Effect of Fasting on Ghrelin and Growth Hormone in Healthy Young and Older Adults

Inclusion Criteria: Healthy young (ages 18-30) and older (ages \> 60) men and women with a body mass index (BMI) of \<35 kg/m2. Young and older subjects will be matched for BMI. Exclusion Criteria: 1. A history of coronary artery disease, congestive heart failure, peripheral vascular disease, diabetes mellitus, significant hypertension (BP \>180 systolic or \>100 diastolic at rest); renal, hepatic, pulmonary disease; untreated hypothyroidism, untreated hyperthyroidism; history of seizure disorder; history of malignancy (other than some skin cancers), history of active chronic infections (e.g., HIV, tuberculosis): abnormal screening laboratory tests. This information will be obtained through the use of screening labs, history and physical exam and the medical record. See the GCRC protocol for details of the labs. 2. Hematocrit \< 41% men, \< 38% women 3. History of daily tobacco use within past 3 months 4. Chronic alcohol abuse 5. Recent weight change of \> 10 pounds in last 3 months 6. Strenuous exercise for average of more than 60 min/day 7. Investigational drug within past 6 weeks 8. Any history of major psychosis, severe depression, anorexia nervosa 9. Transmeridian travel within 2 weeks prior to or during study -