Patient description: A 46-year-old Asian woman with MDD complains of persistent feelings of sadness and loss of interest in daily activities. She states that her mood is still depressed most of the days. She complains of loss of energy and feelings of worthlessness nearly every day. She is on anti-depressants for the past 6 months, but the symptoms are still present. She does not drink alcohol or smoke. She used to exercise every day for at least 30 min., but she doesn't have enough energy to do so for the past 3 weeks. She also has some digestive issues recently. She is married and has 4 children. She is menopausal. Her husband was diagnosed with colon cancer a year ago and is undergoing chemotherapy. Her past medical history is unremarkable. Her family history is negative for any psychologic problems. Her HAM-D score is 20.

Clinical trial eligibility criteria: eligible ages (years): 18.0-50.0,  Healthy Healthy Volunteers Adults age 18-50 years, male and female 2. Weight stable (less than or equal to 5 % over past 6 months) as determined by volunteer report 3. Body mass index (BMI) greater that or equal to 20kg/m2 4. Body weight greater than or equal to 53 kg 5. Able to complete daily bouts of stationary cycling at a moderate rate and intensity with a HR equal to or greater than 0.3(SqrRoot) (220-age-HRrest)+HRrest but not exceeding 0.4(SqrRoot) (220-age-HRrest)+HRrest and no signs of arrhythmia  Evidence of metabolic or cardiovascular disease, or disease that may influence metabolism (e.g. cancer, diabetes, thyroid disease) 2. Taking any prescription medication or other drug that may influence metabolism (e.g. diet/weight-loss medication, asthma medication, blood pressure medication, psychiatric medications, corticosteroids, or other medications at the discretion of the PI and/or study team) 3. Positive pregnancy test or lactation as determined by volunteer report (women only) 4. Participating in a regular exercise program (> 2h/week of vigorous activity) as determined by volunteer report 5. Hematocrit <37% (women only) 6. Hematocrit < 40% (men only) 7. Caffeine consumption > 300 mg/day as determined by volunteer report 8. Regular use of alcohol (> 2 drinks per day), tobacco (smoking or chewing) amphetamines, cocaine, heroin, or marijuana over past 6 months as determined by volunteer report 9. Psychological conditions such as (but not limited to) eating disorders, claustrophobia, clinical depression, bipolar disorders, that would be incompatible with safe and successful participation in this study, as determined by investigators. 1. Past or present history of eating disorders as determined by volunteer report 2. Past or present history of claustrophobia since part of the protocol will involve being confined to a small room for whole-body indirect calorimetry and being in an MRI scanner for liver fat measures 10. Implants, devices, or foreign objects implanted in the body that interfere with the Magnetic Resonance procedures 11. Volunteers with strict dietary concerns (e.g. vegetarian or kosher diet, food allergies) 12. Volunteers unwilling or unable to give informed consent 13. Non-English speakers due to unavailability of required questionnaires in other languages