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PubMed1997

On problems of calculating energy expenditure and substrate utilization from respiratory exchange data.

Indirect calorimetry based on respiratory exchange measurement has been successfully used from the beginning of the century to obtain an estimate of heat production (energy expenditure) in human subjects and animals. The errors inherent to this classical technique can stem from various sources: 1) model of calculation and assumptions, 2) calorimetric factors used, 3) technical factors and 4) human factors. The physiological and biochemical factors influencing the interpretation of calorimetric data include a change in the size of the bicarbonate and urea pools and the accumulation or loss (via breath, urine or sweat) of intermediary metabolites (gluconeogenesis, ketogenesis). More recently, respiratory gas exchange data have been used to estimate substrate utilization rates in various physiological and metabolic situations (fasting, post-prandial state, etc.). It should be recalled that indirect calorimetry provides an index of overall substrate disappearance rates. This is incorrectly assumed to be equivalent to substrate "oxidation" rates. Unfortunately, there is no adequate golden standard to validate whole body substrate "oxidation" rates, and this contrasts to the "validation" of heat production by indirect calorimetry, through use of direct calorimetry under strict thermal equilibrium conditions. Tracer techniques using stable (or radioactive) isotopes, represent an independent way of assessing substrate utilization rates. When carbohydrate metabolism is measured with both techniques, indirect calorimetry generally provides consistent glucose "oxidation" rates as compared to isotopic tracers, but only when certain metabolic processes (such as gluconeogenesis and lipogenesis) are minimal or / and when the respiratory quotients are not at the extreme of the physiological range. However, it is believed that the tracer techniques underestimate true glucose "oxidation" rates due to the failure to account for glycogenolysis in the tissue storing glucose, since this escapes the systemic circulation. A major advantage of isotopic techniques is that they are able to estimate (given certain assumptions) various metabolic processes (such as gluconeogenesis) in a noninvasive way. Furthermore when, in addition to the 3 macronutrients, a fourth substrate is administered (such as ethanol), isotopic quantification of substrate "oxidation" allows one to eliminate the inherent assumptions made by indirect calorimetry. In conclusion, isotopic tracers techniques and indirect calorimetry should be considered as complementary techniques, in particular since the tracer techniques require the measurement of carbon dioxide production obtained by indirect calorimetry. However, it should be kept in mind that the assessment of substrate oxidation by indirect calorimetry may involve large errors in particular over a short period of time. By indirect calorimetry, energy expenditure (heat production) is calculated with substantially less error than substrate oxidation rates.

Animals↗
PubMed2005

Calorimetric determination of amorphous content in lactose: a note on the preparation of calibration curves.

Calorimetric methods (isothermal or solution calorimetry) offer the ability to detect amorphous contents to 0.5% (w/w) or better in processed pharmaceuticals and calorimetric data are becoming more widely accepted in regulatory submissions. However, both methods require the construction of calibration curves, prepared using quantitative physical mixtures of entirely amorphous and entirely crystalline material. If the sample under investigation exists in two or more isomers or polymorphs, and the enthalpy of solution (solution calorimetry) or the enthalpy of crystallisation (isothermal calorimetry) are different for the isomers or polymorphs, then it must be ensured that the batch of material used to prepare the calibration samples has the same isomeric or polymorphic composition as the (processed) material to be tested. Here, we demonstrate the problems that may arise using lactose as a pharmaceutically important model substance. Calibration curves were prepared from solution calorimetry and isothermal gas perfusion calorimetry data using two batches of lactose (one predominantly anhydrous alpha-lactose and one predominantly beta-lactose). The calibration curves are shown to be significantly different for the two batches, and it is shown that quantification of the amorphous content of a processed sample of unknown isomeric composition is impossible, unless the calibration curve is prepared from the same batch of material as the processed sample. In addition, some of the other problems inherent in using isothermal gas perfusion calorimetry for amorphous content determination, such as wetting issues and the preparation of calibration standards that mimic processes samples, are discussed.

Calibration↗
PubMed1999

Calculated and measured oxygen consumption in mechanically ventilated surgical patients in the early post-operative period.

