That's because weight talk isn't a taboo in Japan where you have to constantly manouver through words in a socially acceptable manner to spare the fee-fees of the fatty. It's not offensive. Saying you've put on/lost weight has the same impact with saying ''Oh, you've changed your hair colour.'' Saying ''You're getting fat, it'd be better to take care of your body a little more.'' has the same impact as ''It's cold outside, you should wear more than a t-shirt.''  I fucking love it here.