The basis of direct and indirect calorimetry and their potentials

Effects of Low Protein-High Carbohydrate Diet during Early and Late Pregnancy on Respiratory Quotient and Visceral Adiposity

Background

Low Protein-High Carbohydrate (LPHC) diet during pregnancy is considered a nutritional and health problem related to the development of maternal metabolic alterations, such as fatty liver and obesity in the perinatal and postnatal period. It is known that increase in visceral adiposity tissue (VAT) modulates maternal metabolic rate, with the respiratory quotient (RQ) being a parameter related to that variable; however, it is unknown whether LPHC intake during pregnancy affects the VAT and the RQ. In this study, we examine if consumption of LPHC during pregnancy modifies the VAT and RQ in early and late periods of pregnancy.

Methods

This is a longitudinal and cross-sectional study with Wistar rats during gestation (G) (3, 8, 15, and 20) and nonpregnant rats. Rats were fed with a control diet with 63/18% carbohydrate/protein and an experimental diet with 79/6% carbohydrate/protein. We studied water and food consumption and metabolic parameters such as RQ and energy expenditure (EE), calculated by indirect calorimetry. In the cross-sectional study, we determined visceral fat, as well as the concentration of free fatty acids, insulin, glucose, and lipid profile in serum.

Results

Nonpregnant rats with LPHC intake decreased significantly in VAT (86%) and the RQ (18%); in pregnant rats in early (8G) and late pregnancy (15G) in LPHC diet, both parameters (VAT and RQ) (25%-92%) increased during light time. When comparing time points during pregnancy in the control and LPHC groups, the RQ increased in 15G during daytime compared to 8G during the night period (17 and 5%, respectively). In late pregnancy, LPHC intake and triacylglyceride levels increased and cholesterol and glucose decreased (45 and 26%, respectively), in comparison to nonpregnant rats.

Conclusions

LPHC intake in nonpregnant rats decreases the RQ and VAT. Interestingly, the opposite occurs in early pregnancy: the RQ and VAT increased, and this correlates with free fatty acid (FFA) levels. The increase in RQ and VAT during light time in early pregnancy increased mobilization of carbohydrate and protein metabolism. These results suggest that LPHC intake during pregnancy increases the glucose metabolism as a compensatory mechanism for energy needs in the fetus and the mother in early pregnancy.

Effects of protein quantity and type on diet induced thermogenesis in overweight adults: A randomized controlled trial

BACKGROUND & AIMS

Protein content of a meal is hypothesized to drive DIT dose-dependently. However, no single meal study exists comparing two different doses of protein on DIT. In addition, the source of protein, particularly whey protein, was shown to have a higher DIT than casein and soy in the acute setting, however the mechanism behind this difference is not yet clear. The aim of the present work is therefore to evaluate the efficacy of two different doses and types of protein (whey protein and casein) on DIT in overweight adults.

METHODS

Randomized, double blind crossover including seventeen overweight men and women assigned to four isocaloric study treatments where protein and carbohydrate were exchanged: control, 30 g of whey protein microgels (WPM30), 50 g WPM (WPM50) or 50 g micellar casein (MC50). Energy expenditure was measured by indirect calorimetry. Blood, breath and urine samples were collected in order to measure substrate oxidation, amino acid profile, glucose and insulin, protein turnover and other metabolic parameters.

RESULTS

DIT was 6.7 ± 3.7%, 13.0 ± 5.0%, 18.0 ± 5.0% and 16.0 ± 5.0% for control, WPM30, WPM50 and MC50, respectively. There was a significant difference between WPM50 and WPM30 (p < 0.005) and a trend was observed between WPM50 and MC50 (p = 0.06). WPM50 resulted in the highest total, essential, and branched-chain plasma amino acid concentrations when compared with the other study treatments (p < 0.005) and a higher insulin concentration than MC50 (p < 0.005). Protein oxidation was higher for WPM50 than MC50. Protein turnover was significantly correlated with DIT through total leucine oxidation (r = 0.52, p = 0.005).

CONCLUSIONS

Our findings show that DIT does increase at a dose beyond 30 g of WPM and that the type of dairy protein may have an effect on DIT with WPM tending towards a higher DIT than casein. Although further research is required to understand the mechanism behind the effect of different protein sources on thermogenesis, we suggest that amongst the components of protein turnover, protein oxidation may be an important driver of thermogenesis at doses higher than 30 g. These results have concrete implications when choosing a dose of protein to optimize its thermogenic effect.

