Gaining

Who's come out to their family about their kink, and how did they react?

My family only knows that I'm ok with my wife being overweight and that I actually find her size attractive. But, they know nothing about me wanting to gain on purpose, my wife gaining on purpose at times, or anything else like that. They will never know either. Certain things I think are private. Sex life and Kinks being one of them. My family is also very against fat. So I don't think they could understand my views even if I told them. But, this just me.

My family also only knows I like overweight women. I can't see weight-gain kinks being accepted.

Yup! I've seen intentional weight gain and feederism mentioned from time to time on places like Reddit and YouTube. Needless to say, the reaction was all negative.
Just like most Kinks and fetishes, other people won't understand. I also think it would be quite difficult to explain it to someone. To give them reasons why we think and feel this way. As it goes against regular society. Anyway, yeah, I really think it's something to keep between significant others and like minded people.