Sucrose-free low-fat diet induces metabolic dysfunction through gut dysbiosis and colonic inflammation in mice

Low-fat diets are widely promoted as health-protective; however, the consequences of removing sucrose within a low-fat dietary framework remain unclear. Here, we investigated the effects of a sucrose-free low-fat diet (SF-LFD) compared with a sucrose-containing low-fat control diet (C-LFD) in mice (n=6/group) over 16 weeks. Despite unchanged body and liver weights, SF-LFD feeding resulted in impaired glucose tolerance, reduced insulin sensitivity, and broad alterations in circulating metabolic hormones, including elevated C-peptide, incretins, ghrelin, and resistin, as well as reduced fasting insulin. 16S rRNA sequencing revealed that SF-LFD markedly disrupted gut microbial diversity and composition, with depletion of short-chain fatty acid-producing commensals, including Lactobacillus murinus and members of the Lachnospiraceae family, and enrichment of taxa associated with inflammatory or stress-adapted states, including Helicobacter ganmani, Odoribacter splanchnicus, and Alistipes species. This dysbiosis was accompanied by pronounced colonic inflammation characterized by crypt architectural disruption, loss of goblet cells, submucosal expansion, increased CD3⁺ T-cell and F4/80⁺ macrophage infiltration, and robust upregulation of inflammatory mediators, including Il1b, Il6, Ccl2, Rorγt, and Tbx21. SF-LFD feeding induced hepatic microvesicular steatosis, lobular inflammation, recruitment of F4/80⁺ and CD11c⁺ immune cells and increased hepatic expression of IL1b and IL6. Together, these findings suggest that sucrose elimination from a low-fat diet disrupts gut microbiota, impairs metabolic homeostasis, and promotes gut and liver inflammation, revealing an unrecognized dietary trigger of metabolic dysfunction.