We determined whether lower insulin sensitivity persists in young, nonobese, nondiabetic Mexican-American [MA; n = 13, 27.0 ± 2.0 yr, body mass index (BMI) 23.0 ± 0.7] compared with non-Hispanic white (NHW; n = 13, 24.8 ± 1.5 yr, BMI 22.8 ± 0.6) males and females after accounting for cardiorespiratory fitness (maximal O₂ uptake), abdominal fat distribution (computed tomography scans), dietary intake (4-day records), and skeletal muscle insulin-signaling protein abundance from muscle biopsies (Western blot analysis). MA were significantly less insulin sensitive compared with their NHW counterparts when estimated by homeostatic model assessment of insulin resistance (MA: 1.53 ± 0.22 vs. NHW: 0.87 ± 0.16, P < 0.05) and the revised quantitative insulin sensitivity check index (MA: 0.45 ± 0.08 vs. NHW: 0.58 ± 0.19, P = 0.05). However, skeletal muscle protein abundance of insulin receptor- (IR), phosphatidylinositol 3-kinase p85 subunit, Akt1, Akt2, and GLUT4 were not significantly different. Differences in indexes of insulin sensitivity lost significance after percent dietary intake of palmitic acid, palmitoleic acid, and skeletal muscle protein abundance of IR were accounted for. We conclude that differences in insulin sensitivity between nonobese, nondiabetic MA and NHW persist after effects of chronic and acute exercise and total and abdominal fat distribution are accounted for. These differences may be mediated, in part, by dietary fat intake.