You are right about the cultural differences, my family and I are of Spanish-descent and we eat tons of white rice throughout our entire lives without any issues. My mom was the one who had a weight problem, but it could just be a result of unfortunate genetics and that's not her fault. Otherwise we eat lots of legumes, vegetables, fruits, home cooked meals, teas and coffees, and we were always "that thin family" in America. Americans just don't like to hear the simple truth that sometimes you just have to get down and busy in the kitchen and make your meals from scratch, especially for dinners where people like to get fork-happy and eat everything in sight. ;p
I am going to Thailand soon, where people there eat SO MUCH every day, yet are all very healthy and have low BMI in comparison to the average American. They get their seafood from catching themselves or getting someone else to do it for them, and then immediately cook them. Obviously the same with their fruits and veggies. I just think it all has to do with eating foods straight from the source, and it is now getting a trendy "organic" label when really its just straight up real food. I'll report back and see what differences their diets are compared to Western diets.
I think its so cool that you went to Japan! Was the language barrier tough? (I'm assuming you aren't Japanese, so forgive me if I am wrong!)