I found this article and thought, why reinvent the wheel? The first couple of paragraphs, including the hand-dandy linked table of contents, is pasted below. Please have a peek and if you are interested you can jump over to the extremely well written article on the topic over at www.legalnomads.com.
“When I said I was heading to Japan via a 15-day repositioning cruise across the Pacific Ocean, most of my friends and family wanted to know what I would do at sea for 8 days straight. What I wanted to know, however, was what I would eat as a celiac in Japan, a country with quite a lot of wheat in its current diet. This gluten free Japan post is the summary of not only what I ate, but also the research surrounding some of the foods in the country and a translation card in Japanese to navigate Japan with less fear.
When people think of Japan, they often assume it will be easy for celiacs. After all, there is an abundance of rice, and sushi is generally thought of as free of gluten. Unfortunately Japanese food is also rife with soy sauce (which has wheat), barley, and wheat flour, and even basic sushi rice sometimes contains a vinegar that blends barley malt with rice vinegar, causing distress for celiacs.
Historically it was rice and not wheat that was grown and used in cooking throughout Japan. While wheat was consumed in small quantities, it wasn’t the prevalent filler that it is today. Wheat imports have grown steadily since the 1950s, and as Slate’s Nadia Arumugam writes, a good part of why is due to an aggressive advertising campaign and subsidized wheat-filled lunches provided to Japan by the US Government after World War II.
These days, with instant ramen noodles, wheat-filled sweet buns and custard treats, and soy sauce that now contains wheat, it is incredibly difficult to avoid gluten.”
Please note there is MUCH more information if you jump to the source.
Photo by Indil77 (File:Gluten free SVG.svg) [CC0], via Wikimedia Commons