2011 Annual Report
After we established how fast a labeled fatty acid oxidizes in the body as fuel, we designed the second level of this experiment. We obtained institutional license and initiated the multiple-dose phase of the human study. Palmitic acid fully labeled with the stable isotope C-13 is given with food to volunteers after every dinner for two weeks. As predicted by our model, we observe elevated C-13 in breath carbon dioxide samples resulting from “burning” the labeled palmitic acid together with the other foods. The volunteers are receiving all their meals from the metabolic kitchen in our institution and provide us with several breath samples per day. At the mid-point of their participation, we change their caloric intake to a lower level. As a result we expect to observe even higher levels of C-13 in breath. Working backwards we can calculate the amount of “new carbon” entering the body as food, diluting the C-13 isotope. This experiment (in progress) is a response investigation to test the validity of our mathematical model and the first of its kind performed with human subjects. At its final form this work will produce a breath test method to calculate average energy intake in free-living adults. This year’s work also completed the evaluation of two instruments for rapid isotopic analysis in breath; a mass spectrometer and a laser absorption resonance cavity. We installed a dedicated mass spectrometer for this project. A computer code was developed in Visual Basic to test the effect of repeated measurements using the hand-held X-ray caliper instrument when measuring tissue composition at mid-thigh. Eleven computerized tomography (CT) images were used as input for the mathematical analysis. The computer program simulated soft tissue analysis for several variations of caliper re-positioning. We concluded that an error of 2mm in re-positioning translated into a % fat measurement error of 0-2%, depending on the specific morphology of the subject. Computer software for the X-ray Fluorescence (XRF) instrument for the analysis of bromine in plasma and urine was fully developed. It included the programming of the instrument’s microprocessor which controls the automation of the sample handling. We also fully developed the data acquisition software. The two programs work together for automated XRF analysis. A full prototype was tested. The instrument was designed for portability and use in the field.