The last time United States audiences heard of French writer/director Catherine Breillat (To Mathieu) was when she released Romance, a pretentious porno disguised as an art house film. This time around, she still sets out to shock the audience, but there is a little more substance behind her lurid imagery. Fat Girl is about the sexual awakening of two very different sisters; twelve-year-old Anais (Anais Reboux) and fifteen-year-old Elena (Roxane Mesquida, Gaia, The School of Flesh). The two are on vacation with their parents and are looking to lose their virginity. To them, sexual experience is good and attracts men. Men do no want inexperienced women, and do not like sleeping with virgins.

Elena wants to seduce a man so she can begin her life. She is young and extremely attractive, and sets her sights on Italian law student Fernando (Libero De Rienzo, Asini, La Via Delgi Angeli). He wants to sleep with her and begins saying all the right things to get into her pants. It's a dangerous game of cat and mouse, with both sides trying to manipulate the other for their own ends. Anais has the opposite mentality. She wants to save herself for somebody she love and who reciprocates the feeling. Nevertheless, pretending to sleep in the same room as Elena and Fernando make out is slowly changing her mind. Anais is fat, so boys usually ignore her. Elena and Anais have a strange sisterly relationship. Elena mercilessly teases Anais about her weight, but then has dramatic mood swings and cares for her sister. Their parents are blind to the troubles their daughters are going through.

The first half of Fat Girl is about Elena and Fernando. Breillat is demonstrating how destructive one's tendencies can be. However, she goes about this using sensationalistic methods designed to produce horrified reactions rather than through any sense of a plot. The scenes with Elena and Fernando fall just shy of pornographic, and this serves no purpose at all. When Breillat finally decides to focus on Elena, she finally manages to get her message across. She shows Anais' inner struggle to reconcile the desires of her heart with those of her mind. Nevertheless, Breillat seriously falters at the end of the movie, putting in an arbitrary resolution that again, does nothing but shocks the viewer. Although it does provide some closure for Anais, it does so at the expense of other characters and cheapens the effort that Anais went through.