I don't think it's fair to judge diets looking through the Westernized lens. The habits of Asians back home are probably quite different from those of immigrants, and there's probably a wide range among immigrants (and 2nd/3rd+ generation) in terms of similarity to diet back home vs once they're assimilating. Of course, there are a myriad of diets, too. Urban vs rural, impoverished vs more affluent, just like everywhere else. These conversations get borderline-racist and based on stereotypes.
I'm pretty sure there's not as much soy consumed in Asia as you'd think from stereotypes. Most of it is fermented in the form of soy sauce, or small quantities of tofu here and there. This was definitely the case for my Malaysian room mate. They're not packing away the Yves veggie dogs, I'm pretty sure.
They also aren't ruining their metabolism with breakfast cereal and cola (yet), so the rice and noodles aren't killing them (yet.) It will, as Western culture permeates. It's already obvious in 2nd/3rd+ generations over here.
In the case of the Japanese, they seem to "respect" food and meals more. It's rude to mindlessly eat while you're walking down the street, in class, traveling, etc. Gee, I'd love to see that here. You eat in your house at your table, in the lunch room at school/work, on the premises at which you purchased the food/drink, in your car if you park somewhere, and nowhere else. I bet people visiting from Japan must think we're gross for needing garbage cans on every street corner so that people can throw away their food packages, because they can't get from point A to point B without eating. They must sit on public transportation, surrounded by people eating and drinking, thinking we're animals. Imagine the dent we'd put in the obesity crisis with that change in etiquette alone.
BTW, I don't know where the OP lives, but I marvel at the health of the older people in Toronto's Chinatown. Not that these observations are worth much, of course. By definition, you're only seeing people who are healthy enough to go out in public on their own. There's no way of knowing the ratio of healthy to unhealthy.