Does anyone have any clue what it is specifically in their genetics that makes them thin in general?
Most of my Asian friends (not all, but a higher percentage than any other group) are very thin. I'm black and I don't think I could get that thin to save my life. And I kind of want to, I like the very thin look they have. But it wouldn't even look the same on my body type though.
Some of the other answerers have said 50% is genetics... in this case, I think genes have much more to do with it than that, maybe 70%-90%. If you compare your wrist with the wrist of one of your Asian friends, I'd bet that hers looks tiny. And because wrists don't gain weight, the size completely depends on the size of that person's bones. A person with an especially small wrist (like many Asian woman have) will always be naturally smaller than someone with naturally larger, or thicker, bones.
Diet and culture has a lot to do with it, too, but there are some ethnicities that have a genuine predisposition to be very small, no matter what they do or eat. Trying to match the skinniess of your Asian friends is probably impossible for you because it is completely *unnatural* for your body type. But what's wrong with that? Your body comes along with its own advantages and hot spots that no one else has, too!
Genetics partly. Asian wome on average have more eostrogen than women of other races, which leads to smaller bone structure. But really it's mainly habits and diet. A lot of Asian women do gain weight to when they move to America, they just traditionally have a much healthier diet.
Also in a lot of Asian countries thin women have been ideal for way longer than they have been here. And in a time where women have close to no nights they were obligted to fit that ideal, then it just became tradition. But ask Asian friends, Asian parents tend to be a lot more critical on their daughters weight.
That being said, they're getting bigger too, so big that japan has introduced a "fat tax"