 The age of puberty for girls continues to decline. Last year, researchers published a study of more than 1,000 girls across the country and found a higher prevalence of onset of breast development among girls at ages 7 and 8 years old compared with those observed more than just a decade earlier. This has obvious psychosocial implications, but from a medical standpoint, the reason we're so concerned is that those who start developing at a younger age are at an increased risk of breast cancer later in life due to the increased estrogen exposure. For every year, puberty can be delayed. Risk of future breast cancer may drop 7%. A century ago, girls were starting their periods at around age 16, which may help explain why breast cancer is now such an epidemic. So what's contributing to this premature development? New study last year following 3,000 girls found the single most important dietary determinant was how much meat girls eat. Meat intake, measured at 3 and 7 years, was strongly positively associated with starting their period by 12 years, 8 months. And so the trends in age-at-menarchy in the West over the last century might reflect the trends in meat consumption. The second most powerful predictor was animal protein in general, so it wasn't just meat. The reason girls eating vegetarian have been found to develop more normally may also be influenced by their soy intake. Last year a group of researchers calculated that girls drinking just like 2 cups of soy milk a week start developing breasts an average 8 months later than those who drink hardly any. So I failed to have an effect, however, on timing of puberty in boys.