Obesity decreases naive T cells and expands memory cells. Chow-fed control mice and mice fed a high-fat (60%) diet were evaluated for naive (CD62L⁺CD44⁻; red box) E/M (CD62L⁻CD44⁺) CD4 and CD8 T cells at 3 months (n = 10-12/group), 9 months (n = 8/group), and 13 months (n = 12/group) of age. Obesity significantly reduces naive cells (top left quadrant) and expands E/M splenic T cells (bottom right quadrant) in 9- and 13-month-old mice but not at 3 months of age.