The Degree of Inulin Polymerization Is Important for Short-Term Amelioration of High-Fat Diet (HFD)-Induced Metabolic Dysfunction and Gut Microbiota Dysbiosis in Rats

Abstract

Inulin, a non-digestible polysaccharide, has gained attention for its prebiotic properties, particularly in the context of obesity, a condition increasingly understood as a systemic inflammatory state linked to gut microbiota composition. This study investigates the short-term protective effects of inulin with different degrees of polymerization (DPn) against metabolic health deterioration and gut microbiota alterations induced by a high-fat diet (HFD) in Sprague Dawley rats. Inulin treatments with an average DPn of 7, 14, and 27 were administered at 1 g/kg of bodyweight to HFD-fed rats over 21 days. Body weight, systemic glucose levels, and proinflammatory markers were measured to assess metabolic health. Gut microbiota composition was analyzed through 16S rRNA gene sequencing. The results showed that inulin₂₇ significantly reduced total weight gain and systemic glucose levels, suggesting a DPn-specific effect on metabolic health. The study also observed shifts in gut microbial populations, with inulin₇ promoting several beneficial taxa from the Bifidobacterium genera, whilst inducing a unique microbial composition compared to medium-chain (DPn 14) and long-chain inulin (DPn: 27). However, the impact of inulin on proinflammatory markers and lipid metabolism parameters was not statistically significant, possibly due to the short study duration. Inulin with a higher DPn has a more pronounced effect on mitigating HFD-induced metabolic health deterioration, whilst inulin₇ is particularly effective at inducing healthy microbial shifts. These findings highlight the benefits of inulin as a dietary adjuvant in obesity management and the importance of DPn in optimizing performance.

Keywords: dysbiosis; fructooligosaccharides; gut microbiome; inulin; metabolic disease; obesity; prebiotics.

Figure 1

(A) Normalized change in rodent bodyweight over 21 days of HFD and treatment with inulin of various DPn. (B) The total bodyweight gain at day 21 was significantly reduced for inulin₂₇ compared to all other groups. Statistical significance is annotated as * p < 0.05, and ** p ≤ 0.01.

Figure 2

(A) Systemic glucose was reduced by inulin27, whilst (B) glycated hemoglobin A1C levels remained the same for all groups at 21 days of inulin treatment for HFD-fed rats. Statistical significance is annotated as * p < 0.05.

Figure 3

Metabolic markers of health measured from rats after 21 days of treatment. (A) Serum IL-6 concentration, (B) TNF-α concentration, (C) HDL concentration, and (D) triglyceride concentrations were not affected by inulin treatments.

Figure 4

The relative abundance taxa at the family level are shown for each rat sample (top) and the combined treatment groups (bottom). Inulin₇ showed lower abundance of Lachnospiraceae associated with metabolic disease, whilst promoting Bifidobacteriaceae taxa containing several beneficial commensal species.

Figure 5

Alpha-diversity presented as box-and-whisker plots illustrating no statistical differences amongst inulin treatments and the HFD group in terms of (A) the total number of species or OTUs across treatments, (B) Simpson’s index (accounting for the number of species and the abundance of each species), and (C) Shannon index (considering both the abundance and evenness of the species present).

Figure 6

Beta-diversity is presented as PCoA plots, with each illustrating differences between inulin₇ and all other groups using (A) Bray–Curtis dissimilarity (representing the differences in species composition between samples); and (B) Jaccard index (the presence and absence of species used to visualize the dissimilarity between the samples). (C) Hierarchical k-mer clustering (k-mer length = 16) represents the phylogenetic distance between the HFD (■), inulin₇ (▲), inulin₁₄ (▲) and inulin₂₇ (◆) microbial compositions.

Figure 7

Differential abundance analysis showing statistically significant differences (p < 0.05) in the total abundance of all species for rats that were treated with either (A) inulin₇, (B) inulin₁₄, or (C) inulin₂₇ compared to the HFD group. Species depicted in red have been reduced, and blue have been promote, compared to the HFD group.

Figure 8

(A) Transepithelial electrical resistance (TEER) of Caco-2 cell monolayers measured at 1 h and 24 h following LPS (0–1000 mg/L) removal from the culture medium. Concentrations of 500 and 1000 mg/L of LPS are sufficient to induce sustained Caco-2 monolayer layer after 24 h. (B) The recovery of TEER when SCFAs are added to the culture medium at 10 mol/m³ following LPS (500 mg/L) exposure at 0 h, 3 h, 18 h, and 24 h reveals only butyrate restores TEER, whilst all treatments show decreased (C) FITC-dextran permeability after LPS exposure. TEER was measured at each timepoint as the % of Transwell initial TEER measurement prior to the start of treatment. Statistical significance is annotated as * p < 0.05, ** p ≤ 0.01, *** p ≤ 0.001, or **** p ≤ 0.0001.

Figure 9

Cecal and fecal concentrations of (A) total cumulative SCFAs content, (B) acetic acid, (C) propionic acid, and (D) butyric acid are increased by inulin₁₄ administration to HFD-fed rats. Statistical significance is annotated as * p < 0.05, and ** p ≤ 0.01.

Figure 10

Cell-free supernatant (CFS) at 1 g/L of inulin₁₄ fermented by commensal Blautia strains recovered TEER across the Caco-2 cells following LPS (500 g/L) damage. (A) TEER was measured at each timepoint as the % of Transwell initial TEER measurement prior to the start of treatment. (B) FITC-dextran permeability across the Caco-2 cell monolayers measured following LPS exposure was unaffected by CFS at all concentrations. Statistical significance is annotated as * p < 0.05, and ** p ≤ 0.01.