Serum concentrations of insulin and FABP4 were determined by sandwich ELISA. The primary antibodies were as follows: anti‐insulin and anti‐FABP4 (Abcam, Cambridge, UK). The absorbance was determined at 450 nm on a microplate reader (Tecan Group AG, Männedorf, Switzerland). The level of nonesterified fatty acids (NEFAs) was detected using the Free Fatty Acid Assay Kit (Abcam, Cambridge, UK) according to the manufacturer's instructions.
Mouse blood was dropped onto a glucose test strip (Accu‐Check Active, Roche) and measured by a glucometer (Accu‐Check Active, Roche). For the glucose tolerance test (IP‐GTT), mice were given an intraperitoneal injection (ip) of 100 mg/mL D‐glucose (2 g/kg body weight) after overnight fasting, and blood glucose concentrations were monitored. For the insulin tolerance test (IP‐ITT), mice were fasted for 4 hours before ip administration of human insulin (0.75 U/kg body weight, Santa Cruz Biotechnology, Dallas, TX), and blood glucose concentrations were monitored.