Have you ever seen that picture of two people looking at a number drawn on the floor?
One person is seeing a 6 and the other is seeing a 9. And they are both arguing about who's right.
This is my feeling about this whole thread.
OP, to you the words 'heavy' and 'fat' hold a very negative connotation. You woudn't use those words because you're struggling emotionally with your weight. You somehow believe that your weight defines your beauty or your worth. So when someone states the obvious and tells you that you're fat, you feel hurt. But that's just your interpretation of the word. Fat, to you, is a degrading word. It's not. It's just an adjective.
Is it possible that for your husband, the words 'heavy' and 'fat' don't hold the same negative value? And that to him, they are just descriptive words, used to state an observable fact? That they in no way diminish his image of you, your beauty or your worth? That he didn't use them to tear you down, but just to acknowledge what's happening?
He even tried to adapt. He used the word heavy (which, as being overweight myself I would actually prefer). He then adapted to another word, as per your preference. So maybe, since he's willing to be mindful of your sensitivities, you could just tell him what words you'd like him to use going forward?