Energy respiratory quotient

Another possible mechanism to explain the potential effect of dairy products on weight loss derives from the observation that intakes of dietary calcium and dairy products have been associated with increases in energy expenditure and a lowered respiratory quotient. A lower respiratory... 

Insulin is probably the most important inhibitor of lipolysis. In contrast to adults, in whom catecholamines represent the most important stimulators of lipolysis, thyrotropin (TSH) is the most important stimulator of lipolysis in the newborn. Plasma free fatty acid concentrations rise markedly in the first hours after birth in response to a marked increase in the TSH concentration and a fall in the insulin concentration. The fatty acids released from lipid stores are oxidized by some extrahepatic tissues (e.g., heart and skeletal muscle, kidney, intestine, and lung). Because the respiratory quotient (the ratio of carbon dioxide production to oxygen use) falls from a value of 1.0 (showing that carbohydrate oxidation is the primary source of energy) to a value of 0.8 to 0.9 (showing increasing oxidation of protein or fatty acids) at 2 to 12 hours of age, at a time when protein catabolism is usually insignificant, fatty acid oxidation must represent... 

Fuel Specific reaction enthalpy (kJ/g) Specific turnover Respiratory quotient = (C02)/ (02) Energy equivalency (kJ/mol 02)... 

Indirect calorimetry provides the ability to measure the relative contribution of macronutrients toward energy use. The measurements of expired carbon dioxide and consumed oxygen are used to calculate respiratory quotient (RQ). An RQ of 1.0 indicates use of carbohydrate solely, an RQ of 0.7 indicates use of fat solely, whereas an RQ of 0.85 indicates mixed use of macronutrients. Data in rats demonstrates a significant increase in using fat as an energy substrate following DAG oil infusion (gastric) as observed by a decreased respiratory quotient value between 3-5 hours post-infusion (15). 

One technique for assessing energy metabolism involves measurement of 05ty-gen consumption another involves measurement of arteriovenous (AV) differences. (A thiiid technique, measurement of the respiratory quotient, is discussed in detail in Chapter 5.)... 

The main goal of this chapter is to leam how to determine the body s overall style of energy metabolism, via respiratory quotient (RQ) measure-ntents, and to derive the daily energy requirement. A view of the stoichiometries of the glycolytic pathway, Krebs cycle, and pathways of fatty acid synthesis and oxidation will allow RQ calculations for each individual pathway. Glycolysis and the Krebs cycle were presented in Chapter 4, Fatt> add synthesis and oxidation are detailed here. The locations, at points along various metabolic pathways, whereCO2 is produced (in the Krebs cycle) and Oj is consumed (in the respiratory chain), are points of focus in this chapter... 

FIGURE 5,15 increase in respiratory quotients wi th inCiiCiise in energy content 0/ diet. (Redrawn with permits inn from Rlwyn i l al., ]979.)... 

FIGURE 5.15 Increase in respiratory quotients with increase in energy content of diet. (Redrawn with permission from Elwyn et ah, 1979.)... 

Respiratory Quotient Data from Human Studies Protein Oxidation and the Respiratory Quotient Calculating Energy Expenditures... 

Energy Yields, respiratory Quotients, and Reducing Equivalents (Reaction, Reaction 2, Reaction 3, Figure 12.9)... 

Indirect calorimetry, a technique that measures Oj consumption and COj production, can be used when more accurate determinations are required for hospitalized patients. A portable indirect calorimeter is used to measure oxygen consumption and the respiratory quotient (RQ), which is the ratio of Oj consumed to COj produced. The RQ is 1.00 for individuals oxidizing carbohydrates, 0.83 for protein, and 0.71 for fat. From these values, the daily energy expenditure (DEE) can be determined. 

Whole room calorimetry is considered the gold standard for measuring energy expenditure in humans. Although the subject is free to move around in the calorimetric chamber, spontaneous physical activity is greatly reduced. Furthermore, the measurement is carried out under strictly controlled, artificial environmental conditions and often is of short duration (<24 hr). However, indirect calorimetry does provide important information about the basal metabolic rate, respiratory quotient, sedentary energy expenditure, and sleeping metabolic rate. 

Black, A. E., Prentice, A. M., and Coward, W. A. (1986). Use of food quotients to predict respiratory quotients for the doubly-labelled water method of measuring energy expenditure. Hum. Nutr. Clin. Nutr. 40C, 381-391. 

Fig. 23.2 Energy expenditure and substrate oxidation. Data are presented as means SD. Indirect calorimetry was measured after a 10-h overnight fast. LCHAD-defident patients (n = 9 closed bars and closed circles) have a similar resting energy expenditure as control subjects (n = 9 white bars and open squares) expressed as mean kcal/day (a) or kcal/kg of fat-free mass (b). Resting respiratory quotient was significantly higher in the LCHAD-deficient patients (n = 9 gray box plot)...

The respiratory quotient (RQ), used in studies of energy metabolism and exercise physiology, is... 

Another goal of the USDA study was to determine whether CLA enhanced energy expenditure, lipolysis, or fat oxidation in humans, similar to the effects observed in animals. Accordingly, measurements of metabolic rate and respiratory quotient were made by indirect calorimetry, and stable isotope tracers of palmitate and glycerol were used to measure the rate of appearance of free fatty acids and glycerol as well as whole body lipolysis and apparent reesterification. CLA supplementation had no effect on metabolic rate or whole-body fat oxidation rate during rest or exercise. Similarly, CLA did not change lipolytic rate, fatty acid release from adipose tissue, or apparent FFA reesterification rates under conditions of rest or exercise (33). 

Animals do not normally obtain energy exclusively from either carbohydrate or fat. They oxidise a mixture of these (and protein). Consequently, in order to apply the appropriate thermal equivalent, it is necessary to know how much of the oxygen is used for oxidation of each nutrient. The proportions are calculated from what is known as the respiratory quotient (RQ).This is the ratio between the volume of carbon... 

This replacement in the mixture of carbohydrate by fat is accompanied by a decline in the non-protein respiratory quotient, and when the theoretical value for fat (0.7) is reached it can be assumed that energy is being obtained only from body reserves. In ruminants, an additional indication that the post-absorptive state has been reached is a decline in methane production (and therefore digestive activity) to a very low level. 

More direct evidence of utilization is the favorable effect fat emulsion administration has on body weight, the shift in respiratory quotient towards fat oxidation, and a rise in the concentration of blood ketones. Absolute evidence for the metabolism of the emulsified triglyceride is given by the conversion of C-labeled fat to C02 and C-phospholipids following its intravenous injection. Finally, the fact that when fat emulsions comprise an essential part of the energy source in complete parenteral nutrition, growth and development occur, shows in a very practical manner that such emulsions are indeed utilized (Hallberg et al , 1970 and Hakansson jet al., 1967). ... 

The respiratory quotient (RQ) is the volume of carbon dioxide produced divided by the volume of oxygen consumed in the tissues in a given period of time. The value of the RQ depends on the nature of the metabolic energy source. For carbohydrates, the RQ is 1, for fats it is 0.7 and for proteins it is 0.8, A healthy subject on an ordinary mixed diet of carbohydrate, fat and protein has an RQ of typically 0.85. The RQ is of significance in its influence on the difference in pH comparing arterial and venous blood, to be described next. 

Energy yield (kj/g) Oxygen consumed (L/g) Carbon dioxide produced (L/g) Respiratory quotient iCOJO ) Energy/ oxygen consumption (kJ/L oxygen)... 

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