Why Do the Textbook Authors Describe Dieters Who Have Fallen

Why do the textbook authors describe dieters who have fallen to a weight below their set point as being engaged in a "battle against themselves"?

A) Their hypothalamus has been damaged.
B) They have an emotional conflict between their desire to diet and their desire to eat.
C) Their brains are working against them to get them back to their "set point."
D) What they want for themselves and what society tells them is attractive are two different things.