Scientists probe why obese people may handle thirst differently

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

* INCLUSION CRITERIA: * Male. * Age 18-50 yrs to minimize hormonal influences on thirst perception in aging men. * BMI\<25 kg/m\^2 for the lean group and BMI \>=35 kg/m\^2 for obese group (but weigh less than 350 pounds to accommodate the DXA scanner) for the obese group. * Healthy, as determined by medical history and physical examination, without the exclusions listed below: EXCLUSION CRITERIA: History or Clinical Manifestation of: * Currently smoking * Any medications * Weight \<50kg (as the blood withdrawal limit would be exceeded) * Hemoglobin concentration \< 12mg/dl on screening labs * Type 1 or type 2 diabetes (according to World Health Organization diagnostic criteria (59)) * Endocrine disorders (Cushing's disease, pituitary diseases, hypo- or hyperthyroidism, diabetes insipidus, SIADH) * Hypertension as diagnosed and treated by an outside physician or by sitting blood pressure measurement, using an appropriate cuff, \>140/90 mmHg on two or more occasions * Fasting triglyceride concentrations \>= 500 mg/dl * Cardiovascular disease, including coronary heart disease, heart failure, arrhythmias and peripheral arterial disease * Liver disease, including cirrhosis, active hepatitis B or C and AST or ALT \>= 3x normal * Renal disease, as defined by serum creatinine concentrations \>= 1.5 mg/dl and / or proteinuria \>300 mg/day (200 (micro)g/min) * Central nervous system disease, including previous history of cerebrovascular accidents, dementia, and neurodegenerative disorders * Cancer requiring treatment in the past five years, except for non-melanoma skin cancers or cancers that have been clearly cured or, in the opinion of the investigator, carry an excellent prognosis * Infectious diseases such as active tuberculosis, HIV (by self report), chronic coccidioidomycoses or other chronic infections * Alcohol and/or current use of drugs (more than 2 drinks per day and regular use of drugs such as amphetamines, cocaine, heroin, or marijuana) * Psychiatric conditions or behaviors that would be incompatible with safe and successful participation in this study, including claustrophobia and eating disorders such as anorexia or bulimia nervosa All subjects will be fully informed of the aim, nature, and risks of the study prior to giving written informed consent. Subjects will also be specifically advised that the results of testing for drug usage will be filed in the medical record and would, therefore, be available as part of this record.