The best answer to people like your uncle is to keep eating this way and lose a lot of weight. I have noticed that the more I lose, the fewer unsolicited lectures I get about low carbing not working and being unhealthy! In my experience, you can't win arguments with people like this -- all you do is get yourself upset -- so it is better to refuse to even get involved. I just refuse to reply, give them an icy stare, and either let silence hang in the air or change the subject. It generally works. If they are trying to make me feel uncomfortable, I have no problem with doing the same thing to them.

I think that the tendency to gain weight, and the tendency to have blood sugar problems that lead to weight gain, are probably genetic. However, if we can figure out what are genetic triggers are (for me, clearly carbohydrates) we can get past them. Your parents may have been in the situation I was in for decades -- not understanding what made them fat. The same diet may well not have made your uncle fat if his genetic make-up is different. We all know thin people who eat carbs and junk food all day. They probably just got dealt a different genetic hand than we did.