This article draws on qualitative research inside one UK secular commercial weight loss group to show how ancient Christian suspicions of appetite and pleasure resurface in this group's language of "Syn." Following ancient Christian representations of sin, members assume that Syn depicts disorder and that fat is a visible sign of a body which has fallen out of place. Syn, though, is ambiguous, utilizing ancient theological meanings to discipline fat while containing within it the power to resist the very borders which hold women's bodies and fat in place. Syn thus signals both the dangers and powers of disordered eating.