So we all know that soy is unpaleo, but we also know that fermenting foods is generally good. WAPers argue that fermenting can even make grains healthy. So where on the spectrum from poison to healthful do soy products like tempeh, miso and natto fall?
Personally, I'm particularly interested in miso, so I have some unpasteurised, fermented stuff lying about. Natto is also interesting given its ludicrously high levels of vitamin K2, though it seems impossible to get hold of.
I wouldn't go near tofu or soymilk or anything like that, but I do a lot of at-home Chinese cooking and I often use fermented soy ingredients (good soy sauce, fermented black soybeans). Fermenting mitigates most of the soy nasties, enough that I think they're fine if you treat them as condiments.
I generally tell my clients to keep away from soy even though it has become one of America's foods of choice. I do know that the only way I would ingest soy is if it were fermented. The eastern way of eating soy was/is fermented and in very small quantities. It is only through marketing and lobbying that soy has entered the American diet. Pigs can only eat so much of it so it was sold to us as a "health" food...don't buy it!
I use it in some recipes in teeny tiny quantities. I make miso glazed salmon quite often. I also sometimes cook Korean recipes that use Ssäamjang, another fermented soy paste. I view it as a mildly probiotic flavoring rather than a part of my diet. I can't give up being a foodie!
It's funny because many paleos indulge in far worse borderline foods like chocolate or the omega-6 powerhouses olive oil and tahini. I classify fermented soy as healthier than those things, but definitely not paleo.
Supposedly the goitrogens persist through the fermentation process. I was eating natto every time I got sushi until I realized that it was blocking the iodine from the meal, of which there would be more than usual. I was also eating it frequently at home, but I've since cut it all out and get my K-2 from liver and butter instead.
The K2 in Natto is MK-7, the bacterial form. MK-4 is the form produced by animals, for example, in grass fed butter. The MK-4 form may be more usable/absorb-able. To me, that removes another reason for considering soy.