Patient description: The patient is a 24-year-old man who has had type 1 diabetes for 11 years. He presents to the emergency room with hyperglycemia and concern for possible diabetic ketoacidosis after not taking his insulin for 3 days. The patient reports that he is currently homeless and has lost his supply of insulin, syringes, glucometer, and glucose testing supplies. The patient states that at the time of his initial diagnosis with type 1 diabetes he was hospitalized with a glucose value >1000 mg/dL. At the time, he was experiencing polyuria, polydipsia, and polyphagia. He reports that he has been on insulin since the time of his diagnosis, and he has never been prescribed oral agents for diabetes management. Most recently, he has been using insulin glargine 55 units once daily, and insulin aspart sliding scale 3 times daily. The patient has had previous episodes of diabetic ketoacidosis, for which he was hospitalized. With this episode of hyperglycemia, he is not experiencing any nausea, vomiting, or abdominal discomfort, and he appears well. His lab studies showed: A1c: 11.3% Creatinine: 0.9 mg/dL with eGFR >60 mL/min Aspartate aminotransferase (AST): 17 U/L Alanine aminotransferase (ALT): 14 U/L Beta-hydroxybutyrate: 0.1 mmol/L Bicarbonate: 25 mEq/L Anion

Clinical trial eligibility criteria: eligible ages (years): 18.0-60.0,  Obesity Diet Therapy Weight Loss Weight Gain Nutrition Therapy BMI greater than or equal to 27 kg/m(2) for the weight loss protocol but body weight less than 350 pounds to accommodate the DXA scanner BMI less than or equal to 24 kg/m(2) (and BMI greater than or equal to 18.5 kg/m(2) for the overfeeding protocols. A history of low BMI and difficulty gaining weight Age 18-60 years, to minimize potential co-morbid conditions which may indirectly affect EE. Minors under the age of 18 will be excluded because growth and pubertal issues are significant parameters that could affect our outcomes and also because the time requirements of the study are such that they would interfere with school schedules. Women who are post-menopausal will be excluded from the study as changes in their metabolism could affect the baseline measurements which are hypothesized to predict weight change Healthy, as determined by medical history, physical examination, and laboratory tests  Current smoking Type 2 diabetes (according to the World Health Organization diagnostic criteria) Impaired glucose tolerance (according to the World Health Organization diagnostic criteria) for those participating in the overfeeding study arms only Endocrine disorders (Cushing s Disease, pituitary disorders, and hypo and hyperthyroidism) Chronic pulmonary disorders, including chronic obstructive pulmonary disease that would limit ability to follow the protocol (investigator judgment) and obstructive sleep apnea syndrome; only subjects with mild or exercise-induced asthma on no medications or on beta-adrenergic agonists only (such as albuterol) will be allowed to enter the study (provided use of these agents is not required for one week before study entry) Cardiovascular diseases (coronary heart disease, heart failure, arrhythmias, and peripheral artery disease) Hypertension (blood pressure measurement higher than 140/90 mm Hg (overfeeding study) or 160/95 (weight loss study) on two or more occasions or use of anti-hypertensive medications) Diagnosed gastrointestinal diseases, including inflammatory bowel diseases (e.g., Crohn s disease and ulcerative colitis), malabsorption syndromes (e.g., celiac disease), gastric ulcer (active); only subjects with gastro-esophageal reflux will be allowed to enter the study Presence of a pacemaker or other implantable devices/shrapnel which may interfere with the MRI or CorTemp measurements