There is no consistent result in the relationship between obesity and timing of pubertal onset in boys .
Obesity may contribute to early onset of puberty in girls , while in boys , there is insufficient data .
This systematic review and meta- analysis examined the associations between obesity and puberty timing based on scientific evidence .
Earlier menarcheal age in Spanish girls is related with an increase in body mass index between pre-pubertal school age and adolescence.
BACKGROUND Higher body mass index ( BMI ) has been associated with earlier pubertal development . OBJECTIVE The aim of this longitudinal study was to determine menarcheal age in a Spanish cohort and to assess its association with anthropometric variables at birth , childhood and adolescence . We also analyse whether the tracking of weight between different ages could affect the timing of menarche . METHODS The sample population included 195 r and omly selected 6 - 8-year-old girls who participated in the baseline of the Four Provinces Study and in the follow-up of this study at 13 - 16 years old .  Anthropometrical variables were measured and BMI and BMI z-score were calculated . Information regarding birth weight and menarche was obtained by means of self-report question naire . RESULTS Correlation analysis showed a significant negative association of age at menarche with weight , BMI and BMI z-score in the baseline and follow-up groups but not with weight at birth . Fat mass at adolescence is related to a significantly earlier menarcheal age . When comparing weight categories , earliest menarcheal age is associated with an increase of BMI between 6 - 8-year-old and 13 - 16-year-old girls . CONCLUSION In our study , high weight in girls is associated with the earliest age at menarche . This becomes a major influence when weight gain occurs between pre-pubertal school age and adolescence
There is no consistent result in the relationship between obesity and timing of pubertal onset in boys .
Obesity may contribute to early onset of puberty in girls , while in boys , there is insufficient data .
This systematic review and meta- analysis examined the associations between obesity and puberty timing based on scientific evidence .