Protocol Number: 04-DK-0061
African-Americans will be enrolled at NIH, and both Caucasians and African-Americans will be studied at the Mayo Clinic. Candidates must be between 18 and 49 years of age. Equal numbers of normal weight, overweight, and obese individuals will be recruited. Candidates will be screened with a physical examination, electrocardiogram, and blood tests, and will be interviewed about diet, exercise, medical history, family, and employment. Participants will undergo the following procedures on an outpatient basis: -2-week weight maintenance diet and clinic visits on 10 consecutive weekdays: A dietitian will design a diet for each participant that is geared to maintaining the same weight throughout the study so that the rate the body uses calories remains constant. For 2 weeks (except weekends), study subjects come to the clinic in the morning to be weighed, eat breakfast, and receive carry out food for the rest of the day (and on Fridays, for the weekend). -Computed tomography (CT) and dual energy x-ray absorptiometry (DEXA) scans: On one dietary visit, subjects have a CT scan of the abdomen to see how much fat is deposited there and a DEXA scan to measure total body fat. For each scan, the subject lies on the back on a table for about 15 or 20 minutes. After the 2-week diet, subjects are hospitalized for 2 days for the following tests: -REE and measurement of fatty acid flux: These tests are done twice on consecutive days, because the measurements vary from day to day in the same person. Two readings give a more precise picture of the rate the body uses calories when at rest and the rate that fat travels through the blood. For each procedure, the subject eats dinner at 6:00 p.m., after which a small plastic tube is placed through a needle into an arm vein. The next morning, two stable isotopes (naturally occurring forms of chemical elements such as hydrogen or carbon that are slightly heavier than the more common forms of the same element) are infused into the vein. A second tube is placed in a vein in the other arm, and the hand of that arm is placed in a hand warmer (a clear plastic box with warm air). A blood sample is taken from the second tube every 10 minutes over a 1-hour period, for a total of five samples. For the last 30 minutes of the test, the participant breathes normally under a clear plastic hood, in order to measure REE. The tubes are then removed and the participant eats breakfast. -Oral glucose tolerance test (OGTT): On the second morning of the hospitalization when the REE measurement is completed, subjects have an OGTT. For this test, the subject drinks a sugary solution. Blood samples are taken every 30 minutes for 3 hours. When the test is finished, the subject eats breakfast, has his or her vital signs checked, and is discharged.
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