|Appropriate assessment of overweight and obesity in adolescents is a critical aspect in medical care. During adolescence weight gain carries a higher risk for adult obesity and the metabolic syndrome. Early adolescence is a high-risk time for weight gain due to the synergy of naturally occurring metabolic changes. One of the first potential health effects of abnormal weight gain during this period is earlier puberty, usually called as thelarche. The obesity epidemic is clearly implicated in the national trend toward earlier thelarche. Leptin activation of the hypothalamic-pituitary axis, combined with insulin resistance, and increased adiposity may result in the higher estrogen levels that are linked to breast development. Physical activity has been directly linked to overweight status in overweight early adolescents. In fact, when multiple diet sedentary, and activity behaviours were studied, the only factor shown to be predictive of a higher BMI in adolescent boys was decreased physical activity.