Inulin and prebiotics — what should we feed the good bacteria?

Aim of the study: Inulin-type fructans (ITF), including short-chain fructooligosaccharides (scFOS), oligofructose, and inulin, are commonly used fibers that are widely regarded as prebiotic for their ability to be selectively utilized by the intestinal microbiota to confer a health benefit.

Results: Evidence from studies included in the current review suggest that ITF have a prebiotic effect on the intestinal microbiota, promoting the abundances of Bifidobacterium, Lactobacillus, and Faecalibacterium prausnitzii. Beneficial health effects reported following ITF intake include improved intestinal barrier function, improved laxation, increased insulin sensitivity, decreased triglycerides and an improved lipid profile, increased absorption of calcium and magnesium, and increased satiety. Although there is some evidence for differing effects of ITF based on chain length, the lack of direct comparisons and detailed descriptions of physicochemical properties limits the ability to draw conclusions from human clinical studies.

Aim of the study: Compared to a healthy population, the gut microbiota in type 2 diabetes presents with several unfavourable features that may impair glucose regulation. The aim of this study was to evaluate the prebiotic effect of inulin-type fructans on the faecal microbiota and short-chain fatty acids (SCFA) in patients with type 2 diabetes.

Results: Treatment with inulin-type fructans induced moderate changes in the faecal microbiota composition (1.5%, p = 0.045). A bifidogenic effect was most prominent, with highest positive effect on operational taxonomic units (OTUs) of Bifidobacterium adolescentis, followed by OTUs of Bacteroides. Significantly higher faecal concentrations of total SCFA, acetic acid and propionic acid were detected after prebiotic consumption compared to placebo. The prebiotic fibre had no effects on the concentration of butyric acid or on the overall microbial diversity. Six weeks supplementation with inulin-type fructans had a significant bifidogenic effect and induced increased concentrations of faecal SCFA, without changing faecal microbial diversity. Our findings suggest a moderate potential of inulin-type fructans to improve gut microbiota composition and to increase microbial fermentation in type 2 diabetes.

Aim of the study: Gut dysbiosis that resulted from the alteration between host-microbe interaction might worsen obesity-induced systemic inflammation. Gut microbiota manipulation by supplementation of prebiotic inulin may reverse metabolic abnormalities and improve obesity. This study aimed to determine whether inulin supplementation improved intestinal microbiota and microbial functional pathways in children with obesity.

Results: One hundred and forty-three children with available taxonomic and functional pathway abundance profiles were evaluated. A significant increase in alpha-diversity was observed in the inulin group. Inulin supplementation substantially enhanced Bifidobacterium, Blautia, Megasphaera, and several butyrate-producing bacteria, including Agathobacter, Eubacterium coprostanoligenes, and Subdoligranulum, compared to the other groups. The inulin group showed a significant difference in functional pathways of proteasome and riboflavin metabolism. These changes correlated with clinical and metabolic outcomes exclusively in the inulin group. Inulin supplementation significantly promoted gut bacterial diversity and improved gut microbiota dysbiosis in children with obesity. The modulation of functional pathways by inulin suggests its potential to establish beneficial interactions between the gut microbiota and host physiology.

Aim of the study: Contrary to the long-standing prerequisite of inducing selective (ie, bifidogenic) effects, recent findings suggest that prebiotic interventions lead to ecosystem-wide microbiota shifts. Yet, a comprehensive characterisation of this process is still lacking.

Results: While faecal metabolite profiles were not significantly altered by inulin consumption, our analyses did detect a modest effect on global microbiota composition and specific inulin-induced changes in relative abundances of Anaerostipes, Bilophila and Bifidobacterium were identified. The observed decrease in Bilophila abundances following inulin consumption was associated with both softer stools and a favourable change in constipation-specific quality-of-life measures. Ecosystem-wide analysis of the effect of a dietary intervention with prebiotic inulin-type fructans on the colon microbiota revealed that this effect is specifically associated with three genera, one of which (Bilophila) representing a promising novel target for mechanistic research.

Aim of the study: Modulating the gut microbiota with prebiotics is a promising strategy for managing metabolic diseases. However, the clinical effects on glycemic metabolism across different populations remain uncertain. In this study, we conducted a randomized, double-blind investigation to examine the impact of inulin and fructooligosaccharides (FOS) on glycemic metabolism in overweight/obese and healthy adults.

Results: Placebo had no effect on glycemic metabolism or gut microbiota. Inulin significantly reduced glucose levels at 1 h (Cohen's d = 0.71, p = 0.041) and 2 h (Cohen's d = 0.73, p = 0.028) during oral glucose tolerance test (OGTT), increased fasting insulin (Cohen's d = 0.70, p = 0.008), and lowered homocysteine (HCY) levels (Cohen's d = 0.76, p = 0.014) in overweight/obese individuals. These effects were not observed in healthy individuals. In contrast, although FOS significantly decreased HCY (Cohen's d = 0.72, p = 0.023), it did not improve glycemic metrics in either group. Inulin also reduced the abundance of Ruminococcus by 72.0% (from 1.661% ± 1.501% to 0.465% ± 0.594%), positively correlating with improved glycemic outcomes. Propionate levels decreased significantly in both overweight/obese (Cohen's d = 0.89, p = 0.014) and healthy participants (Cohen's d = 1.19, p = 0.020) following inulin.

Aim of the study: Prebiotic inulin improves obesity-related metabolic disturbances, yet its clinical efficacy shows marked interindividual heterogeneity. The key microbial players, interspecies interactions, and downstream effector pathways governing differential responsiveness remain poorly defined.

Results: Butyrate conferred protection by strengthening gut barrier function, activating GLP-1/PYY secretion, and suppressing adipose inflammation. We uncover a novel D. desulfuricans-H2S-R. intestinalis-butyrate antagonistic axis that mechanistically explains inulin response heterogeneity, providing a mechanistic rationale for personalized nutrition and supporting a clinically translatable predictive index and targeted intervention strategy.

Aim of the study: Rapidly fermentable prebiotic substrates occupy a contradictory position in human nutrition. In microbiome and functional-food research, low molecular weight non-digestible carbohydrates such as inulin, fructo-oligosaccharides, and galacto-oligosaccharides are added to foods and supplements to promote bifidogenic, metabolic and gastrointestinal benefits.

Results: Rapidly fermentable substrates may support beneficial microbial and metabolic responses in tolerant individuals, but may contribute to gas production, osmotic effects, luminal distension, symptom generation or even immune activation in susceptible contexts. Future research should move beyond defining prebiotic efficacy primarily by enrichment of selected bacterial taxa. Instead, each substrate should be tested through dose-response studies that establish both beneficial and tolerance thresholds across healthy individuals and clinically relevant phenotypes. Future studies should also examine prebiotics within a host-ecology framework, testing whether benefit depends less on maximising microbial stimulation and more on maintaining a controlled, spatially contained and clinically tolerable microbiome.