Oxygen consumption (VO2) measured by indirect calorimetry (Nellcor-Puritan-Bennett 7250; Carlsbad, CA, USA) has been compared with VO2 calculated by the Fick method in 22 volume-controlled ventilated general surgical patients in the early post-operative period. For 198 pairs of measurements, VO2 Fick and VO2 indirect calorimetry correlated significantly (y = 1.00x - 35.8, P = 0.0001, r = 0.77). VO2 indirect calorimetry was 212 +/- 32 mL min-1 and VO2 Fick was 177 +/- 41 mL min-1 (P = 0.0001). The bias was 35 +/- 26 mL min-1. This difference represents 16 +/- 13% of the total body VO2. VO2 calculated by the Fick method did not accurately predict VO2 measured by indirect calorimetry, and the two methods were not interchangeable. VO2 calculated by the Fick method underestimated VO2 as measured by indirect calorimetry by a systematic quantity that could be attributed, in part, to VO2 of the lung. Indirect calorimetry should be the preferred method for measuring total body VO2 in mechanically ventilated surgical patients.

Abdomen↗
PubMed2006

How accurate are predictive formulas calculating energy expenditure in adolescent patients with anorexia nervosa?

BACKGROUND & AIMS: To compare resting energy expenditure, measured by indirect calorimetry, to values estimated by different predictive formulas in adolescent patients with anorexia nervosa. METHODS: We studied 22 female in-patients with a mean age of 14.7 years (SD 1.2). Resting energy expenditure was measured by indirect calorimetry (Deltatrac II MBM-200). We compared measured resting energy expenditure to values estimated by several predictive formulas [Fleisch, Harris-Benedict, FAO, Schofield-HW, Schebendach] using the intraclass correlation coefficient and the Bland-Altman method. RESULTS: Body mass index increased significantly (P<0.001). Measured resting energy expenditure increased during hospitalization (P<0.05). All formulas overestimated resting energy expenditure with respect to indirect calorimetry except the Schebendach formula. The intraclass correlation between indirect calorimetry and the formulas were poor (0.09-0.20). We observed a poor clinical agreement (Bland-Altman). CONCLUSIONS: Body mass index and resting energy expenditure increased during hospitalization. The majority of the predictive formulas overestimate resting energy expenditure in adolescent patients with anorexia nervosa. Therefore, indirect calorimetry may be a very useful tool for calculating caloric requirements in these patients.

Adolescent↗
PubMed2006

Best practice methods to apply to measurement of resting metabolic rate in adults: a systematic review.

Several factors may alter apparent resting metabolic rate (RMR) during measurement with indirect calorimetry. Likewise, numerous indirect calorimetry measurement protocols have been developed over the years, and the methodology employed could influence test results. As part of a larger project to determine the role of indirect calorimetry in clinical practice, a systematic review of the literature was undertaken to determine the ideal subject condition and test methodology for obtaining reliable measurement of RMR with indirect calorimetry. Food, ethanol, caffeine, and nicotine affect RMR for a variable number of hours after consumption; therefore, intake of these items must be controlled before measurement. Activities of daily living increase metabolic rate, but a short rest (< or =20 minutes) before testing is sufficient for the effect to dissipate. Moderate or vigorous physical activity has a longer carryover effect and therefore must be controlled in the hours before a measurement of RMR is attempted. Limited data were found regarding ideal ambient conditions for RMR testing. Measurement duration of 10 minutes with the first 5 minutes deleted and the remaining 5 minutes having a coefficient of variation <10% gave accurate readings of RMR. Individuals preparing for RMR measurement via indirect calorimetry should refrain from eating, consuming ethanol and nicotine, smoking, and engaging in physical activity for varying times before measurement. The test site should be physically comfortable and the individual should have 10 to 20 minutes to rest before measurement commences. A 10-minute test duration with the first 5 minutes discarded and the remaining 5 minutes having a coefficient of variation of <10% will give an accurate measure of RMR.

Adult↗
PubMed1994

A calorimetric study of the thermal stability of barnase and its interaction with 3'GMP.

