I wrote this blog entry about going gluten free in Japan http://from-japan-with-love.blogspot.com/2008/09/going-gluten-free-in-japan.html and I have received several emails with questions from people living in Japan so I thought I would give more info. Please remember that I'm not a doctor-I'm only passing on info that I have learned while living here.
First I've been asked to give the Japanese for certain words for those who can't read Japanese.
soy sauce (Kanji) 醤油 (しょう油)
soy sauce (hiragana) しょうゆ
In English, those who need to avoid gluten need to avoid wheat, barley, rye, oats (though there is debate about this one) but in Japanese they all use the same Kanji (for wheat).
What I've learned here is that you need to avoid ALL soy sauce in Japan-ALL soy sauce contains wheat in Japan. And MOST sauces in Japan, contain soy sauce-I have even found it in Italian salad dressings or soy sauce powder in lots of pre made powders (like the steak spice package that comes with many steaks), sauces etc. So...buying anything in a sauce is risky.
For those new to eating gluten free here veggies, meat, seafood, fruits, nuts (plain), dairy, tofu etc are safe....most other things are risky (even senbei has soy sauce). ALWAYS READ THE INGREDIENTS and even then, know that there will be times when you will eat some.
Ok...shopping! Shopping for gluten free food is easy thanks to a few online shops in Japan...easy but not cheap.
For wheat free tamari (like soy sauce) I buy it from http://store.alishan.jp/index.php?main_page=product_info&cPath=23_70&products_id=123
I also buy brown rice flour for when I make gluten free butter tart squares.
Most of the gluten free foods I buy from http://www.fbcusa.com/ . This online store has 2 food stores...one that has food already in Japan and can be delivered to your house in 5-7 days (called "the deli") and the other store- you order your food and it is delivered from the U.S in about 1 month (this is called "the general store") . Most of the gluten free food I order comes from the "general store" and therefore takes a month but it is worth it. When you enter the "general store" you can search for "gluten free" , "wheat free" or even "rice"(for rice pasta etc). I highly recommend the following:
Tinkyada pasta-this is the BEST brown rice pasta...people who need to eat rice pasta can't tell the difference! http://www.fbcusa.com/gs/index.php?main_page=advanced_search_result&search_in_description=0&keyword=tinkyada
Arrowhead mills brownie mix. http://www.fbcusa.com/gs/index.php?main_page=product_info&products_id=5047
Enviro Kidz cereal http://www.fbcusa.com/gs/index.php?main_page=advanced_search_result&search_in_description=0&keyword=enviro
Bob's Red mills pancake mix http://www.fbcusa.com/gs/index.php?main_page=product_info&products_id=11289
FBC also offers many other gluten free products.
Other online options
http://www.fbcexpress.com/ (a sister site to http://www.fbcusa.com/) has a shipping service. With this service you can order from American companies and have them ship to fbcexpress who will then ship them to you. I use this service a lot. For example... amazon.com offers many gluten free products in bulk size so if you know what you like, you can have amazon.com ship them to fbcexpress and then they will ship them to you. It is explained here http://www.fbcexpress.com/cart/customer/pages.php?pageid=11
I have also had food delivered from Canada http://www.elpeto.com/ They have THE BEST breads and other treats. I had them ship to fbcexpress and then they delivered to me. I would only do this in the winter. They do use a vacuum pack system for this type of mailing but I wouldn't risk it in the summer. Of course, ordering bread you would need a big freezer to keep it all in once you get it.
Supermarkets in Japan
Katakuriko (potato starch) is a great substitute for flour for coating chicken etc. Also almond flour/meal/powder (this can be found in the supermarket but it buying from bob's red mills and having it delivered via fbcexpress is cheaper if you use it a lot).
Pasta substitutes are "harusame" (green bean thread) and "bifun"which are Chinese noodles made from rice. Many supermarkets also have Vietnamese rice paper for "wraps".
Crackers-many senbei have soy sauce so read the ingredients. I love "happy turn" and there are some plain thin rice crackers which are ok but frankly I don't eat them because I love "happy turn" so much!
As I stated in my other blog post, eating out is difficult. I always carry a plastic bottle filled with my gluten free soy sauce. The 2 easiest things to eat out are sushi and yakiniku. Sushi is the easiest....order only sushi that doesn't have a sauce (avoid eel which almost always has a brown sauce) and just use your own soy sauce. Yakiniku is a bit tricky at first. You have to explain to the waitress not to put any sauce on the meat before they bring it to the table. You also need to make your own sauce. What I do is ask for garlic paste (niniku), red pepper flakes (tougarashi) and a small dish. I then put some soy sauce in the dish, add some garlic, red pepper and water from my cup to make a sauce. I LOVE it. And,if you are a regular at a yakiniku place they will get used to it. If a place gives you a hassle and asks why you don't want sauce etc just tell them (if you don't mind a little lie) " moshi shoyu ga tabemono ni haite itara zensouku ga demas" (if I eat something with soy sauce, I will have an asthma attack). This was actually true for me for many years and no matter how I tried to explain they would hassle me until I told them this so this is what I say even now if I am hassled. You can also substitute "shoyu" for "komugi" (means wheat) and tell them you will have an asthma attack if you eat anything with wheat.
I have also learned that most Japanese don't know much about food allergies in general but wheat allergies in particular are a new thing so asking a waiter if there is something in the food doesn't mean you will get the right answer. Most Japanese don't know that there is wheat in soy sauce so just be warned.
I'm sure that I'm forgetting something I wanted to mention. If you have any questions, please ask!
UPDATE- November 9th 2010 - I just updated some dead links.