Metabolic Assessment Core
The Metabolic Core at the Rockefeller University Center for Clinical and Translational Science offers investigators the use of several metabolic and body composition testing devices that they can incorporate into their protocols. Below is a brief description of each test. For more information, please contact the Bionutrition Department at 212-327-8397.
Estimation of Resting Energy Expenditure
The VMAX Encore Indirect Calorimeter is used to determine resting metabolic rate. This test is important to those investigators who are conducting metabolic diet studies and who need to accurately assess a subject's weight maintenance calorie needs. Respiratory Quotient (RQ) measurement is also available to determine what substrate a subject is burning for fuel at a given time-point.
Free Living Energy Expenditure
To measure free living energy expenditure, the "Intelligent Device for Energy Expenditure and Activity" (IDEEA; MiniSun, Fresno, CA) can analyze body motion, measure physical activity, monitor behavior patterns, and estimate energy expenditure in a free-living situation on 24-hour basis. The IDEEA consists of five small sensors that are attached to the body via flexible cables: one on the chest, two on the anterior part of thighs, and two on the feet. The IDEEA is a small 200-gram data collection device that can be clipped to a belt. During testing periods, subjects are connected to the device for 3 days while they perform ad lib activities. The output analyses include assessment of physical activity and energy expenditure, with high accuracy of activity type identification.
The VMAX Encore is capable of performing exercise testing when combined with a treadmill or ergonomic cycle. VO2 Max, heart rate and blood pressure are measured as a subject performs a timed, incremental exercise test to determine baseline exercise capabilities, or improvement/detraining over time.
Body Composition Measurements
The BodPod Body Composition Tracking System provides accurate, fast and safe measurements of body fat and lean body mass using air displacement technology. By measuring how much air a person's body displaces while enclosed in a known volume container, the amount of body mass, fat and fat-free mass can be calculated. The BodPod offers a more convenient method of body composition analysis than hydrostatic (underwater) weighing, without sacrificing accuracy.
Total Body Water is a relatively low cost, highly accurate method of determining body fat mass. It can be determined through mass spectrometry using deuterium oxide (D2O) and Oxygen 18 stable isotope methods. The CCTS at Rockefeller University is now offering this test of body composition to its investigators. The principle is based on the theory that water is distributed in all parts of the body except body fat.
Total Body Dual energy X-ray absorptiometry (DEXA) scans measure fat and fat-free body mass. During a DEXA scan, the subjects will be positioned supine with their arms at their sides on the scanner. The software first divides pixels into bone mineral content and soft tissue compartments and then divides soft tissue compartments into fat-free mass and fat mass. Estimates of bone mineral content, total body fat mass, lean mass, and percent fat are generated, along with information about regional body fat distribution.
Regional Body Composition (subcutaneous fat, visceral fat, intramuscular fat, muscle and residual tissue) is assessed by magnetic resonance imaging (MRI) using a General Electric 3.0 Tesla Magnetic Resonance Imaging System with EXCITE hardware and software. The patient is positioned supine, and between 40-60 axial images with a thickness of 7-10 mm are acquired. The field of view (FOV) will be 36-48 cm, with a resolution of 256 x 256 pixels. Interpretation of the collected data will provide estimations of regional body composition.
MRI and DEXA measurements are body composition measurements available to investigators through our collaborators at Weill Cornell Medical Center.
Assessment of Physical Activity
Self-reported leisure time and occupational activity can be determined using the MONICA Optional Study of Physical Activity (MOSPA) questionnaire, which was developed for use in the World Health Organization's Monitoring Trends and Determinants of Cardiovascular Disease (WHO-MONICA) study. Subjects are shown how to properly use a pedometer, and are be asked to complete a log of the number of steps taken every day for 7 days during four periods (the baseline testing period, the weight stability period, the weight loss period, and the weight maintenance period). This log is submitted to study staff for analysis. The number of steps the person takes per day, and their average daily physical activity are used to determine the Activity Factor used in estimating Total Energy Expenditure for metabolic diet studies.
Insulin Sensitivity Measurement
To measure insulin sensitivity, a hyperinsulinemic euglycemic clamp is used. Briefly, two intravenous catheters are placed in the subject's arms. One catheter (placed in a deep antecubital or brachial vein) is used for infusion of insulin and dextrose, and one catheter (placed in a hand or wrist vein) is used for sampling of arterialized blood. Arterialization of venous blood is achieved by placing the hand in a hand warmer. Insulin is infused at a rate of 80 mU per m2 of body surface area per minute, and 20% dextrose solution is infused to maintain the blood glucose level between 90 to 100 mg/dL. Blood glucose is monitored and recorded every five minutes throughout the procedure, and blood insulin levels are checked five times during the procedure. Once a steady-state has been reached (i.e. euglycemia is maintained with a constant rate of dextrose infusion), the insulin-mediated glucose utilization rate (M, in mg/kg/min) can be calculated. This calculation provides an estimate of peripheral insulin-mediated glucose utilization, or insulin sensitivity.
Adipose Tissue Aspiration Biopsy for fatty acid analysis, gene expression profiling, and adipose tissue inflammation
A small sample of fat tissue is removed from a subject for genechip analysis. This procedure involves sterilizing the skin with alcohol and iodine-containing soap, then temporary numbing an area of skin on the abdomen or gluteal muscle with an injection of lidocaine, followed by needle aspiration of approximately 3 grams of adipose tissue from just beneath the skin. RNA is extracted from the adipose tissue biopsy and is applied to genechip arrays to study genes that are differentially expressed in fat tissue.