We have used high-sensitivity differential scanning calorimetry to characterize the thermal stability of barnase from Bacillus amyloliquefaciens in the pH range 2.0-5.0. The energetics of the interaction between barnase and its inhibitor 3'GMP have been studied by isothermal titration calorimetry in the temperature range 15-30 degrees C. Scanning calorimetry experiments were also made with the protein in the presence of various concentrations of 3'GMP at pH 4.5. A novel, simple procedure is proposed to obtain binding parameters from scanning calorimetry data. This method is based on the calculation of the partition functions of the free and the ligand-bound protein. Isothermal calorimetry shows that at 25 degrees C 3'GMP binds to a single site in barnase with a delta Cp of -250 +/- 50 J/(K.mol). Both free barnase and ligand-bound barnase undergo a highly reversible, two-state thermal unfolding process under our experimental conditions. delta G and delta Cp unfolding values are similar to others found for globular proteins, whereas delta H and delta S unfolding values are unusually high at the denaturation temperature of barnase. We have also found unexpectedly that the thermodynamic unfolding parameters of barnase fit neither the trend of values described in the literature for the correlation between delta Cp and delta H nor the limiting specific enthalpy value in the correlation between delta H and Tm for globular proteins. These discrepancies might be related to particular features of the folded and/or unfolded states of the protein.

Bacterial Proteins↗
PubMed1994

Clinical comparison of three methods to determine resting energy expenditure.

An accurate and reliable method of determining resting energy expenditure in the critical care setting is crucial because inadequate caloric intake and excessive caloric intake are both associated with a number of complications. Energy requirements were determined by three different methods in a group of 25 post-cardiac surgery patients in the intensive care unit. Patients were intubated and had a thermodilution pulmonary artery catheter in place. The first method measured resting energy expenditure by indirect calorimetry. For the second method, the results of blood gases drawn at the same time that indirect calorimetry was measured were used in the Fick equation. In the third method, a registered dietitian assessed each patient by using the Harris-Benedict equation with stress factor modification. Indirect calorimetry was considered the standard with which the other two methods were compared. The results showed that, compared with calorimetry, both the Fick equation and the Harris-Benedict equation underestimated resting energy needs. Statistically, only the difference between the Fick equation method and indirect calorimetry was significant. Clinically, however, both methods seem to have applicability.

Adult↗
PubMed2004

Retrospective evaluation of commonly used equations to predict energy expenditure in mechanically ventilated, critically ill patients.

STUDY OBJECTIVE: To determine which of four commonly used equations to estimate energy expenditure is precise and unbiased compared with energy expenditure as measured by indirect calorimetry. DESIGN: Retrospective, observational study. SETTING: Adult medical intensive care unit in a research hospital of the National Institutes of Health Clinical Center. PATIENTS: Seventy-six adult, mechanically ventilated, critically ill patients. INTERVENTION: Indirect calorimetry reports generated by the National Institutes of Health Critical Care Medicine Department's Metabolic Cart Consult Service were reviewed. Bias and precision of resting energy expenditure (REE) estimated by equations were computed using mean prediction error (ME) and root mean squared prediction error (MSE). Equations were considered precise if the 95% confidence interval for MSE was within 15% of the measured energy expenditure (MEE) determined by indirect calorimetry. Equations were considered unbiased if the 95% confidence interval for ME included zero. Paired t tests were used to compare estimated REE values for each predictive equation with MEE values determined by indirect calorimetry. Data were stratified into regions of bias using classification and regression tree analysis, as well as visual inspection of estimated REE-versus-MEE curves for each equation. MEASUREMENTS AND MAIN RESULTS: The Harris-Benedict equation multiplied by an activity factor of 1.2 was unbiased and precise. The Ireton-Jones equation was precise but biased. The American College of Chest Physicians' consensus recommendation was biased and imprecise. The Harris-Benedict equation without an activity factor also demonstrated bias and imprecision. CONCLUSIONS: The Harris-Benedict equation multiplied by an activity factor of 1.2 is suitable for predicting REE and may be used in the absence of indirect calorimetry.

Adult↗
PubMed2002

Energy requirements in critically ill patients: how close are our estimates?

A retrospective analysis of 55 mechanically ventilated critically ill patients was conducted to determine adequacy of nutritional support (total parenteral nutrition or enteral nutrition) according to requirements established by indirect calorimetry. Patients who received 90% to 110% of the established energy requirements as measured by indirect calorimetry were defined as adequately fed. At the time of the indirect calorimetry measurements, all patients were receiving their targeted nutritional support, as assessed by the unit dietitian, who used predictive formulas to assess patients. Indirect calorimetry results showed that 25% of the patients were overfed (receiving >110% of energy requirements), 35% were underfed (receiving <90% of energy requirements), and 40% were adequately fed (receiving 90% to 110% of energy requirements). We determined that critically ill patients with a body mass index <20 kg/m2 were the most likely group to be assessed inappropriately by available regression equations. If indirect calorimetry measurement is unavailable, we suggest using an empiric formula of 37 kcal/kg for critically ill patients with a body mass index <20 kg/m2.

