My mom has been obese as long as I can remember, and even in the morbid category at one point (but had gastric bypass surgery and that brought her back down to simply obese.) However, me and my sister were never fat when we were < 18. That didn't happen until we got older. I was able to reverse it before it got too bad, but my sister just got out of control. I think in some cases, even if the obese parent manages to keep their kids a healthy weight, the kids still see how they eat and such and end up getting fat as an adult (particularly if emotional eating is the problem.)
That makes sense. I have many of the same habits as my father, both good and bad. It's pretty remarkable how influential our parents are on us, even those that chose to consciously reject or rebel are affected by the habits of their parents. I'm glad you were able to avoid obesity, I find that like any vice healthy eating is all about avoiding situations that present bad options. Something I've been bad at of late. I keep toiling with the idea of becoming a vegetarian. My wife is and I've dabbled in the past. Anyways, good luck to you and your mom and sister.