Does soy contain oestrogen?

Andrea put this soy suggestion to physiologist Sam Virtue...

Sam - As far as I can tell, no it doesn't. But soy contains some chemicals that mimic the body's own oestrogens called phytoestrogens. And the history of these is quite good. They were first observed in 1926, but we didn't actually know they could do anything until some farmers in the 1940s and 50s noticed that pastures of their sheep were not getting pregnant. And if you're a lamb farmer, that's something you want them to do. And they discovered that the red clover the sheep was eating was so rich in these phytoestrogens, they had effectively put their entire flock on the pill.

Chris - Are they effectively then molecules that look like oestrogen and work like oestrogen, but they're not oestrogen?

Sam - Exactly. And actually it gets a little complicated, because the oestrogens may have some potency on the oestrogen receptor, and the phytoestrogens, but it may not be as strong as our body's own. And so this means they can act to both promote oestrogen signalling in some people, or suppress it in others.

Chris - And so what would be the impact on things like diseases? Because we're worried about the role of hormones in some diseases like breast cancer.

Sam - Absolutely. And so this is why I mentioned the fact that they can be both promoting insulin signalling and blocking insulin signalling. So the evidence seems to be, from the majority of studies into soy itself, that it does not promote cancer and may even actually be protective of cancer in some individuals, but it's not certain.

Camilla - Does that mean that women trying to get pregnant shouldn't eat soy? Or were the sheep a different kind of experience?

Sam - I think that based on the stuff I read, you would need to eat a very, very large amount of soy for it to be an effective contraceptive.