CLINICAL TRIAL REGISTRY NUMBER

NCT02303080 www.clinicaltrials.gov.

Evaluation of a short protocol for indirect calorimetry in females with eating disorders and healthy controls

BACKGROUND AND AIMS

To enable clinicians to identify the clinical picture and treatment progress and to adjust eating plans according to personal energy needs, it is important to know the patient's correct resting metabolic rate (RMR). Indirect calorimetry (IC) is the preferred method for assessment of RMR, but long duration of measurement increases the load on the patients, and reduces the effectiveness in clinical and scientific settings. Further; not all patients reach a valid RMR according to the suggested best practice protocol, with 5 min of steady state (SS) where respiratory gas volume exchange varies less than 10%. The aim of this study was to evaluate the possibility for an abbreviated RMR protocol and SS criterion.

METHODS

Forty two women diagnosed with bulimia nervosa or binge eating disorder (eating disorder group, ED), originally recruited for an outpatient treatment study, and 26 age and gender matched healthy controls (HC) were studied during a single, prolonged IC measurement. Participants rested for 10 min in supine position wearing a two-way breathing facemask, before a continuous measurement period of 20 min. Results from a standard 5 min SS criterion was compared to an abbreviated 3 min SS criterion. Both SS-criteria were evaluated through three different SS protocols (<10% variation in respiratory gas exchange), being: 1) measurement during the first 3 or 5 min, 2) measurement after discarding the first 5 min, and 3) the lowest identified RMR during the 20 min of measurement.

RESULTS

About 50% of the participants reached an early SS in both the defined SS minute criteria. Participants reaching a valid SS throughout the 20 min of measurement increased from ∼90% to 100% with an abbreviated 3 min SS. With a 5 min SS criterion, the median (range) RMR for the 3 protocols were 1639.9 (1239.2), 1508.8 (1457.6) and 1500.6 (1328.8) respectively for the ED group, and 1702.2 (1239.4), 1608.4 (1076.4) and 1594.8 (1029.2) respectively for the HC group, (p > 0.05 for all between-group analysis). With a 3 min SS criterion, the median (range) RMR were 1533.6 (1298.2), 1461.2 (1406.1), and 1395.8 (1447.3) respectively for the ED group and 1681.7 (1332.4), 1613.7 (1266.0) and 1523.1 (1050.3), respectively for the HC group, (p > 0.05 for all between-group analysis). Lowest measured RMR was different compared to the other two SS protocols in both the ED- and the HC group, and for both the 5 min- and the 3 min SS criteria, respectively (p < 0.04). Furthermore, a SS of 3 min resulted in lower RMR compared to 5 min SS (p < 0.00) and an increased number of participants classified as hypo-metabolic (RMRmeasured/RMRcalculated < 0.9).

CONCLUSIONS

An abbreviated measurement protocol to identify the lowest RMR using IC was not successful. Abbreviating the SS criteria from 5 to 3 min, resulted in a lower RMR, hence encouraging further examination of the validity of shorter SS criterion than practiced today. Registered in Clinical Trials by id-number NCT02079935, and approved by the Norwegian Regional Committee for Medical and Health Research Ethics with id-number 2013/1871. The trial in which control persons were recruited, is approved by the Norwegian Regional Committees for Medical and Health Research Ethics with the id-number 2016/1718, and prospectively registered in Clinical Trials with the id-number NCT03007459.

Effect of Body Position on Energy Expenditure of Preterm Infants as Determined by Simultaneous Direct and Indirect Calorimetry

Background Indirect calorimetry is the standard method for estimating energy expenditure in clinical research. Few studies have evaluated indirect calorimetry in infants by comparing it with simultaneous direct calorimetry. Our purpose was (1) to compare the energy expenditure of preterm infants determined by these two methods, direct calorimetry and indirect calorimetry; and (2) to examine the effect of body position, supine or prone, on energy expenditure. Study Design We measured energy expenditure by simultaneous direct (heat loss by gradient-layer calorimeter corrected for heat storage) and indirect calorimetry (whole-body oxygen consumption and carbon dioxide production) in 15 growing preterm infants during two consecutive interfeeding intervals, once in the supine position and once in the prone position. Results The mean energy expenditure for all measurements in both positions did not differ significantly by the method used: 2.82 (standard deviation [SD] 0.42) kcal/kg/h by direct calorimetry and 2.78 (SD 0.48) kcal/kg/h by indirect calorimetry. The energy expenditure was significantly lower, by 10%, in the prone than in the supine position, whether examined by direct calorimetry (2.67 vs. 2.97 kcal/kg/h, p < 0.001) or indirect calorimetry (2.64 vs. 2.92 kcal/kg/h, p = 0.017). Conclusion Direct calorimetry and indirect calorimetry gave similar estimates of energy expenditure. Energy expenditure was 10% lower in the prone position than in the supine position.

