Women's motivation to lose weight is to get the recognition of men, especially the recognition and praise of their loved ones.
If you always show dissatisfaction with her current figure in words, eyes and even some behaviors, she will definitely keep it in mind and use it as a reason and motivation to lose weight.
"Fat and thin" shows that the man caters to men, which also shows that she loves you very much, and at the same time shows that you have met a woman who likes to pursue beauty. This is not a bad thing, but enough is enough.
I hope you are happy.