Agilent 7890b 7000d system

Collected samples were stored at $-30°\mathrm{C}$ until being used in experiments. Serum ( $25\mathrm{\mu }\mathrm{L}$ ) obtained via cardiac puncture during euthanasia, feces from the small intestine ( $15\mathrm{\mu }\mathrm{g}$ ), and liver tissue ( $15\mathrm{\mu }\mathrm{g}$ ) samples were used for measuring free fatty acids. A fatty acid methylation kit (Nacalai Tesque) was used to analyze the methylation of samples. Gas chromatography–mass spectrometry (GC-MS) was performed using an Agilent 7890B/7000D system (Agilent Technologies) to measure palmitic acid levels in murine sera, feces, and liver tissues ( $n=10$ ). The final product was loaded onto a Varian capillary column (DB-FATWAX UI; Agilent Technologies). The capillary column used for fatty acid separation was CP-Sil 88 for FAME [ $100\mathrm{m}\times 0.25\mathrm{mm}$
$\left(\text{inner diameter}\right)\times 0.20\mathrm{\mu }\mathrm{m}$ (membrane thickness); Agilent Technologies]. The column was maintained at 100°C for 4 min, and the temperature was then increased gradually by 3°C/min to 240°C and held for 7 min. The sample was injected in split mode with a split ratio of 5:1. Each fatty acid methyl ester was detected in the selected ion-monitoring mode. All the results were normalized to the peak height for the C17:0 internal standard.^{55 (link)}