Prepregnancy body mass index influences lipid oxidation rate during pregnancy

INTRODUCTION

The influence of maternal body mass index (BMI) on respiratory quotient during pregnancy is not clear. We aim to evaluate longitudinal changes in energy expenditure, respiratory quotient, and substrate oxidation rates in normal and overweight women with uncomplicated pregnancies. We hypothesized that the threshold period in switching from a predominantly carbohydrate to a predominantly lipid metabolism may be different in normal and overweight women.

MATERIAL AND METHODS

Forty healthy pregnant women were recruited for a prospective cohort study. They were divided into two groups, normal and overweight (BMI <25 kg/m² or ≥25 kg/m² ). Comparisons of indirect calorimetry data were performed monthly throughout pregnancy. The relationships between energy and substrate metabolism variables and maternal BMI were also analyzed.

RESULTS

There was a significant increase in oxygen consumption (Vo₂ ), carbon dioxide production (Vco₂ ) and resting energy expenditure during pregnancy in both normal and overweight women. In the normal weight group, respiratory quotient decreased during the second trimester and increased in the last trimester. Respiratory quotient was lower in the overweight group in the second trimester and decreased in the last trimester; between-group differences being significant at 20 and 36 weeks (0.85 ± 0.06 vs. 0.81 ± 0.01, p = 0.009; 0.87 ± 0.05 vs. 0.80 ± 0.03, p = 0.01, respectively). Lipid oxidation was significantly higher in overweight women at both 20 and 36 weeks (36.8 ± 19.7% vs. 55.2 ± 5.6%, p = 0.003 and 33.6 ± 18.2% vs. 59.6 ± 12.7%, p = 0.007, for normal and overweight group, respectively).

CONCLUSION

Prepregnancy maternal BMI influences lipid oxidation rate and respiratory quotient during pregnancy.

Characterizing Energy Expenditure During Sedentary Behavior After Stroke

OBJECTIVES

To measure and calculate the energy expended by people with stroke during near sedentary behaviors (lying, supported and unsupported sitting, standing, wheelchair propulsion, walking), under controlled laboratory conditions, and to compare these values with the energy expenditure of 1.5 metabolic equivalent task (MET) within the definition of sedentary behavior.

DESIGN

Cross-sectional cohort study.

SETTING

Rehabilitation institutions.

PARTICIPANTS

People with stroke (N=27; mean age, 61.0±11.7y), categorized at Functional Ambulation Categories (FAC) 0 to 5.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Energy expenditure (measured using indirect calorimetry) expressed in METs. The recorded values were calculated for every participant and averaged for each activity: lying, supported and unsupported sitting, standing, wheelchair propulsion, and walking. Calculations were done for the total group and categorized by the FAC.

RESULTS

For the total group the mean METs ± SDs were 1.04±.11 for sitting supported, 1.09±.15 for sitting unsupported, 1.31±.25 for standing, 1.91±.42 for wheelchair propulsion, and 2.52±.55 for walking. People with stroke in all FAC had METs values >1.5 when propelling a wheelchair or walking.

CONCLUSIONS

Energy expenditure during typical sedentary behaviors (ie, sitting) is narrowly bounded at approximately 1.0 MET. Energy expenditure during sitting and standing was ≤1.5 MET for all FAC, with the exception of FAC 0 (1.6 MET during standing). Independent wheelchair propulsion and walking can be categorized as light activities (≥1.5 MET).

