I think obesity is a real health condition that has real world causes - mental health problems, lack of access to healthy food, lack of access to healthy activities to name a few. Most of these can easily be attributed to our mode of production. I don't think you should shame anyone for being fat. It's not particularly helpful. Change the material conditions of people's lives and their lives will change.

That being said, I would encourage anyone who is able to lose weight if they are clinically obese, simply because it's not healthy. Healthy people are happier people, generally.