Dieting is just as popular in Japan as it is in other countries, despite the low obesity rates and things there. Fad diets are very prevalent, as are a lot of dubious diet supplements (sapurimento). But if you look at traditional Japanese food, there are a lot of items that are naturally low in calories, carbs and glycemic indeces, high in fiber, and in some cases even have a lot of beneficial nutrients. These items are being looked at anew as weight loss aids in Japan, which is a great thing I think.
This week I'll describe some of these foods. They may seem odd to you if you're not Japanese (some more than others), but one thing is for sure - they have all been eaten for hundreds of years, if not longer, so they are likely not to kill you anyway. :)
Note: I've already described two foods here that are being touted nowadays as great diet foods: natto  (fermented soy beans), and okara  (the fibrous parts of the soy bean left over after making soy milk). I'll be talking a bit more about okara, but natto is such an 'acquired taste' that I'll let it be for now.
[Update:] Links to the entries: