Soy has not been getting very good press recently. Last week the potential detrimental effects of soy consumption on male fertility aroused a storm of media interest and some choice headlines.

Some outlets and the Soya Association made the obvious observation that in many countries soy makes up a significant proportion of the diet but the populace still manages to reproduce somehow. Despite this, and the authors and fertility experts stressing that there is nothing to panic about, the press clearly care deeply about their readers’ sperm and panicked regardless.

At the root of these problems are the phytoestrogens – hormone-like compounds produced by plants – found in soy. They can be absorbed from the diet and can even cross the placenta and find their way into breast milk.

Moving from Woody Allen’s favourite to his second favourite organ, phytoestrogens are being implicated in developmental problems in the brain. Researchers at North Carolina State University are reporting that phytoestrogens consumed in soy-based foods can affect the brain development of rats with consequences for reproductive function.

The researchers gave newborn rats doses of two kinds of phytoestrogen, genistein and equol, and looked at effects of the diet on the rats’ oestrus cycle and also changes in the structure of the hypothalamus related to reproductive development.

The research found that both phytoestrogens caused disruption of the oestrus cycle – equivalent to early-onset menopause in humans – and that genistein induced early puberty. Furthermore they found reduced density of key neurons for reproductive function in the test rats’ brains.

The researchers say the big problem here is that changes to brain structure are irreversible and that humans and rats have similar circuitry in the parts of the brain responsible for controlling ovulation. Researcher Heather Patisaul says: “That part of the brain is organized by hormones during development – which is the neonatal stage for rats and during gestation for humans,” adding that, “if you understand what is broken, you may be able to treat it.”

Before we all enjoy another panic, it is worth bearing in mind that another recent study found no link between Chinese womens’ soy consumption (amongst other factors) and their age at menopause or the length of their reproductive span.

The research is online in Neurotoxicology this month.