Marc Joseph Nutrition - Blog

A small recent study took a look at how soy isoflavone levels changed in infants fed soy isoflavone-containing breast milk, in infants fed tofu, and in mothers drinking a soy protein beverage.

The researchers found that soy isoflavone levels increased significantly in mothers consuming a single soy protein beverage for 2 to 4 days, and by even higher amounts in the infants exposed to breast milk from these mothers. The increase in soy isoflavone levels in tofu-fed infants was even greater — more than ten times greater.

To the extent that the soy isoflavones have an estrogenic effect, these results suggest that nursing mothers and infants may want to avoid/minimize the consumption of soy products.

The estrogenic equivalent of five birth control pills.

That’s the amount calculated by one toxicologist of what an infant exclusively fed soy formula* is exposed to each day.

* Approximately 25% of infants in the U.S. are raised on soy formula.

And that’s just one example of the potential negative effects of sustained high-level intake of soy products. Elevated levels of metals such as manganese and aluminum are also concerns.

Additionally, Israeli and French public health agencies have recently issued warnings about eating high amounts of soy, especially by young children.

Two recent articles provide good overviews of the potential issues regarding soy in our food supply:

1. Should We Worry About Soya in Our Food?
2. Too Much of a Good Thing?

They’re both well-written and worth reading if soy is currently a regular part of your diet or you’re considering making it so.

My take is that the evidence on soy isoflavones is inconclusive. I’m
skeptical of many of the pro-soy studies given their funding sources. There seems to be enough research evidence to raise significant and reasonable questions.

For an unbiased look at the research evidence for soy in preventing and treating disease, see this link.

Whether it’s heart disease, prostate cancer, osteoporosis, or
menopause issues, there seem to be other reasonable and
effective diet and supplement alternatives that provide benefits
without the potential risks associated with soy isoflavones.