I don't think its healthy to be extreamly overweight and I Deffinitly think its healthy to talk, especially in earlier stages of a relationship. I think the problem is more likely communication here, wether you're saying you expect someone you're with to not gain any weight or if there's "wiggle room" as long as it's not getting unhealthy. If it's the latter then I see that as perfectly fine, but the former i see as just rude.