Journal Article↗
PubMed1986

Calculation versus measurement of total energy expenditure.

In acutely ill patients both hypo- and hyperalimentation must be avoided by adjusting caloric intake to total energy expenditure (TEE). We determined the discrepancy between basal energy expenditure (BEE) calculated from the basic Harris-Benedict formula and TEE measured by continuous indirect calorimetry in a heterogeneous group of mechanically ventilated surgical patients. We also compared the accuracy of TEE calculated from the corrected Harris-Benedict formula or estimated by intermittent indirect calorimetry to that of TEE measured by continuous indirect calorimetry. The poor correlation between calculated BEE and measured TEE was significantly (p less than .05) improved by a correction factor based on each patient's clinical condition. The mean absolute difference between calculated TEE and measured TEE was 8.9 +/- 9.6 (SD) %. Calculations were significantly (p less than .05) improved by estimating TEE from two 5-min recording periods, which suggests that continuous indirect calorimetry may not always be necessary to guide caloric replacement.

Adolescent↗
PubMed1996

Residual analysis in the determination of factors affecting the estimates of body heat storage in clothed subjects.

Body heat storage can be estimated by calorimetry (from heat gains and losses) or by thermometry [from changes (delta) in mean body temperature (T b) calculated as a weighted combination of rectal (Tre) and mean skin temperatures (T sk)]. If an invariant weighting factor of Tre and T sk were to be used (for instance, delta T b = 0.8.delta Tre + 0.2 delta T sk under hot conditions), body heat storage could be over- or underestimated substantially relative to calorimetry, depending on whether the subject was wearing light or protective clothing. This study investigated whether discrepancies between calorimetry and thermometry arise from methodological errors in the calorimetric estimate of heat storage, from inappropriate weightings in the thermometric estimate, or from both. Residuals of calorimetry versus thermometric estimates were plotted against individual variables in the standard heat balance equation, applying various weighting factors to Tre and T sk. Whether light or protective clothing was worn, the calorimetric approach generally gave appropriate estimates of heat exchange components and thus heat storage. One exception was in estimating latent heat loss from sweat evaporation. If sweat evaporation exceeded 650 g.h-1 when wearing normal clothing, evaporative heat loss was overestimated and thus body heat storage was underestimated. Nevertheless, if data beyond this ceiling were excluded from the analyses, the standard 4:1 weighting matched calorimetric heat storage estimates quite well. When wearing protective clothing, the same 4:1 weighting approximated calorimetric heat storage with errors of less than approximately 10%, but only if environmental conditions allowed a subject to exercise for more than 90 min. The best thermometric estimates of heat storage were provided by using two sets of relative weightings, based upon the individual's metabolic heat production (M in kilojoules per meter squared per hour): (4 - [(M - x).x-1].2): 1 for an initial, thermoneutral environment and (4 + [(M - x).x-1].5):1 for a final, hot environment, the optimal value of x lay between 450 and 500 kJ.m-2.h-1. We concluded that the accuracy of thermometric estimates of heat storage can be improved by modifying weighting factors of Tre and T sk according to the environment, type of clothing, and metabolic rate.

Adult↗
PubMed2005

The agreement between the MedGem indirect calorimeter and a standard indirect calorimeter in anorexia nervosa.

OBJECTIVES: Measurement of the basal metabolic rate (BMR) can be used to estimate the calories required for weight gain during refeeding in anorexia nervosa (AN). The reference method for measuring the BMR is indirect calorimetry. MedGem has developed a new indirect calorimeter that calculates the metabolic rate much more quickly than standard indirect calorimeters. This study compared the BMR measured by the MedGem and standard indirect calorimetry in an AN population. METHODS: We measured the BMR using the Deltatrac metabolic cart followed immediately by the MedGem indirect calorimeter in 27 subjects (12 patients and 15 controls). RESULTS: Bland-Altman plots show that there is poor agreement between the BMR reported by the MedGem compared to the Deltatrac. DISCUSSION: Until better agreement with standard indirect calorimetry can be shown the MedGem should not be used for calorimetry in AN. Possible factors that may limit the MedGem's reliability include patient discomfort with the mouthpiece, use of a fixed RQ, and the short sampling period.

Adult↗
PubMed1991

Ascites increases the resting energy expenditure in liver cirrhosis.