Resting energy expenditure adaptation after short-term caloric restriction in morbidly obese women

Objective:The objective of this study was to describe changes in the resting energy expenditure, substrate oxidation rate, and body composition in morbidly obese women subjected to short-term caloric restriction. Methods:This was a prospective study that included ten obese women with body mass index greater than 40 kg/m2 and aged between 20-50 years. The participants were hospitalized for eight days and received a controlled conventional low-calorie diet, 1200 kcal/day, for seven days. Body weight, body mass index, abdominal circumference, body composition, resting energy expenditure, and substrate oxidation rate were evaluated at the beginning and at the end of the study. Results:A significant reduction in body weight (p=0.005), body mass index (p=0.005), abdominal circumference (p=0.005), fat mass (p=0.005) and fat-free mass (p=0.008) was observed at the end of the study. There was an average reduction in resting energy expenditure of approximately 124 kcal/day (5%). Substrate oxidation rate did not show statistically significant changes. There was a positive correlation only between body weight reduction and fat-free mass reduction (r=0.753; p=0.012). Conclusion:There was an adaptive response of the resting energy expenditure with short-term energy restriction in morbidly obese women with a 5% reduction in resting energy expenditure and a positive correlation between weight loss and the fat-free mass, which indicates the influence of fat-free mass on the decrease in resting energy expenditure. Therefore, short-term caloric restriction in morbidly obese women led to a decrease in resting energy expenditure and fat-free mass, which suggests a rapid adaptation of energy expenditure.

Muscle activation and energy-requirements for varying postures in children and adolescents with cerebral palsy

OBJECTIVE

To determine energy expenditure and muscle activity among children and adolescents with cerebral palsy (CP), across several conditions that approximate sedentary behavior, and standing.

STUDY DESIGN

Subjects with spastic CP (n = 19; 4-20 years of age; Gross Motor Function Classification System Expanded and Revised [GMFCS-E&R] levels I-V) participated in this cohort study. Energy-expenditure and muscle activity were measured during lying supine, sitting with support, sitting without support, and standing. Energy-expenditure was measured using indirect calorimetry and expressed in metabolic equivalents (METs). Muscle activation was recorded using surface electromyography. The recorded values were calculated for every child and then averaged per posture.

RESULTS

Mean energy expenditure was >1.5 METs during standing for all GMFCS-E&R levels. There was a nonsignificant trend for greater muscle activation for all postures with less support. Only for children classified at GMFCS-E&R level III did standing result in significantly greater muscle activation (P < .05) compared with rest.

CONCLUSIONS

Across all GMFCS-E&R levels, children and adolescents with CP had elevated energy expenditure during standing that exceeded the sedentary threshold of 1.5 METs. Our findings suggest that changing a child's position to standing may contribute to the accumulation of light activity and reduction of long intervals of sedentary behavior.

Respiratory quotient evolution during normal pregnancy: what nutritional or clinical information can we get out of it?

Food intake increases to a varying extent during pregnancy to provide extra energy for the growing fetus. Measuring the respiratory quotient (RQ) during the course of pregnancy (by quantifying O2 consumption and CO2 production with indirect calorimetry) could be potentially useful since it gives an insight into the evolution of the proportion of carbohydrate vs. fat oxidized during pregnancy and thus allows recommendations on macronutrients for achieving a balanced (or slightly positive) substrate intake. A systematic search of the literature for papers reporting RQ changes during normal pregnancy identified 10 papers reporting original research. The existing evidence supports an increased RQ of varying magnitude in the third trimester of pregnancy, while the discrepant results reported for the first and second trimesters (i.e. no increase in RQ), explained by limited statistical power (small sample size) or fragmentary data, preclude safe conclusions about the evolution of RQ during early pregnancy. From a clinical point of view, measuring RQ during pregnancy requires not only sophisticated and costly indirect calorimeters but appears of limited value outside pure research projects, because of several confounding variables: (1) spontaneous changes in food intake and food composition during the course of pregnancy (which influence RQ); (2) inter-individual differences in weight gain and composition of tissue growth; (3) technical factors, notwithstanding the relatively small contribution of fetal metabolism per se (RQ close to 1.0) to overall metabolism of the pregnant mother.

Five-day whole-body cryostimulation, blood inflammatory markers, and performance in high-ranking professional tennis players

CONTEXT

Tournament season can provoke overreaching syndrome in professional tennis players, which may lead to deteriorated performance. Thus, appropriate recovery methods are crucial for athletes in order to sustain high-level performance and avoid injuries. We hypothesized that whole-body cryostimulation could be applied to support the recovery process.

