Prozac and the other SSRIs are  selective serotonin REuptake inhibitors:
they somehow make serotonin available longer in the synapse between two
neurons, so in effect they prolong the serotonin action rather than diminish
it. With obsessive-compulsive disorders and depression, the problem seems to
be a lack of serotonin, not excessive serotonin.

> These feelings are also responsible for other eating disorders such as
> bulimia and anorexia.  In many ways these feelings resemble drug
dependency
> and may be linked to serotinin uptake in the brain.  For this reason they
> are often treated with serotinin uptake inhibitors such as Prozac or
similar
> drugs.
>
> Of course limiting foods that cause excessive serotinin production such as
> grains, beans, potatoes milk and sugars may eliminate the problem.  >