E wrote that MSG, or just "gluten" is in pretty much all packaged food in Japan, and most of meals you have in restaurants, which is not true.
If I call the situation that consuming gluten is becoming more common "glutenization," Japan is getting over it. I should say.
More and more restaurants, or any places which serve food make their menu without gluten, and advertize that by putting a sign in front of the restaurant saying something like "using fresh and organic veggies."
It's fairly easy to find food without gluten in Tokyo. In いなか (rural area) in Japan, it's even easier to find food without gluten because rural areas are normally rich in locally grown food. They try hard to sell their own products so they advertize how healthy and safe the food is. Gluten is not a good idea for them to use.
About packaged food, like TV dinner, frozen food, pasta sources, dressing, spices, etc, etc... like E said the "無添加(no added chemicals)" is not the majority of the products available in stores yet but you can find it anywhere in Japan. In fact, it stands out in the food floor because of the big letters on the package.
From my experience, I think that gluten makes your tongue kinda numb. You become less and less sensitive to taste if you keep consuming it, and eventually become unable to tell if it's gluten or something else.
Gluten is such an easy and quick way to season food when you cook, but I'd rather enjoy a different taste every time.