Participant Testing
The following is a list of tests that will be performed throughout the study period. You will receive a more specified schedule when you come to the center for screening.

Oral Glucose Tolerance Test (OGTT): This test takes approximately 2 hours and will be completed during your inpatient stays. The OGTT is done to measure your body's response to glucose (sugar). Before you eat breakfast you will drink a glucose beverage and have blood drawn every 30 minutes for 2 hours. An IV tube will be placed in your arm and blood will be collected through this tube. You will be asked to consume a high carbohydrate diet for 3 days prior to testing.

VO² max test: This test will take approximately 20 minutes and measures your aerobic fitness. To perform this test you will wear a mouthpiece, noseclip and heart rate monitor. Following a 5-minute warm-up, you will be asked to run at a comfortable pace and grade that will progressively get harder each minute until you are winded and unable to continue.

Resting metabolic rate testing: This test takes 1 hour and will be complete during your inpatient stay. You will be asked to lie in a bed. We will put a clear plastic bubble over your head and seal it around your pillow. The hood is ventilated with fresh room air. From this we measure how much oxygen you breathe in and how much carbon dioxide you breathe out, which allows us to measure how many calories you burn while resting.

Muscle strength and endurance: This test will take 20 minutes. You will be asked to sit in a special chair called a Cybex. Your strength will be measured by extending and flexing your lower leg 5 times using maximal effort. Endurance will be measured by extending and flexing your leg 30 times at a faster rate using a sub-maximal effort.

Fat and Muscle biopsies: (optional) This will take approximately 1 hour and is used to sample fat cells from underneath the skin of your abdomen and thigh-buttocks area and muscle cells from underneath the skin of your leg. First, the doctor cleans and anesthetizes a small area of skin. Then a small incision is made in the skin and a needle is introduced under the skin to remove the fat or muscle cells. About 1 gram (less than half a teaspoon) of fat and about 150 milligrams (less than one eighth of a teaspoon) of muscle will be removed. After the biopsy is completed, the skin will be held closed with a sterile adhesive bandage and an antibiotic ointment will be applied.

Psychological tests: You will be given several forms to complete. You will also be asked to complete short tasks (provide word definitions, repeat aloud numbers and object/animal names that are read to you). You will also need to answer background information questions (i.e. age, occupation, highest education level achieved, etc.) and other questions pertaining to your cognitive and emotional state.

Core temperature: This test measures your body temperature over 24 hours. In the evening you will swallow a temperature capsule. This capsule will constantly send a radio signal to a recorder worn on your belt to record your temperature.

DEXA: This test takes approximately 20 minutes. You will have to lie on a table in a hospital gown. The scanner uses low-dose X-rays to determine the amount of fat, bone and muscle in your body.

Doubly-labeled water: For this test you will provide a urine sample. After this we will ask you to drink a bottle of water that contains two atoms, which are called stable isotopes (non-radioactive). These atoms are normally found in water in very small amounts. The water you drink has been enriched with these atoms. During the rest of the day you will provide us with 2 more urine samples. You will then be asked to provide urine samples each week. This test will tell us how many calories you burn and about your level of physical activity.

Immune function testing: Immune status, an indicator of the body's ability to fight infection, will be assessed from measurements of delayed type hypersensitivity (DTH). DTH is an examination of the blood cells and response to vaccines. The DTH test is similar to an allergy or tuberculosis skin test.