Yes, the Japanese have been self-sufficient, but at a dire cost. That's why the Chinese always referred to them as "Evil Dwarves" ~ at the same time the Japanese avoided 4 foot long Broad Swords!
I have witnessed the joy on the face of a Japanese-American lady as she realized that she actually had some relatives who exceeded 6 foot!
Yes, not all Japanese are short people ~ but for most of their history since the Medieval Warm Period, they have been!
In modern times they import a vast percentage of their food ~ particularly grains other than rice from the United States.
Of course, the limited supply of Japanese rice was the first to get bought up at the markets, even though it was premium priced. The California rice followed not long afterward. Then the Australian rice. The Thai rice was hard to move. By the following spring, they were clearing out 5 kg bags of the stuff for 300 yen (versus 1200 or 1300 yen for the then non-existent local stuff). I bought some, took it home and had my wife fix it with the normal meal. The kids took a couple of bites and then refused to eat it.
Fast forward to 2002, when we moved back to the United States, I bought some of that normal white bread at the market. Same reaction from the kids.