If your partner/DH etc was overweight (not huge amounts, just enough to grow a little tummy and a little double chin) would you tell them? I mean if you loved them anyway but perhaps prefered them slim?
Obviously there is the health issue and I suppose you could put it that way.
What if they didn't want to do anything about it or did but didn't actually make much effort?
What if you didn't really fancy them so much when a bit chubbier? Would you tell them?