Soy is definitely not Paleo. It is full of phytates, which bind to minerals to prevent them being absorbed by the body. This can cause mineral deficiencies and digestive issues in a lot of people. Soy has also been shown to be mildly carcinogenic, and it can interfere with thyroid function. Add to all that the fact that soy (at least American soy) is almost always genetically modified (which comes with its own health risks, including a potentially higher incidence of cancer), and there is certainly nothing Paleo about soy.
The Benefits of Fermentation
Fermented soy is a slightly different story. Plenty of other fermented foods (such as sauerkraut and yogurt) come with enough health benefits to warrant at least a “maybe”. The fermentation process tends to get rid of at least some of the anti-nutrients and make certain nutrients more bioavailable. This is as true of soy as it is of other fermented foods.
The Nutritional Profile of Fermented Soy
Fermented soy sauce in particular has demonstrated some antioxidant properties and natto is actually the richest source of vitamin K2 found in food. Vitamin K2 is essential for maintaining healthy teeth and bones because it transports calcium out of the bloodstream to the bones and teeth. Without vitamin K, calcium just sits in our arteries, creating plaque and inflammation.
Choosing the Lesser of Two Evils
Fermented soy is still not Paleo-friendly, but if you just can’t resist that fermented soy sauce the next time you’re out for sushi, at least you can rest knowing it’s a much better option than unfermented soy. Just be sure to get the gluten-free soy sauce.
Mark Sisson gave his take on fermented soy here.