Introduction Body mass index (BMI) during adolescence is highly influenced by the pubertal maturation, and early maturation has been associated with overweight, but it is still uncertain if these factors are just a cluster of conditions or whether pubertal maturation influence BMI increments. This study aimed to examine the influence of sexual maturation (SM) on fatness and BMI increments during adolescence among Brazilians aged between 9 and 13 years.

Methods 598 girls and 518 boys were followed from 1-year school period. Maturational timing was self-assessed using the Tanner stage ratings (breast development for girls and pubic hair for boys). Early maturation was determined as the age bellow the median age within each gender SM group.

Results Girls with early maturation showed a statistically significant greater prevalence of overweight (WHO classification) compared to those without early maturation (23.7% vs 15.4; p=0.02) at baseline and similar results were found after 1-year follow-up. On the other hand weight gain during follow-up was not associated to maturation either calculated by stages of sexual maturation, according to Tanner staging or to early maturation, for girls and boys.

Conclusions The results suggest that at baseline and follow-up BMI was highly associated with SM for girls, but BMI increments during follow-up was unrelated to SM for both sexes suggesting a non causal effect of early age maturation on overweight. Also, there is no explanation for the gender effect.