Who are the main characters, and what is the main idea of the story?

The main character is Louise, "the fat girl", whose identity is tied up in issues of weight and eating. All the other characters essentially revolve around Louise such as her friend Carrie, her parents, and her husband Richard. 

The main idea of the story is an examination of one woman's drive to find love and acceptance both from the outside world and from herself. Through her constant struggles with weight and overeating, she finds her true identity and comes to terms with herself and her body issues.