Sometimes those messages are poorly given out, but there is also a problem with this "love myself no matter what" idea. Yes, we should love ourselves, especially for the good that we bring into the world. But, we can still love ourselves, yet, strive to do better. That's the message that needs to be put out there.
I loved my parents while they were alive, but I did not love their life choices of drinking and smoking. It eventually killed them. If one is over weight and eating poorly, they may also be killing themselves. That does not mean they can't love themselves, but it should encourage them to stop any habits that are unhealthy. Carrying a little extra weight or not having the perfect body shape is not the issue here. It's being overly heavy and unfit enough that one KNOWS they are damaging their body and lifestyle.
So, whether or not one can "not love someone they do not know" isn't what one needs to focus on. It's, "am I taking care of this person that I know and love?" That's the question we need to answer. Keep the Faith