Body Composition Methodologies
During a body composition visit, many methodologies are employed to obtain data on various functions and characteristics comprising the "body composition" of our participants. Below is a brief description of the types of samples taken and outcomes observed in the numerous methodologies involved during such a body composition visit. All methodologies are performed on a pre-determined schedule for those Fels Longitudinal Study participants consenting to participate in that portion of the testing. For a more detailed description of any of the methodologies described below, follow the appropriate link.
Anthropometry, the measurement of body parts, is completed on all participants at a variety of ages and growth ranges. Circumferences, bone breadths, lengths, weights and skinfolds are measured and recorded for various regions on each individual. Techniques in anthropometry and anthropometry for the elderly have been an area of interest for the Lifespan Health Research Center's staff.
Dual energy x-ray absorptiometry (DXA) is performed on participants who fit the height and weight parameters of the Lunar densitometer. By scanning different anatomical regions, total body as well as segmented determinations may be made for, among other variables, bone mineral content, bone mineral density, muscle mass and percent of body fat.
Leanness, or specifically the amount of fat free mass, as well as total body fat and percent body fat is measured through the use of underwater weighing. In order to precisely calculate the amount of fat free mass, the lung residual volume is calculated to determine the volume of trapped air at maximal expiration. The amount of trapped air in the lungs adds more "float" to the individual, simulating increased body fat.
Bioelectrical impedance testing is performed in order to determine the amount of various body fluids as well as a measure for leanness. Electrodes are placed upon hands and feet and a small electrical current is passed through the body.
Measurements for subcutaneous fat is made through the use of ultrasound. Ultrasound is performed and measured on participants at 5 key sites on the body. Subcutaneous fat is also measured through the anthropometry portion of the testing.
Total body water is determined by the method of deuterium oxide (D2O) dilution. Deuterium is a non-radioactive naturally occurring molecule of water. The hydrogen atoms in deuterium are heavier than those that normally combine with oxygen to form water. Saliva samples are collected before other testing begins to establish a baseline measure of deuterium in the saliva. An amount of pure D2O is weighed, measured, and added to de-ionized water which is given to participants to drink. After a two hour fast and no urine eliminations, another saliva sample is taken and the amount of D2O remaining in the saliva is measured.
Fasting blood samples are collected on participants by a venous draw. From these samples levels of glucose, total cholesterol, triglycerides, high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), and the apolipoproteins A1, A2, and B are observed. Samples are also taken to determine the levels of the hormones DHEA SO4, estradiol, free testosterone, total testosterone, and insulin within participants between the ages of 8 and 18 and in females over 40. Since estradiol levels fluctuate during the menstrual cycle, we attempt to collect estradiol samples on day 21 ± 3 of the menstrual cycle in those not taking oral contraceptives and on day 14 ± 3 of the cycle of those taking oral contraceptives.
Hand radiographs of the participants from age 8 through 18 are also taken. These radiographs are assessed to determine the skeletal ages of the individual and are scored through various established skeletal maturation assessment procedures.
Other data is also gathered through the use of questionnaires. Surveys are filled out by the participants to find out medical history, physical activity, tobacco and alcohol use, sexual maturity, and for females, menstrual history. For each visit, the participant fills out the relevant forms, updating us on this information.