions in fiber research, focusing on the real-world needs of characterizing the consumption of fiber-rich foods and promoting their adequate intake.

Relationships between diet and gut microbiome in an Italian and Dutch cohort: does the dietary protein to fiber ratio play a role?

PURPOSE

To investigate the relationships between the habitual diet, the protein to fiber ratio (P/F), and the gut microbiome in one Italian and one Dutch cohort of healthy subjects consuming an omnivore diet.

METHODS

The Italian cohort included 19 males (M_IT, BMI 25.2 ± 0.72 kg/m2, age 25.4 ± 0.96 years) and 20 females (F_IT, BMI 23.9 ± 0.81 kg/m2, age 23.8 ± 0.54 years); the Dutch cohort included 30 females (F_NL, BMI: 23.9 ± 0.81 kg/m2, age: 23.8 ± 0.54 years). Individual diets were recorded through Food Frequency Questionnaires and analyzed to assess the nutrient composition. Gut microbiome was assessed in fecal samples.

RESULTS

M_IT consumed higher levels of proteins than F_NL and F_IT, whereas dietary fiber intake did not differ among groups. Data showed that consumption of plant protein to animal protein (PP/AP) and PP to total proteins ratio can determine a differentiation of F_NL more than the absolute amount of dietary fiber. Conversely, the protein to fiber (P/F) and AP to total proteins better characterized M_IT. M_IT harbored the highest abundance of proteolytic microorganisms and the lowest microbial gene richness. Conversely, F_NL had more fiber-degrading microorganisms like Bacteroides thetaiotaomicron, Bacteroides xylanisolvens, Roseburia sp., Coprococcus eutactus and Parabacteroides along with the highest number of genes encoding carbohydrate-active enzymes and gene richness. It was predicted that by each unit decrease in the P/F a 3% increase in gene richness occurred.

CONCLUSION

Study findings suggested that dietary P/F, rather than the absolute amount of dietary fiber, could contribute to the shaping of the microbiome towards a more proteolytic or fiber-degrading gut ecosystem.

CLINICALTRIALS

gov Identifier NCT04205045-01-10-2018, retrospectively registered. Dutch Trial Register NTR7531-05-10-2018.

Hawaiian native herb Mamaki prevents dementia by ameliorating neuropathology and repairing neurons in four different mouse models of neurodegenerative diseases

Neurodegenerative diseases including Alzheimer's disease, frontotemporal dementia, and dementia with Lewy bodies are age-related disorders and the main cause of dementia. They are characterized by the cerebral accumulation of Aβ, tau, α-synuclein, and TDP-43. Because the accumulation begins decades before disease onset, treatment should be started in the preclinical stage. Such intervention would be long-lasting, and therefore, prophylactic agents should be safe, non-invasively taken by the patients, and inexpensive. In addition, the agents should be broadly effective against etiologic proteins and capable of repairing neurons damaged by toxic oligomers. These requirements are difficult to meet with single-ingredient pharmaceuticals but may be feasible by taking proper diets composed of multiple ingredients. As a source of such diets, we focused on the Hawaiian native herb Mamaki. From its dried leaves and fruits, we made three preparations: hot water extract of the leaves, non-extracted simple crush powder of the leaves, and simple crush powder of the fruits, and examined their effects on the cognitive function and neuropathologies in four different mouse models of neurodegenerative dementia. Hot water extract of the leaves attenuated neuropathologies, restored synaptophysin levels, suppressed microglial activation, and improved memory when orally administered for 1 month. Simply crushed leaf powder showed a higher efficacy, but simply crushed fruit powder displayed the strongest effects. Moreover, the fruit powder significantly enhanced the levels of brain-derived neurotrophic factor expression and neurogenesis, indicating its ability to repair neurons. These results suggest that crushed Mamaki leaves and fruits are promising sources of dementia-preventive diets.

