The Edible Woman uses character foils to create complex portraits of gender roles and the ways that they can influence the character's decisions. A literary foil is a character that is used to contrast another character, revealing parts of them that may not be explicitly obvious to the reader unless they are able to compare the character to someone else. Many of the novel's characters function as pairs, combining opposite characteristics and methods of embodying or refusing standard gender expectations.
Peter and Duncan are one of the most important pairs. Duncan is a foil for Peter; his non-conformity to standard masculinity accentuates just how much Peter is a typical, average man. Duncan is physically frail, and Marian often compares his body to that of a child. His body makes her uncomfortable and disconcerted. Peter, on the other hand, is strong and conventionally attractive. Marian, as well as several other characters, such as Clara, remark how Peter is "good-looking." Marian even states that he is "ordinariness raised to perfection," and that he has the kind of face that would appear in advertisements.
This difference in the two men's appearances is also a method of portraying Marian's differing relationship with them. Peter is conventionally attractive; a large part of why Marian is with Peter is because he is so ordinary and normal. Implicitly, she believes that it is what she is supposed to do. He fulfills her role as a conventional woman by being her conventional partner. Duncan, on the other hand, is a contrast to those gender norms. He doesn't fit the conventional gendered narrative. He isn't powerful, and doesn't try to control Marian in the same way that Peter does. Peter allows Marian to keep up her normal lifestyle, while Duncan serves as an escape by allowing her to experience someone who is uncomfortable and non-conforming. It is Peter who makes Marian feel strangled, because Peter represents repressive gender roles. With Duncan, Marian is free to be herself, and although Duncan doesn't show explicit love towards her, he does allow her to be herself. He often says what she is thinking, whereas Peter and Marian never appear to understand each other, nor do they ever communicate their true feelings to each other.
Another pair of characters that function as a contrasting pair is Marian and Ainsley. Marian is conservative: she dresses modestly, doesn't wear makeup, and is often silent in conversations, which becomes obvious when she attends an evening out with Len, Peter, and Ainsley, and feels talked over and hides under the bed without anyone noticing her absence for a long time. Ainsley, on the other hand, is loud and outspoken. She drinks heavily—while Marian is always trying to rigidly control her own drinking and dislikes being drunk—and seduces men, even going so far as to get Len drunk in order to lure him into having sex with her and impregnating her. Ainsley criticizes gender norms and self-identifies as a feminist, whereas Marian rarely comments on gender roles and approaches Ainsley with a sense of disapproval and skepticism. Ainsley's presence makes Marian's passivity all the more obvious to the reader.
There are several other pairs in the novel that depict different methods of being a woman or a man and conforming to the expectations attached to each gender. Clara and Ainsley are another pair, as are Joe and Peter. Len and Peter; the office virgins and Marian; and Duncan and his roommates all serve as literary foils for each other. And while every character offsets traits in another character, those portrayals are often complex. None of the characters, save for Peter, totally conform to the gender roles that are attached to being a man or a woman. Even though Duncan is somewhat "feminine" and contrasts Peter's masculinity, he also still behaves somewhat dismissively towards Marian's emotions and calls her "hysterical," which is a gendered term used by men to devalue women's emotions. Ainsley, despite her staunch feminism, marries and is pregnant at the end of the book, mirroring Clara despite functioning as her opposite for most of the novel. All of these contradictions are part of what makes it difficult for a reader to take away a single theme or message from The Edible Woman. The novel defies simple themes, and instead, explores the boundaries and intricacies of gender.