So from the comment on my previous post i see my words were not as clear to others as they were to me. my apologies. i sometimes write with the understanding that everyone knows what i am talking about…LOL
Anyway, I have found this theory of reactance to be very interesting. The link will take you to a wiki page that delves further into reactance from a psychological standpoint.
To explain a bit more than my first post…Psychological reactance occurs in response to threats to perceived behavioral freedoms  . The fear of loss of further freedoms can spark this arousal and motivate reestablishing the threatened freedom. Because this motivational state is a result of the perceived reduction of one’s freedom of action, it is considered a counterforce, and thus is called “psychological reactance.”
There are four main points to psychological reactance: 1. perceived freedom, 2. threat to freedom, 3. reactance, and 4. restoration of freedom (my diet scenario clarified, hopefully).
Hopefully this clarifies my thinking a bit more.