Emerging Technologies for Nutrition Research Potential for Assessing Military Performance Capability (1997) / Chapter Skim
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Emerging Technologies for Nutrition Research, 1997 Pp.
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and I/B in many different subject populations by several laboratories, with a demonstrated precision (coefficient of variation) of 2 to 8 percent (Schoeller, 1988)
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has since been validated in soldiers under various conditions (DeLany et al., 1989; Forbes-Ewan et al., 1989; Hoyt et al., 1991, 1994)
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on the turnover of the two isotopes, which is dependent on H2O and CO2 output. For studies in typical adults, the optimal metabolic period is 4 to 21 days (Schoeller, 1988)
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multipoint DLW protocol, samples are obtained throughout the period, and elimination rates are calculated by regression analyses. The rationale of the multiple-point method is that by using more time points to calculate elimination rates, sample-to-sample variation (analytical error)
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energy expenditure and water turnover towards the end of the metabolic period due to environmental extremes (DeLany et al., 1991)
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between the two isotope dilution spaces. The ratio between the 2H and 18O dilution spaces (ND/NO)
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PARTICULAR CONCERNS FOR MILITARY NUTRITION DLW STUDIES Additional concerns when applying the DLW method to military nutrition studies are changes in baseline isotope during the study, the possible need for a higher dose of isotope and the need for administration of multiple doses of DLW to obtain energy expenditure during a long training study. For typical DLW studies, the baseline isotope abundance is measured before administration of the DLW and is assumed to remain constant throughout the study.
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Figure 12-4 Washout of isotope due to high water turnover. 0/00, ratio per mille derivations in heavy isotope ratio relative to standard mean ocean water (smow)
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Drawbacks of the DLW Method The major drawbacks of the DLW method are cost of the 18O-labeled water and the cost and technical difficulties associated with the isotope analyses. The need for an expensive isotope ratio mass spectrometer and sample preparation systems limits the number of laboratories that can carry out the method on-site.
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• Careful planning is required so that the optimum dosing and specimen collection protocol are utilized based on (1) estimated water turnover and energy expenditure, and (2)
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James, W.P.T., J.P. Haggarty, and B.A.
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Schoeller, D.A., R.F. Kushner, and P.J.H.
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riod of the water. Or depending on what point you have, if you are taking only two of them, you can change the slope of that line, depending on where you are.
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ROBERT WOLFE: Since you made the case so strongly for the two-point method, the other thing I would add that there is a potential advantage to collecting multiple points. It is that you use the jackknife technique to examine bad data points.
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JAMES DeLANY: It does not appear to be as good as energy expenditure, but some of the data that Tanya Jones has been compiling, some of the data that we have collected regarding the use of isotope versus the canteen measurements, look really good, with a correlation of maybe 0.85 between the measured intake and the isotope measurement of water turnover. JOAN CONWAY: Do you need doubly labeled water to do the water flux?
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