Fiber — the forgotten ally of the gut?

Aim of the study: Dysfunction of the gut microbiota is frequently reported as a manifestation of chronic diseases, and therefore presents as a modifiable risk factor in their development. Diet is a major regulator of the gut microbiota, and certain types of dietary fiber may modify bacterial numbers and metabolism, including short-chain fatty acid (SCFA) generation.

Results: A total of 64 studies involving 2099 participants were included. Compared with placebo or low-fiber controls, dietary fiber intervention resulted in higher abundance of Bifidobacterium spp. (standardized mean difference (SMD): 0.64; 95% CI: 0.42, 0.86; P < 0.00001) and Lactobacillus spp. (SMD: 0.22; 0.03, 0.41; P = 0.02), as well as higher fecal butyrate concentration (SMD: 0.24; 0.00, 0.47; P = 0.05). Subgroup analysis showed that fructans and galacto-oligosaccharides led to significantly greater abundance of both Bifidobacterium spp. and Lactobacillus spp. than the controls (P < 0.00001 and P = 0.002, respectively). No differences in effect were found between fiber intervention and controls for α-diversity, the abundance of other specified bacteria, or the concentrations of other SCFAs. Dietary fiber intervention, particularly with fructans and galacto-oligosaccharides, increases fecal abundance of Bifidobacterium and Lactobacillus spp. but does not affect α-diversity.

Aim of the study: Inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC), contributes to substantial morbidity. Understanding the intricate interplay between dietary factors and the incidence and progression of IBD is essential for developing effective preventative and therapeutic strategies.

Results: The associations with dietary patterns are reflected in inflammatory biomarkers. IBD is typically treated with medication; however, many patients have a suboptimal response to medical treatment. The findings from this umbrella review could provide evidence for nutritional counseling and be a valuable addition to traditional IBD treatment plans. This systematic review was registered with PROSPERO as CRD440252.

Aim of the study: Epidemiological studies have consistently demonstrated the benefits of dietary fibre for gastrointestinal health through the consumption of unrefined whole foods, such as wholegrains, legumes, vegetables and fruits.

Results: In this Review, we detail the major physicochemical properties and functional characteristics of dietary fibres, the importance of dietary fibres and current evidence for their use in the management of gastrointestinal disorders. It is now well-established that the physicochemical properties of different dietary fibres (such as solubility, viscosity and fermentability) vary greatly depending on their origin and processing and are important determinants of their functional characteristics and clinical utility. Although progress in understanding these relationships has uncovered potential therapeutic opportunities for dietary fibres, many clinical questions remain unanswered, such as clarity on the optimal dose, type and source of fibre required both to manage clinical symptoms and to prevent gastrointestinal disorders. The use of novel fibres and/or the co-administration of fibres is an additional therapeutic approach yet to be extensively investigated.

Aim of the study: Despite the accepted health benefits of consuming dietary fiber, little is known about the mechanisms by which fiber deprivation impacts the gut microbiota and alters disease risk.

Results: Using a gnotobiotic mouse model, in which animals were colonized with a synthetic human gut microbiota composed of fully sequenced commensal bacteria, we elucidated the functional interactions between dietary fiber, the gut microbiota, and the colonic mucus barrier, which serves as a primary defense against enteric pathogens. We show that during chronic or intermittent dietary fiber deficiency, the gut microbiota resorts to host-secreted mucus glycoproteins as a nutrient source, leading to erosion of the colonic mucus barrier. Dietary fiber deprivation, together with a fiber-deprived, mucus-eroding microbiota, promotes greater epithelial access and lethal colitis by the mucosal pathogen, Citrobacter rodentium. Our work reveals intricate pathways linking diet, the gut microbiome, and intestinal barrier dysfunction, which could be exploited to improve health using dietary therapeutics.

Aim of the study: 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.

Results: 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-being 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.

Aim of the study: Dietary fiber is a widely recognized nutrient for human health. Previous studies proved that dietary fiber has significant implications for gastrointestinal health by regulating the gut microbiota.

Results: Moreover, mechanistic research showed that the physiological functions of different dietary fibers depend to a great extent on their physicochemical characteristics, one of which is solubility. Compared with insoluble dietary fiber, soluble dietary fiber can be easily accessed and metabolized by fiber-degrading microorganisms in the intestine and produce a series of beneficial and functional metabolites. In this review, we outlined the structures, characteristics, and physiological functions of soluble dietary fibers as important nutrients. We particularly focused on the effects of soluble dietary fiber on human health via regulating the gut microbiota and reviewed their effects on dietary and clinical interventions.

Aim of the study: Excessive consumption of the simple sugar fructose, which induces excessive hepatic lipogenesis and gut dysbiosis, is a risk factor for cardiometabolic diseases. Here we show in male mice that the gut microbiome, when adapted to dietary fibre inulin, catabolizes dietary fructose and mitigates or reverses insulin resistance, hepatic steatosis and fibrosis.

Results: Inulin also activates hepatic de novo serine synthesis and cystine uptake, augmenting glutathione production and protecting the liver from fructose-induced lipid peroxidation. These multi-modal effects of inulin are transmittable by the gut microbiome, where Bacteroides acidifaciens acts as a key player. Thus, the gut microbiome, adapted to use inulin (a fructose polymer), efficiently catabolizes dietary monomeric fructose, thereby protecting the host. These findings provide a mechanism for how fibre can facilitate the gut microbiome to mitigate the host's exposure to harmful nutrients and disease progression.

Aim of the study: Diet is a key factor in regulating gut microbiota homeostasis, thereby influencing the incidence, severity, and prognosis of acute pancreatitis (AP). This review categorizes common dietary patterns into harmful types (Western diet, high-fat diet, ketogenic diet, high-salt diet) and beneficial types (Mediterranean diet, high-fiber diet, plant-based diet, restricted diet).

Results: Unlike previous reviews that list dietary patterns one by one, this paper analyzes them within the framework of the four core pathological/protective pathways of AP. Harmful diets primarily exacerbate AP by inducing dysbiosis, reducing SCFAs (especially butyrate), impairing the gut barrier, promoting bacterial translocation and excessive inflammatory responses; beneficial diets alleviate AP progression by enriching probiotics, increasing SCFA synthesis, enhancing barrier integrity, and suppressing systemic inflammation. This paper particularly emphasizes that most current evidence comes from non-AP models such as obesity and inflammatory bowel disease, and AP-specific causal evidence remains very limited. By integrating clinical, animal, and cellular experimental evidence, this paper aims to elucidate the potential relationship between diet, gut microbiota, and AP, and to provide a theoretical basis for dietary intervention strategies targeting the gut microbiota.

Aim of the study: Maternal nutrition during pregnancy is a critical determinant of offspring long-term health. Dietary fiber has emerged as a key modifiable factor.

Results: Animal studies demonstrate that maternal fiber deprivation impairs offspring glucose metabolism, promotes low-grade inflammation and obesity, and compromises immune tolerance, whereas fiber or short-chain fatty acid (SCFA) supplementation confers protective effects. Human observational studies support these findings, showing associations between maternal SCFA levels and favorable neonatal metabolic profiles, neurodevelopmental outcomes, and reduced obesity risk, although randomized controlled trials remain limited. Key translational challenges include inter-species differences, individual microbiome variability, and optimal intervention timing. Despite these uncertainties, promoting adequate and diverse dietary fiber intake during pregnancy represents a safe, low-cost, and scalable public health strategy to improve intergenerational health outcomes.