A 28-year-old woman with bipolar I disorder has been on olanzapine 15 mg/day for 10 months. She presents with a 6-month history of progressive weight gain (12 kg), increased appetite, and fasting blood glucose of 128 mg/dL. Her lipid panel shows total cholesterol 245 mg/dL and triglycerides 180 mg/dL. She is otherwise asymptomatic. What is the most appropriate next step in management?