What is the mechanism for aripiprazole's effect on reducing olanzapine-associated obesity?

We read with great interest Henderson and colleagues’ paper in your journal (2009; 29:165–169), which reported that aripiprazole reduced olanzapine-induced overweight/obesity and hyperlipidemia in a 10-week placebo-controlled double-blind crossover study. This and their previous studies, provide a new way for controlling olanzapine- and clozapine-induced weight gain/obesity using another atypical antipsychotic, even without reducing the original olanzapine and clozapine doses, which is important particularly for treatment of refractory schizophrenia patients. ....