Glucose and insulin response. (A) Glucose levels (milligrams per deciliter) obtained at 06:00 hours during the indicated week (age 27, 39, 52, and 65 weeks) for CON, CR, MET, and PF–MET (mean ± SD for all surviving rats). (B) Insulin levels (nanograms per milliliter) obtained at 06:00 hours during the indicated week (age 27, 39, 52, and 65 weeks; mean ± SD for 12 rats per study group). *p < .05. Note: CON = control; CR = calorie restriction; MET = metformin; PF–MET = pair fed to metformin.