OBJECTIVE

To assess the effects of 5 days of whole-body cryostimulation combined with moderate-intensity training on immunologic, hormonal, and hematologic responses; resting metabolic rate; and tennis performance in a posttournament season.

DESIGN

Controlled laboratory study.

SETTING

National Olympic Sport Centre.

PATIENTS OR OTHER PARTICIPANTS

Twelve high-ranking professional tennis players.

INTERVENTION(S)

Participants followed a moderate-intensity training program. A subgroup was treated with the 5-day whole-body cryostimulation (-120°C) applied twice a day. The control subgroup participated in the training only. Main Outcome Measure(s): Pretreatment and posttreatment blood samples were collected and analyzed for tumor necrosis factor α, interleukin 6, testosterone, cortisol, and creatine kinase. Resting metabolic rate and performance of a tennis drill were also assessed.

RESULTS

Proinflammatory cytokine (tumor necrosis factor α) decreased and pleiotropic cytokine (interleukin 6) and cortisol increased in the group exposed to cryostimulation. In the same group, greater stroke effectiveness during the tennis drill and faster recovery were observed. Neither the training program nor cryostimulation affected resting metabolic rate.

CONCLUSIONS

Professional tennis players experienced an intensified inflammatory response after the completed tournament season, which may lead to overreaching. Applying whole-body cryostimulation in conjunction with moderate-intensity training was more effective for the recovery process than the training itself. The 5-day exposure to cryostimulation twice a day ameliorated the cytokine profile, resulting in a decrease in tumor necrosis factor α and an increase in interleukin 6.

Consumption of low-fat dairy foods for 6 months improves insulin resistance without adversely affecting lipids or bodyweight in healthy adults: a randomized free-living cross-over study

Background

Given the highly debated role of dairy food consumption in modulating biomarkers of metabolic syndrome, this study was conducted to examine the influence of long-term (6 month) dairy consumption on metabolic parameters in healthy volunteers under free-living conditions without energy restriction.

Methods

Twenty-three healthy subjects completed a randomized, crossover trial of 12 months. Participants consumed their habitual diets and were randomly assigned to one of two treatment groups: a high dairy supplemented group instructed to consume 4 servings of dairy per day (HD); or a low dairy supplemented group limited to no more than 2 servings of dairy per day (LD). Baseline, midpoint, and endpoint metabolic responses were examined.

Results

Endpoint measurements of body weight and composition, energy expenditure, blood pressure, blood glucose, and blood lipid and lipoprotein responses did not differ (p > 0.05) between the LD and HD groups. HD consumption improved (p < 0.05) plasma insulin (-9%) and insulin resistance (-11%, p = 0.03) as estimated by HOMA-IR compared with the LD group.

Conclusions

Study results suggest that high dairy consumption (4 servings/d) may improve insulin resistance without negatively impacting bodyweight or lipid status under free-living conditions.

Trial registration

Trial registration: NCT01761955

Hypermetabolism and altered substrate oxidation in HIV-infected patients with lipodystrophy

OBJECTIVE

Human immunodeficiency virus type 1 (HIV)-associated lipodystrophy syndrome compromises body composition and produces metabolic alterations, such as dyslipidemia and insulin resistance. This study aims to determine whether energy expenditure and substrate oxidation are altered due to human HIV-associated lipodystrophy syndrome.

METHODS

We compared energy expenditure and substrate oxidation in 10 HIV-infected men with lipodystrophy syndrome (HIV+LIPO+), 22 HIV-infected men without lipodystrophy syndrome (HIV+LIPO-), and 12 healthy controls. Energy expenditure and substrate oxidation were assessed by indirect calorimetry, and body composition was assessed by dual-energy X-ray absorptiometry. The substrate oxidation assessments were performed during fasting and 30 min after eucaloric breakfast consumption (300 kcal).

RESULTS

The resting energy expenditure adjusted for lean body mass was significantly higher in the HIV+LIPO+ group than in the healthy controls (P = 0.02). HIV-infected patients had increased carbohydrate oxidation and lower lipid oxidation when compared to the control group (P < 0.05) during fasting conditions. After the consumption of a eucaloric breakfast, there was a significant increase in carbohydrate oxidation only in the HIV+LIPO- and control groups (P < 0.05), but there was no increase in the HIV+LIPO+ group.

CONCLUSION

Hypermetabolism and alteration in substrate oxidation were observed in the HIV+LIPO+ group.