Properties of cell wall polysaccharides of raw nectarine fruits after treatment under conditions that modulate gastric digestion

The results of the study of the physicochemical properties of the high-molecular-weight soluble and insoluble components of nectarine cell walls obtained by fruit treatment under conditions that modulate of gastric digestion are presented. Homogenized nectarine fruits were sequentially treated by natural saliva and simulated gastric fluid (SGF) at pH 1.8 and 3.0. The isolated polysaccharides were compared with polysaccharides obtained by sequential extraction of nectarine fruit with cold, hot, and acidified water, solutions of ammonium oxalate and sodium carbonate. As a result, high-molecular-weight water-soluble pectic polysaccharides, weakly bound in the cell wall, were dissolved in the simulated gastric fluid, regardless of pH. Homogalacturonan (HG) and rhamnogalacturonan-I (RG-I) were identified in all pectins. It was shown that their quantity and ability to form highly viscous solutions determine high values of the rheological characteristics of the nectarine mixture formed under simulated gastric conditions. The modifications occurring with the insoluble components under the influence of acidity of SGF were importance. They determined difference in the physicochemical properties of both the insoluble fibres and the nectarine mixtures.

Weighted Gene Co-Expression Network Analysis Identifies a Functional Guild and Metabolite Cluster Mediating the Relationship between Mucosal Inflammation and Adherence to the Mediterranean Diet in Ulcerative Colitis

Diet influences the pathogenesis and clinical course of inflammatory bowel disease (IBD). The Mediterranean diet (MD) is linked to reductions in inflammatory biomarkers and alterations in microbial taxa and metabolites associated with health. We aimed to identify features of the gut microbiome that mediate the relationship between the MD and fecal calprotectin (FCP) in ulcerative colitis (UC). Weighted gene co-expression network analysis (WGCNA) was used to identify modules of co-abundant microbial taxa and metabolites correlated with the MD and FCP. The features considered were gut microbial taxa, serum metabolites, dietary components, short-chain fatty acid and bile acid profiles in participants that experienced an increase (n = 13) or decrease in FCP (n = 16) over eight weeks. WGCNA revealed ten modules containing sixteen key features that acted as key mediators between the MD and FCP. Three taxa (Faecalibacterium prausnitzii, Dorea longicatena, Roseburia inulinivorans) and a cluster of four metabolites (benzyl alcohol, 3-hydroxyphenylacetate, 3-4-hydroxyphenylacetate and phenylacetate) demonstrated a strong mediating effect (ACME: -1.23, p = 0.004). This study identified a novel association between diet, inflammation and the gut microbiome, providing new insights into the underlying mechanisms of how a MD may influence IBD. See clinicaltrials.gov (NCT04474561).

Gut microbiome-modulated dietary strategies in EAE and multiple sclerosis

Over the last few decades, the incidence of multiple sclerosis has increased as society's dietary habits have switched from a whole foods approach to a high fat, high salt, low dietary fiber, and processed food diet, termed the "Western diet." Environmental factors, such as diet, could play a role in the pathogenesis of multiple sclerosis due to gut microbiota alterations, gut barrier leakage, and subsequent intestinal inflammation that could lead to exacerbated neuroinflammation. This mini-review explores the gut microbiome alterations of various dietary strategies that improve upon the "Western diet" as promising alternatives and targets to current multiple sclerosis treatments. We also provide evidence that gut microbiome modulation through diet can improve or exacerbate clinical symptoms of multiple sclerosis, highlighting the importance of including gut microbiome analyses in future studies of diet and disease.

To Fiber or Not to Fiber: The Swinging Pendulum of Fiber Supplementation in Patients with Inflammatory Bowel Disease

Evidence-based dietary guidance around dietary fiber in inflammatory bowel disease (IBD) has been limited owing to insufficient reproducibility in intervention trials. However, the pendulum has swung because of our increased understanding of the importance of fibers in maintaining a health-associated microbiome. Preliminary evidence suggests that dietary fiber can alter the gut microbiome, improve IBD symptoms, balance inflammation, and enhance health-related quality of life. Therefore, it is now more vital than ever to examine how fiber could be used as a therapeutic strategy to manage and prevent disease relapse. At present, there is limited knowledge about which fibers are optimal and in what form and quantity they should be consumed to benefit patients with IBD. Additionally, individual microbiomes play a strong role in determining the outcomes and necessitate a more personalized nutritional approach to implementing dietary changes, as dietary fiber may not be as benign as once thought in a dysbiotic microbiome. This review describes dietary fibers and their mechanism of action within the microbiome, details novel fiber sources, including resistant starches and polyphenols, and concludes with potential future directions in fiber research, including the move toward precision nutrition.