The invention provides methods and compositions for modulating the expression, processing, post-translational modification, stability and/or activity of XBP-1 protein, or a protein in a signal transduction pathway involving XBP-I to treat dyslipidemias and steatosis disorders. The present invention also pertains to methods for identifying compounds that modulate the expression, processing, post-translational modification, and/or activity of XBP-I protein or a molecule in a signal transduction pathway involving XBP-1.