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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An ideal tracer is chemically identical to the compound of interest (the tracee) but distinct in some characteristic that enables its precise detection.
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Only carbohydrate, fat, and protein oxidation contribute to the total CO2 production. Consequently, Rx, Ry, and Rz can be determined (see below)
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Solving for c, to express in terms of VO2: Therefore, From these equations, both the proportion of carbohydrate and fat oxidation (Equations 9-3 and 9-4) and the total rate of each in g/min (Equations 9-7 and 9-10)
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relative contributions of fat and carbohydrate are to be converted into absolute rates. Conventionally, this is accomplished by indirect calorimetry, but portable devices are available that can accomplish this in the field.
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TABLE 9-1 Substrate Oxidation Rates at Rest and During Exercise Carbohydrate Fat Subject Indirect Calorimetry Ratio Method Indirect Calorimetry Ratio Method Rest 1 1.81 1.58 1.50 1.58 2 0.59 1.00 1.80 1.65 3 0.00 0.26 2.25 2.12 4 0.27 0.65 1.86 1.72 5 2.27 2.38 1.48 1.44 6 0.93 0.80 1.72 1.77 Means ± SE 0.98 ± 0.36 1.11 ± 0.31 1.77 ± 0.12 1.71 ± 0.09 Exercise 1 60.48 59.41 2.92 3.37 2 36.83 29.89 5.78 8.62 3 33.98 32.99 8.38 8.80 4 37.00 38.02 9.74 9.34 5 22.49 30.44 11.25 8.03 6 45.71 59.38 5.77 3.22 Means ± SE 39.42 ± 5.20 41.69 ± 5.72 7.31 ± 1.25 6.90 ± 1.15 NOTE: Values are in mg·kg-1·min-1. SOURCE: Adapted from Romijn et al.
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resulting depletion of the bicarbonate pool invalidates indirect calorimetry as a tool to quantify substrate oxidation, yet this problem does not affect the validity of the breath ratio method because VO2 can still be determined accurately. The breath ratio method has an important advantage over traditional precursorproduct tracer methods to measure substrate oxidation, in that isotopic exchange is not a problem.
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about 1 hour. Data can be computed easily, as only algebraic equations are involved.
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(Romijn et al., 1993)
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This may occur because of an abundance of α -- glycerol phosphate, as occurs during hyperglycemia (Wolfe and Peters, 1987) , or because of a low rate of blood flow through the fat.
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The total rate of glycerol release is equal to the glycerol released from peripheral adipocytes plus the glycerol released from the intramuscular pool. Consequently, it is possible to calculate the rate of adipocyte (peripheral)
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Figure 9-2 Maximal contribution to energy expenditure derived from glucose and free fatty acids (FFA) taken up from blood and minimal contribution of muscle triglyceride and glycogen stores after 30 minutes of exercise, expressed as function of exercise intensity.
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used. This limits the experimental protocols so that the experimental procedure does not affect the endogenous kinetics of the substrate being traced.
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Wolfe, R.R., and E.J. Peters 1987 Lipolytic response to glucose infusion in human subjects.
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ROBERT WOLFE: I kind of skipped over some of the details. To the extent to which free fatty acids [FFA]
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ROBERT WOLFE: I presented values derived almost entirely in steady state conditions. The kinetic modeling in nonsteady state with a stable isotope is more complex, but I would say it can be done.
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