Body acceptance is one thing, body positivity is another. Obesity should not be celebrated, but it doesn't need constant ridicule either. As a fat woman, I already know I should lose weight, (but even my doctor only gives it a passing mention because I have mental health issues that are a higher priority). But even I, a fat woman, don't want to see a fat woman in her underwear on a billboard.
Maybe a jeans add. And the message shouldn't be about "my truth", just a "hey, these will fit you." I actually kind of like the current Old Navy campaign.