Introduction: Insulin-like growth factor I (IGF-I) and IGF binding protein 3 (IGFBP-3) have been associated with increased risk of breast cancer. Methods: We report our findings on the effects of 16 weeks of aerobic exercise on IGF axis proteins, insulin, glucose, and insulin resistance of 319 young sedentary women. Demographics, health surveys, body composition, dietary intake, and blood samples were collected at baseline and 16 weeks. IGF-I and IGFBP-1, IGFBP-2, and IGFBP-3 were measured by ELISA. Results: Exercise adherence was 88%. The dropout rates for the exercise and control groups were 21.7% and 14.5%, respectively. There was a small significant change from baseline in IGFBP-3 concentrations. IGFBP-3 levels decreased in controls and increased in exercisers. The between-group difference was significant. No other changes were noted. Conclusion: Sixteen weeks of exercise had minimum or no effect on IGF proteins of young women. Impact: Our study supports findings from previous studies conducted in older populations and raises the question of what type of intervention is needed to change circulating levels of IGF proteins in humans.