Could a cooler room help you burn more calories? scientists investigate.

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

* INCLUSION CRITERIA: * Generally healthy. * Males between the age greater than or equal to 18 -35 years or between 55-75 years, male orand females between the age 18-35 years. * Self-reported non-Hispanic and non-Latino Caucasian and African-Americans * Written informed consent. EXCLUSION CRITERIA: * Hypo- or hyper-thyroid (history or TSH \>5.0\<0.4 miU/L) * Psychological conditions,such as (but not limited to) claustrophobia, clinical depression, bipolar disorders, that would be incompatible with safe and successful participation in this study * Weight change \>5% in the past 6 months or a trained athlete Blood pressure greater than 140/90 mmHg or current antihypertensive therapy * History of cardiovascular disease * BMI \<18.5, between 25.1-29.9, and \>40 Kg/m(2) * Diabetes mellitus (fasting serum glucose \> 126 mg/dL) * Liver disease or ALT serum level greater than two times the laboratory upper limit of normal * Iron deficiency (Ferritin \< 30 mcg/L males, \< 15 mcg/L females) * Abnormal kidney function (eGFR\<60 ml/min/1.73m(2)) * History of illicit drug or alcohol abuse within the last 5 years; current use of drugs (by history) or alcohol (CAGE greater than or equal to 2) * Current use of medications/dietary supplements/alternative therapies known to alter energy metabolism * Pregnancy/breastfeeding/hormonal contraception or childbirth within the last year * Perimenopausal (as self-described within two years from onset of amenorrhea or current complaints of hot flashes) * For pre-menopausal women, irregular periods or polycystic ovarian disease * Current smoker or user of tobacco products * Metal implant that prevents subject from being in a MRI scanner. All subjects will be fully informed of the aims, nature, and risks of the study prior to giving written informed consent.