Fu ふ (麩) is wheat gluten, often added to soups. It contains a lot of starch and is usually eaten in exchange for meat, especially in vegetarian temple food. It is also low of calories, low in fat and easy to digest. In Okinawa, it is mostly sold in dried, long tubes and is called 車麩 kurumu fu, although other forms are usually available in most grocery stores. Another bonus: it is CHEAP. So… of course it is popular(ish)!
Many people add it to miso soup to make it more filling.
Fu chanpuru フーチャンプルー is a popular dish in Okinawa. It is just like goya chanpuru, but with fu substituted for goya (or sometimes both are used!). Chanpuru is basically just a stir-fry.
So, when in Okinawa, try some fu. If you order fu chanpuru, don’t be surprised if the server taking you order looks at you funny… I do not think it is very popular with foreigners. We have been asked if we were ordering the correct thing before. Luckily I am able to reassure them that we know what it is and like it.