Undesirable changes in body weight, blood sugar control, type 2 diabetes, and blood lipids occur more commonly in people who have schizophrenia than in people without psychiatric conditions. Although differences in glucose regulation were first reported in schizophrenia before the use of antipsychotic medications, antipsychotic treatment may contribute to these problems, though just how this happens is not understood. This study proposes to use a doubly-labeled water (DLW) method to measure the degree to which weight gain (fat mass) is due to increased appetite, decreased physical activity from being tired and sleepy, or some combination of both. Doubly-labeled water contains stable isotopes (non-radioactive forms) of the hydrogen and oxygen that make up all water, isotopes that will be slowly passed out through the urine after participants drink DLW. The number of hydrogen and oxygen isotopes found in the urine samples will tell us how many calories the participant's body has been using.