One of my favorite romance author's Nora Roberts has done a few ex-fat protagonists and generally does it rather well. It's basic but well. One of her best was the female lead of Blood Brother's where she mentions her diet every time food comes up (because you have to think about it that much) but it's all done in a very positive way. She describes going on the diet as a point when she was done pitying herself and trying quick fixes and instead wanting to care for her body right. She's also funny and enjoyable and way more than a clothes size. It was actually very nice to read.