Scientists investigate the Body's energy burn to predict weight changes

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

* INCLUSION CRITERIA: * 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 EXCLUSION CRITERIA: * 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 * Liver disease (cirrhosis, active hepatitis B or C, and AST or ALT greater than or equal to 1.5 times normal) * Renal disease (serum creatinine concentrations greater than or equal to 1.5 mg/dl and/or overt proteinuria) * Central nervous system disease (cerebrovascular accidents, dementia, and neurodegenerative disorders) * Cancer requiring treatment in the past five years, except for non-melanoma skin cancers or cancers that have clearly been cured or in the opinion of the investigator carry an excellent prognosis (e.g., Stage 1 cervical cancer) * Alcohol (more than 3 drinks per day) and/or drug abuse (such as amphetamines, cocaine, heroin, or marijuana) * Current or past history of: bipolar disorder, schizophrenia or presence of psychotic symptoms, bulimia nervosa or anorexia nervosa, or current major depressive disorder * Pregnancy or lactation * Taking weight loss medications * Weight change of plus or minus 5% in the last 3 months Conditions not specifically mentioned above may serve as criteria for exclusion at the discretion of the investigators. Additionally, potential subjects might be excluded if they demonstrate a style of interpersonal relationships that would inhibit successful completion of the study.