(A) Body weight (BW) and composition of young (4–5 months) and aged (18–21 months) mice (n = 9 mice per group). Vertical axis shows mass in grams for BW, Lean and Fat, or body composition as percentage of fat for Fat%. (B) Blood glucose levels in overnight fasted and ad libitum fed mice (n = 9 mice per group). (C) Plasma insulin levels in overnight fasted and ad libitum fed mice (horizontal bars represent median, n = 7 fasted mice per group and 9–10 fed mice per group). (D) Glucose tolerance test (n = 9 mice per group). *, p < 0.05; comparison by 2-way repeated measures ANOVA (left panel) or Student’s t test (right panel). (E) Plasma insulin levels 15 minutes after glucose injection (horizontal bars represent mean, n = 6 young + 7 aged mice). *, p < 0.05; comparison by Student’s t-test. (F) Plasma C-peptide levels 15 minutes after glucose injection (horizontal bars indicate mean, n = 6 young + 7 aged mice). *, p < 0.05; comparison by Student’s t-test. (G) Insulin tolerance test (n = 9 mice per group). Data are presented as mean ± SEM unless stated otherwise.