Some Types of Soy May Be Beneficial to Girls
In their new book "The New Puberty," co-authors Dr. Louise Greenspan (a pediatric endocrinologist at Kaiser Permanente) and Dr Julianna Deardorff (an adolescent psychologist at University of California, Berkeley) focus on how the ever-decreasing age of puberty onset in girls. While eight years old has generally been considered the early end, more and more data shows they're actually starting at ages six and seven.
In the book, Greenspan and Deardorff try to answer the big question: Why? There are plenty of factors worth considering, everything from environment, to socioeconomics, to race (25 percent of African-American girls experience puberty at age 7, compared to only 10 percent of white girls). Embedded in all of those factors is the possibility that diet may have an extraordinary impact on early female puberty.
And this is where one of the duo's most intriguing findings comes in.
For years, the consumption of soy has been linked with all sorts of issues, from higher incidents of breast cancer, problems with female fertility, and overall issues with reproductive health. Science points the finger at isoflavons, a class of naturally-occurring organic compounds that mimic estrogen and, thusly, cause all sorts of complications in women.
However, the data in Greenspan and Deardorff's book suggests that rather than harmful, soy may actually be beneficial:
We did look at soy intake, both by asking the girls what they ate and also the measuring the levels in the urine. And we found preliminary data that suggests that soy is actually protective and that higher soy intake may lead to later puberty, even when controlling for the differences in the families where there was a lot of soy intake because obviously there are differences in families that are giving their kids a lot of tofu.
To be clear, they make it a point to focus on the fact that the soy isoflavons with the tangible benefit are found in natural sources, such as tofu, edamame, and soy milk. (Soy products found in energy bars and processed foods -- usually used to replace meat -- are still not recommended.) But as far as natural soy's concerned, have at it, kids of all ages:
We think that children should eat soy because that's when it trains their body to become resistant to estrogen.
This is a decent turn-around. While data tended to show soy as a possible harmful agent, at very worst it was seen as something that had no effect. But the shift to the idea that soy has a legitimate benefit in protecting women from developing breast cancer, among other things, is new. So, I emailed Greenspan and Deardorff a few questions for clarification:
How surprised were you by these findings, in lieu of previous findings of soy mimicking female hormones, which, as you put it, perhaps "demonized" the product?
Greenspan and Deardorff: We weren't completely surprised because there is evidence suggesting that women who eat soy as young girls have a lower risk of breast cancer. It's a complex issue, but the hypothesis is that exposure to the estrogen-like compounds, or phytoestrogens, in the soy may cause the body to become resistant to estrogen-like substances. There is likely a window during childhood development when this is true. This may lead to later onset of breast development, and in later life, this may lead to resistance to estrogen.
Does this mean that it's recommended for women to eat soy no matter the age? Or do they need to eat it during prepubescence in order to get the "protective" benefit?
Greenspan and Deardorff: Our data suggests that plant-based soy products are likely safe from a puberty point of view, and that eating these pre-pubertally may be protective against early puberty. There are different windows of susceptibility, and the downstream effect varies with the timing. We can comment on the effects in the younger girls. Older women is not our area of expertise.
