This is true -- A few years ago I ran into an old acquaintance several times, seeing him where we both worked (a college). I had known him back in the 80s and I had gained a lot of weight while he is one of those genetically skinny guys so no weight gain. Anyway I was in an antique mall and the owner and I both knew this guy and I was mentioning him. The owner (another really skinny guy) said (of my aquaintance) "he's really concerned about your health." That bothered me as I knew the translation "Wow you're really fat." Also I thought it was rude telling the antique mall guy that. I answered that I was puzzled becuase I felt fine. But I knew why he said it and I didn't appreciate it. Plus both the aquaintance and the antique mall owner both smoke so maybe I had better have worried about their health.

The point I'm making is it can be real rude just to go up to someone and say that. It's different if the subject comes up in a conversation and the person is curous about healthy eating plans.