What's a good response to being asked if after gaining weight, gf/bf is less attractive?

Just wondering, because I was asked this before and I am pretty sure I gave the wrong answer. I'm not extremely superficial, but because I put in a lot of effort to be lean and healthy, I'd want my partner to do the same.

I wouldnt be going out searching for someone who doesn't meet my standards and then trying to change them, but I find a lack of discipline, responsibility, and hard work unattractive, which reflects in one's physical appearance. I never want kids and so pregnancy is essentially out of the question.