Even if you are overweight (which I’ve no idea if you are or not?!) and he is aiming to address that, he should be approaching it in a kind and constructive way.

When you disagree with him about other things, how is his communication style? Is he dismissive/rude/unhelpful? If so, this is a bigger issue on his part and unless he is willing to acknowledge and resolve it then you will struggle to get anywhere with fixing this.