Mechanisms of crude Idesia polycarpa oil in regulating metabolic syndrome via the gut-liver axis: a multidimensional functional analysis based on dietary fat source variations

Idesia polycarpa crude oil (I. polycarpa crude oil), rich in linoleic acid, has long been consumed in southwestern China, but its health effects remain unclear. At the same time, the impact of low-fat/high-carbohydrate diets (LFD) on metabolic disorders is still debated. This study used GC-MS, 16S rRNA sequencing, metabolomics, and biochemical/histological analyses to compare I. polycarpa crude oil with olive, lard, rapeseed, and soybean oils in mice fed LFD or high-fat/low-carbohydrate diets (HFD). Mice consuming I. polycarpa crude oil showed more severe liver and intestinal injury than those fed olive oil, lard, or soybean oil, but milder than rapeseed oil, with effects dependent on diet. Under LFD, the I. polycarpa crude oil group (LID) exhibited higher Lactobacillus abundance (0.3126 vs. 0.0046, 0.0328, 0.0137 %), and Rumphellolide B (2.38 vs. 0.04, 0.07, 0.04) than olive, lard, and rapeseed oils, but not soybean oil. Under HFD, the I. polycarpa crude oil group (HID) showed markedly increased Gastranaerophilales abundance (5.01×10⁻⁵ vs. 0.0033, 0.0016, 0.0012, 0.0005 %) and vanillin (58.21 vs. 4.21, 4.13, 4.13, 2.90) compared with all other oils. The five dietary oils did not result in significant differences in antioxidant enzyme activity (SOD, GSH-Px), cytokine levels (IL-4, IL-6, TNF-α), or intestinal permeability between the LFD and HFD groups. Among the oils tested, beechwood crude oil induced milder symptoms compared with rapeseed oil, but more pronounced symptoms than olive oil, lard, and soybean oil. Although certain indicators did not differ significantly between the LFD and HFD groups, the overall health benefits of LFD were less favorable than commonly presumed.