The purpose of this study was to investigate the effect of ascites on the energy metabolism of patients with liver cirrhosis. The resting energy expenditure was determined in 10 patients with liver cirrhosis and ascites of moderate or large volume. The resting energy expenditure measurement was performed using indirect calorimetry and the resting energy expenditure predictive value was calculated with the Harris-Benedict equation, both before and after removal of ascitic fluid by paracentesis. Metabolic stress factors were absent in all cases. After an interval of 11.2 +/- 7.7 days between measurements, a weight loss of 16.6 +/- 10.3 kg was observed with paracentesis. The resting energy expenditure measured by indirect calorimetry showed a statistically significant decrease from 1682 +/- 291 to 1523 +/- 240 kcal/day (P less than 0.005) after removal of ascites. The repeatability of our indirect calorimetry method only allowed for the analysis of the results in 4 of 10 patients in whom ascites removal produced a consistent decrease in resting energy expenditure. There were no statistically significant differences between the measurements obtained by indirect calorimetry and those provided by the Harris-Benedict equation, but the latter had a moderate reliability in predicting the real resting energy expenditure of every patient. Our results suggest that, far from being an inert volume, ascites may be associated, at least in some patients, with an increased resting energy expenditure and therefore accelerate the appearance of protein energy malnutrition with corresponding complications.

Adult↗
PubMed2004

Sorbitol prevents the self-aggregation of unfolded lysozyme leading to and up to 13 degrees C stabilisation of the folded form.

We present a calorimetric investigation of stabilisation of hen egg-white lysozyme with sorbitol in the pH range 3.8-10.5. Differential scanning calorimetry and steady-state fluorescence were used to determine the denaturation temperatures of lysozyme as a function of sorbitol concentration. The fluorescence data were collected in the presence of 2M urea to lower the melting point of the protein to an observable range of the instrument. The effect of sorbitol on the activation energy of unfolding was investigated by scanrate studies. The effect of sorbitol lysozyme interaction was investigated using isothermal titration calorimetry. The titration experiments were performed with folded as well as unfolded lysozyme to investigate in more detail the nature of the interaction. The data obtained in those experiments show a remarkable stabilisation effect of sorbitol. We observed a 4.0 degrees C increase in the Tm for 1 M sorbitol in the pH range 3.8-8.5 by scanning calorimetry. The effect increases dramatically at pH 9.5 where we observe a 9.5 degrees C stabilisation. An increase in the sorbitol concentration to 2 M stabilises lysozyme by 11.3-13.4 degrees C in the pH range 9.5-10.5. In the absence of urea, no significant effects of sorbitol were observed on the activation energy for unfolding for lysozyme at pH 4.5. This indicates together with the results from the titration experiments that sorbitol may stabilise the folded form of lysozyme by destabilising the unfolded form of lysozyme. At pH values at and above lysozyme's pI (approximately 9.3), the unfolding of the protein is accompanied with a substantial amount of self-aggregation seen in the calorimetry experiments in the ratio of DeltaH(cal)/DeltaH(vH). In the presence of sorbitol, the self-aggregation was counterbalanced by higher sorbitol concentrations. These results strongly suggest a negative influence of sorbitol on the unfolded form of lysozyme and thereby stabilising the native form.

Calorimetry, Differential Scanning↗
PubMed1998

Solid-state characterization of chlordiazepoxide polymorphs.

A novel crystal form (form II) of the benzodiazepine chlordiazepoxide is reported. The new polymorphic phase was characterized and distinguished from the standard form (form I) by X-ray diffractometry, differential scanning calorimetry, infrared spectroscopy, microscopy, solution calorimetry, and solid-state nuclear magnetic resonance. The formation of form II was dependent on the crystallizing solvent, being the predominant form isolated from methanol. Recrystallization from other alcoholic solutions (ethanol, propanol, and butanol) and toluene yielded form I. Differential scanning calorimetry and powder X-ray diffraction indicated that the two forms were enantiotropically related with a transition of form II to form I occurring between 200 and 225 degreesC. Visual examination by hot stage microscopy in this temperature range revealed a dramatic solid-state transition. Single-crystal X-ray analysis was performed on form II which was found to crystallize in the triclinic space group P1 with a = 10.736(2) A, b = 16.921(4) A, c = 17.041(4) A, alpha = 100.76(1) degrees, beta = 95.27(1) degrees, gamma = 97.53(1) degrees, Z = 8, and dcal = 1.33 g/cm3. When compared with the published crystal structure of form I, the cell symmetry, volume, and density were similar. Both structures consisted of four crystallographically independent molecules linked in pairs through intermolecular hydrogen bonding. Differences were observed in the packing arrangement of the dimers in the polymorphs. The small heat of transition calculated from solution calorimetry (1.5 kJ mol-1) was sufficient to effect a crystallographic rearrangement of the dimers.

