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.

The contents of basic chemical components in the whole fruit, pulp and seeds of two cultivars of Idesia polycarpa var. vestita Diels, Chongqing 1 and 2, at different growth periods were compared, and the composition and proportion of fatty acids in whole fruit oils were analyzed by gas chromatography (GC). The results showed that for both cultivars, there was a significant difference in the contents of crude fat, protein, total sugar, ash, total phenols, total flavonoids and other components among different growth periods and fruit parts (P < 0.05). The optimal harvest times for the two cultivars for oil production were about 198 and 182 days after full bloom, respectively. The main fatty acids in the oil of each part of the fruit were palmitic acid (C_16:0), palmitoleic acid (C_{16:1 cis}), and stearic acid (C_18:0), oleic acid (C_{18:1 cis}), linoleic acid (C_{18:2 cis}), α-linolenic acid (C_{18:3 n3}), γ-linolenic acid (C_{18:3 n6}) and arachidic acid (C_20:0). The relative contents of linoleic acid, unsaturated fatty acid and polyunsaturated fatty acid all showed the following decreasing order: seeds > fruit > pulp, and the relative content of linoleic acid in seeds was 75%. The results of principal component analysis (PCA) showed that the seeds had a relatively high comprehensive score and thus could be suitable for comprehensive utilization.