BAHAHAHAHAHA I knew it was gonna be this!
I would rather not hear commentary from a significant other, personally. I'm not going to suddenly wake up having gained 20+ pounds without noticing. I'm incredibly neurotic about this stuff - I would notice if I gained 2 pounds, let alone enough to "make a difference."
Think about when your SOs gained weight or lost some. My dude gained 5-10 lbs when he got a new job - I barely noticed, maybe a little, but I would
never say anything unless he was obviously undergoing some kind of personal meltdown and reverting to piles of Chinese takeout and secretly eating meals between meals. He noticed he had gained and started packing smaller lunches and started an exercise routine in the mornings before work and lost it and then some.