Measuring and evaluating growth and body composition is a very important component of our research studies. Our Body Composition Laboratory is equipped with the best available techniques and equipment to measure growth and body composition in our participants. We can accurately and precisely measure body fat, bone mineralization and body water. Questions such as whether specific infant diets promote better growth and development, or whether nutrition during pregnancy can be predictive of an infant’s susceptibility to diseases later in life can only be answered with research using precise body composition measurements.
The Body Composition Laboratory develops and validates new methods for assessing body composition in children. One great example is our newly acquired quantitative nuclear magnetic resonance (QMR) device. Data from the Body Composition Laboratory research is also being used to develop age and gender specific body composition standard references such as body composition in newborns and infants up to 6 months of age.
The Body Composition Laboratory also uses air displacement plethysmography (BodPod and PeaPod) to measure whole body fat, lean and water mass. Additional methods include stable isotope dilution for measuring the body’s water compartments and dual-energy x-ray absorptiometry (Hologic QDR 4500) for measuring bone, fat and lean-body mass. Peripheral quantitative computerized tomography (pQCT) is used to assess bone quality in older children.
Quantitative Nuclear Magnetic Resonance (NMR)
The quantitative nuclear magnetic resonance technology creates contrast between soft tissues by taking advantage of the differences in relaxation times of the hydrogen nuclei spins in these tissues, leading to a precise and accurate measure of body fat, fat free mass and total water. NMR has been successfully utilized in small animals of different sizes (mice, rats, marmoset) and in human adults. The Body Composition Laboratory uses the EchoMRI-AH for infants and children up to 50 kg (Echo Medical Systems). This device has been custom designed to accommodate our pediatric population. The two major advantages of this technology are: 1) the children do not need to be still in order to obtain high quality data; and 2) the same instrument can be used to study a given child from birth through puberty (or 50 kg). Children are positioned lying on their back and slid into the instrument for less than 3 minutes.
Air Displacement Plethysmography (ADP)
The air displacement plethysmography technology provides a precise and accurate measure of fat mass. The Body Composition Laboratory uses the BodPod for children and adults and the PeaPod for infants up to 6 months old (Life Measurement, Inc.). This technique measures body weight and body volume. The body density obtained from these measures helps in estimating body fat and lean mass. The participant enters the closed chamber where pressure is monitored to calculate the body volume.
Dual Energy X-ray Absorptiometry (DXA)
The DXA technology provides a very precise and accurate measure of bone mass. It can also measure fat and lean body mass. The Body Composition Laboratory uses the Hologic QDR 4500 with a discovery upgrade (Hologic). This technology uses high and low levels of X-ray to detect differences between bone and soft tissues. Participants need to remain still during the scanning process. The radiation exposure using DXA scanning is very low. In fact, it is lower than the exposure obtained during an airplane flight from Denver to New York. Babies are first fed and allowed to fall asleep before being positioned face up on a platform for about 3 minutes while the instrument scans.
Stable Isotope Dilution
The dilution technique uses a non-radioactive isotope called deuterium (18O) to determine total body water, allowing the estimation of body fat and fat free mass. This technique has been shown to be accurate in predicting percent body fat mass. The dilution technique is used as a criterion method in our validation studies. In combination with DXA and ADP, the dilution technique provides us a three-compartment model accurately and precisely assessing body composition. The dilution technique requires at least two urine samples, one prior to the deuterium administration and one several hours following the deuterium administration.