The primary objective is to demonstrate in healthy young men and women (14-18.9 y at baseline) with habitually low usual milk and milk product intakes that intervention with greater milk and milk product consumption improves lumbar spine BMD in a dose-response manner over 2 y (while accounting for body size, physical activity, demographics and age). Healthy young men and women will be recruited and screened for usual intake of milk and milk products. Those with low intakes < 2 servings of milk or milk products will be randomized (stratified by sex and age) to 1 of 3 groups for the RCT (n=10090/group): maintain usual low intakes (<1 serving), improved intakes (average of 2 servings/d) or recommended intakes (≥3 servings/d) of milk and milk products. A manualized motivational interviewing framework will be used for the interventions. Those meeting recommendations at screening will form a longitudinal cohort for 2 y. Key measurements include baseline and yearly assessment of BMD at multiple sites plus interim assessment of general health, anthropometry, dietary intakes, physical activity and biomarkers of calcium homeostasis; and in the young adults bone metabolism.