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United States Department of Agriculture

Agricultural Research Service


Location: Human Nutrition Research Center on Aging

2013 Annual Report

1a.Objectives (from AD-416):
1. Develop and validate mathematical models for carbon kinetics that simulate energy intake, energy regulation, and their relationship to body composition and fat stores. 2. Develop and validate practical field tools for the assessment and management of sarcopenia, dehydration, zinc status and frailty in institutionalized and community living elderly.

1b.Approach (from AD-416):
Simple monitoring of isotope clearance in breath CO2 can provide quantitative information on average energy intake. Our approach includes the use of a single stable isotope administration (C-13 palmitic acid) and monitoring its disappearance in breath CO2. We will use both mathematical modeling and clinical validation of this approach. The development and validation of new portable body composition tools will include the comparison of a hand-held caliper X-ray absorptiometer against tissue analysis by computerized tomography and the full evaluation of a nondestructive method for rapid analysis of extracellular water by X ray fluorescence analysis for stable bromine. For free-living elderly, we expect that portable body composition tools will provide an additional way to help monitor their medical, functional, and nutritional status so that they can extend safely their independent living.

3.Progress Report:

The main goal of this research is to validate a new method for measuring energy intake based on the rate of C-13 isotope disappearance in breath. Results from an initial experiment were used to determine the dose of C-13 labeled food, distribution of isotope in compartments as well as the optimum experimental procedures for collecting and analyzing breath samples. Based on the findings of our first experiment, we designed and completed a second study with 14 volunteers. The study was performed in our institution’s metabolic research unit (MRU), where the subjects received all their meals. A single dose of a fatty acid (palmitic acid fully labeled with C-13) was given with food on day one. Food and activity records were kept. Body composition, energy expenditure and C-13 breath samples were collected throughout the duration of the study. A mass spectrometer was used for analysis of the breath samples in order to establish the long term clearance curves for the given C-13 dose and to determine the parameters contributing to the rate of disappearance and to the long-term signal-to-noise ratio. A mathematical model was also used to interpret the long-term isotope kinetics. Initial analysis shows a linear correlation between energy intake and the rate of isotope disappearance, a necessary condition for the validity of the method. A field validation study was designed based on the results. We continued the development and validation of a hand-held caliper that uses x-ray absorptiometry to measure the composition of soft tissue. A series of mid-thigh 512x512 CT (computerized tomography) images from a clinical study were used to validate the performance of the instrument. A computer simulation was developed to compare the analysis of the images by CT against soft tissue composition measurements by the instrument. The analytical performance of the instrument was validated. In addition, this comparison against CT resulted in some design modifications to increase the amount of tissue evaluated by the instrument for the same amount of radiation exposure. All findings will be considered for the final instrument design. Based on this work, researchers concluded that a hand-held X-ray absorption instrument can be a safe and practical tool for body composition monitoring of the elderly in the field, in nursing homes or at bedside. Adding some imaging capabilities to the data processing will facilitate the instrument’s use in the field by eliminating re-positioning errors. We used a number of biological samples to test the portable x-ray fluorescence (XRF) analytical instrument, which was developed in our laboratory. We specifically tested its ability to analyze bromine in plasma, serum, saliva and urine. In some cases, the biological samples were spiked with a known amount of NaBr in order to demonstrate the linearity and range of the instrument’s response. The method was optimized for isotope dilution studies requiring extracellular water (ECW) for body composition measurements by Br dilution. The investigators completed the testing of this new instrument and concluded that its performance fully meets the requirements of ECW measurements with Br analysis. The device performed slightly better in plasma than in serum because of better sample uniformity. Its reproducibility was close to 1%. It was also demonstrated that this type of analysis is completely non-destructive and preserves 100% of the specimen without inducing any physical or biochemical alterations to it.

1. Composition Monitoring in the Field. NaBr dilution is an established method for measuring extracellular water, the fluid that is not contained in cells. Expansion of this water compartment indicates loss of muscle, frailty or acute disease. The current established analytical method is complicated, expensive and requires extensive sample preparation. ARS-funded researchers at JMUSDA-HNRCA at Tufts University, at Boston, Massachusetts developed a new, simple and safe method for rapid analysis of bromide in any body fluid, including blood plasma, serum, urine, or saliva which requires that the subject drinks a small amount of NaBr solution followed (3 hours later) by the collection and analysis of a blood or urine specimen for the presence and amount of bromide. A small specimen is analyzed in its original plastic vial by X-ray irradiation emitted by a microscopic radioactive source using X-ray fluorescence (XRF) and modern photon detection techniques. The device is inexpensive, portable, requires minimal power and is capable of high precision measurements (1%). None of the liquid specimen is consumed or altered during this analysis which allows the vial that contains the sample to remain sealed for the whole process. With the advent of this methodology, it is possible to easily monitor nutrition status of the elderly and help identify nutritional and health deficiencies before they develop into serious conditions.

Last Modified: 7/31/2014
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