Glucose tolerance tests and insulin tolerance tests

Glucose tolerance tests (GTTs) and insulin tolerance tests (ITTs) were performed as previously described 49. Briefly, GTTs were performed at 16 weeks of age (1 g/kg of body weight of dextrose) after an overnight fast on mice fed a NCD or a HFD. Dextrose (Hospira, Inc., Lake Forest, IL) was diluted in injection grade water and administered by oral gavage (Solomon Scientific, San Antonio, TX). ITTs were performed at 17 weeks of age, after a 5 h fast. Humulin R insulin (Eli Lilly and Co., Indianapolis, IN) was diluted in 0.9% saline (Phoenix Pharmaceutical, Inc., Burlingame, CA) and administered by intraperitoneal injection at 0.75 U/kg of body weight and glucose values were measured as using OneTouch Ultra 2 glucometer.