Dietary fiber intake is broadly associated with reduced colorectal cancer (CRC) risk, but results vary by fiber type and processing. The mechanistic basis for how structurally distinct fibers shape the gut microbiome and metabolome to influence colon tumorigenesis remains unclear. This preclinical study tested whether different purified fibers produce distinct microbiome and metabolic states that alter susceptibility to sporadic colon cancer in an AOM model.
The authors aimed to determine whether structurally distinct dietary fibers differentially modulate colon tumor development and to characterize the underlying gut microbiome and metabolic mechanisms responsible for any observed effects.
Four-week-old male mice were assigned to either a low-fiber control diet or to diets supplemented with 7.5% (w/w) of one of four purified fibers: cellulose, agar, pectin, or inulin. Feeding continued for 28 weeks. Mice received eight intraperitoneal injections of azoxymethane (AOM, 7.5 mg/kg) to model sporadic carcinogen-driven colon tumorigenesis.
Temporal fecal microbiomes were profiled using 16S rRNA sequencing. Cecal metabolites were quantified by proton nuclear magnetic resonance (1H-NMR) spectroscopy. Microbiome–metabolome interactions and community structure were assessed using co-occurrence network analyses. In vitro functional testing included assessing the effect of cecal extracts on HT29 colorectal cancer cell proliferation.
Refined inulin supplementation produced a markedly higher colon tumor incidence (~70%) relative to the other diet groups, which had tumor incidences of approximately 10–20%. Cecal extracts obtained from inulin-fed animals promoted proliferation of HT29 cancer cells in vitro, providing a functional correlate to the in vivo tumor findings.
Longitudinal 16S-rRNA sequencing revealed 36 microbial taxa or signatures specifically associated with inulin supplementation. These inulin-specific signatures converged on two principal functional axes:
These community shifts were identified in the context of AOM exposure and were linked to the high tumor incidence observed in the inulin group.
Metabolomic profiling of cecal contents confirmed the functional consequences of the microbiome changes. Under AOM exposure, inulin-fed animals showed accumulation of fermentation intermediates such as succinate, fumarate, and lactate, together with depletion of propionate and several amino acids. Notably, these metabolite differences were not observed in carcinogen-naive animals, indicating that the carcinogen exposure amplified or revealed metabolomic vulnerabilities tied to the inulin-conditioned microbiome.
Network analyses identified two stable co-occurrence hubs that appeared exclusively in AOM-treated animals. These hubs structurally integrated taxa and functions from both identified axes — the disrupted fermentation/SCFA axis and the reprogrammed amino acid/nitrogen metabolism axis — consistent with a community-level reorganization linking microbial composition and metabolic outputs to tumor-promoting conditions.
The study provides evidence that a purified, refined inulin supplement can precondition the gut microbiome toward a functionally vulnerable ecosystem marked by reduced fermentation throughput and altered amino acid metabolism. When combined with carcinogen exposure (AOM), this preconditioned state is amplified into a tumor-promoting environment, which coincided with a substantially higher colon tumor incidence in inulin-fed mice and with cecal extracts that enhanced HT29 cell proliferation in vitro.
These results suggest that fiber type matters: not all dietary fibers exert the same effects on the gut microbiome–metabolome axis or on colon tumor susceptibility in this mouse AOM model. The findings support a mechanistic link between fiber-type-specific microbiome remodeling, altered cecal metabolite profiles, and increased tumorigenesis under carcinogen challenge.
Limitations and context: the report is a preprint and has not been peer reviewed. Details beyond those summarized in the published abstract (for example, full taxon lists, exact effect sizes for metabolites beyond reported directions, or additional experimental controls) were not reported in the abstract and would require consultation of the full preprint and supplementary material.
Overall, the study highlights the need to consider fiber structure and microbial functional outcomes when evaluating dietary fiber interventions for colorectal cancer prevention.