Calorimetry, Differential Scanning↗
PubMed2006

Comparison of resting energy expenditure in bronchopulmonary dysplasia to predicted equation.

OBJECTIVE: Children with bronchopulmonary dysplasia (BPD) often suffer from growth failure because of disturbances in energy balance with an increase of resting energy expenditure (REE). Evaluation of REE is a useful tool for nutritional management. Indirect calorimetry is an elective method for measuring REE, but it is time consuming and requires rigorous procedure. The objective of this study was to test accuracy of prediction equation to evaluate REE in BPD children. PATIENTS AND METHODS: Fifty-two children aged 4-10 years with BPD (30 boys and 22 girls) and 30 healthy lean children (20 boys and 10 girls) were enrolled. In this study, indirect calorimetry was compared to four prediction equations (Schoffield-W, Schoffield-HW, Harris-Benedict and Food and Agriculture Organization equation) using Bland-Altman pair wise comparison. RESULTS: The Harris-Benedict equation was the best equation to predict REE in children with BPD, and Schoffield-W was the best in healthy children. For the children with chronic lung disease of prematurity the Harris-Benedict equation showed the lowest mean predicted REE-REE measured by indirect calorimetry difference (difference = 15 kcal/day; limits of agreement -266 and 236 kcal/day; 95% confidence interval for the bias -207 to 177 kcal/day), and graphically, the best agreement. For the group of healthy children, it was the Schofield-W equation (-2.9 kcal/day; limits of agreement -275 and 269 kcal/day; 95% confidence interval for the bias -171 to 165 kcal/day), and graphically, the best agreement. CONCLUSION: Differences in prediction equation are minimal compared to calorimetry. Prediction equation could be useful in the management of children with BPD.

Basal Metabolism↗
PubMed2005

Calorimetric studies of melanotransferrin (p97) and its interaction with iron.

The mammalian molecule melanotransferrin (mTf), also called p97, is a member of the transferrin family of molecules. It exists in both secreted and glycosylphosphatidylinositol-anchored forms and is thought to play a role in angiogenesis and in transporting iron across the blood brain barrier. The binding affinity of iron to this molecule has not been formally established. Here, the binding of ferric ion (chelated with a 2-fold molar ratio of nitrilotriacetate) to mTf has been studied using isothermal titration calorimetry and differential scanning calorimetry. One iron-binding site was determined for mTf with similar binding characteristics to other transferrins. In the absence of bicarbonate, binding occurs quickly with an apparent association constant of 2.6 x 10(7) M(-1) at 25 degrees C. The presence of bicarbonate introduces kinetic effects that prevent direct determination of the apparent binding constant by isothermal titration calorimetry. Differential scanning calorimetry thermograms of mTf unfolding in the presence and absence of iron were therefore used to determine the apparent binding constant in the bicarbonate-containing system; at pH 7.5 and 25 degrees C, iron binding occurs in a 1:1 ratio with a K(app) of 4.4 x 10(17) M(-1). This affinity is intermediate between the high and low affinity lobes of transferrin and suggests that mTf is likely to play a significant role in iron transport where the high affinity lobe of transferrin is occupied or where transferrin is in proportionally low concentrations.

Animals↗
PubMed1991

The measurement of energy expenditure.

This is a brief account of the development of energy expenditure measurements, from speculations by early philosophers on the nature of the "innate fire," through the beginnings of quantitative animal calorimetry and to the combined material and energy balances of Rubner and of Atwater and Benedict, which established the science of nutritional energy. The equivalence of oxidation rate and heat loss led to the simplification of indirect calorimetry, followed by the era of studies of basal metabolic rate. Current practices are reviewed for measuring energy expenditure by indirect calorimetry (respiration chambers, ventilated hoods, doubly labeled water) and direct calorimetry (rooms, suits). Because problems remain in the exact account of energy balance during weight change, growth, pregnancy and exercise, perhaps it may be time to combine once again carbon balance with energy balance, using modern methods.

Calorimetry, Indirect↗