How can keeping a food journal help a person manage his or her weight?

Isabel wants to sign up with the online social network teenbook, which she heard about from her friends at school. the teenbook site asked isabel for some personal information to complete her registration. in addition to her full name, teenbook asked for the name of her school, the city where she lives, her age, and her favorite foods. what is the only information that isabel should give to best ensure her safety?