Once in a while for work reasons I have to eat at a Japanese restaurants. This is a food that I have always loved, but my recent paleo-awareness has made me much more cautious with many of their dishes. In terms of the soy-based products I have figured out this rule: the fermented soy based foods are O.K. (although strictly non paleo) so that having miso, natto or soy sauce is fine, or actually accepted, because, although soy has some antinutrients, the fermentation process destroys most of those toxins. On the contrary, non fermented soy based foods such as tofu should be rejected. Do you agree with my rule of thumb, and if you disagree, why?
Soy sauce, assuming it is actually fermented the traditional way, should actually be fine. The gluten and other nasty bits of the wheat are generally broken down in the fermentation. Of course, there is also the option of asking for a tamari soy sauce--which is just the fermented soy beans, not wheat and soy fermented. Then again, most places just use the crappy chemically made soy sauce. Then again, most Americans drown their fish in the soy sauce. Then again, most sushi places sell fish that probably needs to be dipped in soy sauce.
But seriously, Japanese food is pretty innocuous for the most part. I mean yeah, you could get tempura or katsu-don or something deep fried like that. But I'm not going to live my life in fear of eating an occasional bit of white rice with my fish and maybe a little dollop of soy sauce. And if I go out to a sushi place and I order the omakase and the chef puts something fried in front of me or something of unknown origin (which is often the case with a good sushi chef), I'm going to eat it and enjoy it. The world will not end because of one morsel, nor will my metabolism get totally out of whack. Which is all to say, if you have to eat at a Japanese restaurant, sashimi is great, sushi won't be the end of the world, and you might even be able to have some soba if you really want to freak all your paleo zealot friends out. Buckwheat is not, after all, a true cereal grain and isn't, as I understand, as nasty as wheat et al. Just avoid the fried stuff and maybe the spicy mayo based sauces and any wheat noodles and you're golden.
You might want to avoid the rice.
I've recently discovered that sushi rice is made with pretty sugary vinegar (That's why it tastes so good! Am I the last one to know this?), and it looks like much of the commercial sushi vinegar from Japan has both HFCS and MSG as ingredients. That rice may not be as innocuous as we'd like to believe :(
For those who really want to avoid soy, there's always Coconut Aminos as a soy sauce/tamari analog. I'm allergic to soy, so this is a pretty great thing for me.
I don't worry about the rice, it's pretty innocuous and I need some glycogen anyways :D
actually this is a great question because most paleo hacks say avoid all soy and i totally disagree. There is one soy product that I actually am OK with as a physician for a paleo dieter who is trying to lose weight. Sadly few can handle the taste or smell. That is natto. It is fermented soy beans that have unreal amounts of vitamin K2. There is very few sources that are better. I use it in patients who have serious metabolic bone disease or in those with very high calcium index scores with high cardiac (highly sensitive) CRP levels.
I get sushi once a week and always order a lot of aji (or saba), sake, and hokkigai (all wild). I'm not afraid of glucose, so I get them all nigiri. I also order natto just to gross out my GF and the people around me, but I eat that at home as well.
Edit: Yeah, I avoid the sauces and just put lots of wasabi on everything.