Meat, animal protein, and soymilk (soya milk) can affect premature breast development in girls.
Image thanks to Hamner_Fotos.
The age of puberty for girls continues to decline. Last year researchers published a study of more than a thousand girls across the country and found a “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 point of view, 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 a go, girls were starting their periods at around 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, so the trends in "age at menarche" 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 German researchers calculated that girls drinking just like two cups of soymilk a week developing breasts on average 8 months later than those who drank hardly any. Soy failed to have an effect, however, on timing in puberty in boys.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by Dianne Moore.
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Related videos on premature puberty include Hormones in Skim vs. Whole Milk and Xenoestrogens & Early Puberty. And there's more than a dozen videos on soy, including Soy & Breast Cancer and Soy & Breast Cancer Survival.
You may also be interested in my blog posts for more context on the topic: Breast Cancer and Diet, Soy and breast cancer: an update, How Much Soy Is Too Much?, and Why Are Children Starting Puberty Earlier?