Short-term carbohydrate-restricted diet for weight loss in severely obese women

BACKGROUND

Weight loss in bariatric pre-surgery period reduces surgical complications, surgery time, blood loss, and length of hospital stay. Carbohydrate-restricted diets have been used as an alternative for weight loss. We tested the efficacy of a low-calorie carbohydrate-restricted diet (RD) for short-term weight loss in women with severe obesity and evaluate its metabolic effects in relation to a conventional low-calorie diet (CD).

METHODS

The subjects received a 1,200-kcal diet with or without carbohydrate restriction for a period of 1 week in the hospital. Nineteen obesity class III women were distributed into two groups: experimental (n = 10) and control (n = 9). The following variables were assessed at the beginning and end of the study: anthropometric measurements, body composition, resting energy expenditure, substrate oxidation, and biochemical tests.

RESULTS

Compared with CD, RD led to larger weight loss (2.6 and 4.4 kg, respectively; p = 0.01) and waist circumference reduction (p < 0.01). Among the assessed biochemical indicators, only plasma and urine acetone levels were different (p < 0.01); higher values were found in the experimental group with no symptoms and other diet-related complaints. There was also a significant decrease in triglycerides and carbohydrate oxidation, as well as a significant enhancement in lipid oxidation in the RD group.

CONCLUSION

Short-term RD was more efficient than CD regarding quick weight loss and waist circumference reduction, which may favor gastroplasty. Also, RD did not lead adverse metabolic effects.

Chronic intake of fractionated yellow pea flour reduces postprandial energy expenditure and carbohydrate oxidation

Effects of dietary fibers on human postprandial energetics remain undefined. The objective of the present study was to explore effects of whole yellow pea flour (WPF) and fractionated pea flour (FPF) on postprandial energy expenditure, substrate utilization, and hepatic triglyceride synthesis rate. Using a crossover-diet controlled design, 23 overweight men and women received muffins containing WPF, FPF, and white wheat flour (WF) for 28 days, followed by 28-day washout periods. Subjects received 50 g/day WPF and WF. Given that FPF is approximately 84% fiber, the amount of FPF administered to volunteers was equivalent to the amount of pea-derived fiber in the WPF treatment. Four weeks of FPF consumption reduced (P=.007) total postprandial energy expenditure (333.0±3.6 kcal/330 minutes) compared with WF (349.3±3.6 kcal/330 minutes). When values were normalized to the level of food energy consumed, FPF (4.6±0.3%) decreased (P=.018) the thermic effect of food (TEF) compared with WF (5.7±0.3%). Carbohydrate oxidation tended to be lower (P=.075) with FPF (44.7±2.1 g/330 minutes) versus WF (51.2±0.1.9 g/330 minutes). WPF had no effect on total energy expenditure, TEF, or carbohydrate oxidation. Only after 370 minutes was cumulative oxidation of [1-(13)C]palmitic acid higher (P=.045) in the WPF group (0.96±0.05%) compared with FPF (0.81±0.05%). Neither treatment had any effect on hepatic triglyceride synthesis rate. In conclusion, chronic ingestion of different fractions of yellow peas imposes distinctive effects on postprandial energy expenditure and substrate utilization.

Bedside quantification of dead-space fraction using routine clinical data in patients with acute lung injury: secondary analysis of two prospective trials

INTRODUCTION

Dead-space fraction (Vd/Vt) has been shown to be a powerful predictor of mortality in acute lung injury (ALI) patients. The measurement of Vd/Vt is based on the analysis of expired CO2 which is not a part of standard practice thus limiting widespread clinical application of this method. The objective of this study was to determine prognostic value of Vd/Vt estimated from routinely collected pulmonary variables.

METHODS

Secondary analysis of the original data from two prospective studies of ALI patients. Estimated Vd/Vt was calculated using the rearranged alveolar gas equation: Vd/Vt=1-[(0.86×VCO2est)/(VE×PaCO2)] where VCO2est is the estimated CO2 production calculated from the Harris Benedict equation, minute ventilation (VE) is obtained from the ventilator rate and expired tidal volume and PaCO2 from arterial gas analysis. Logistic regression models were created to determine the prognostic value of estimated Vd/Vt.

RESULTS

One hundred and nine patients in Mayo Clinic validation cohort and 1896 patients in ARDS-net cohort demonstrated an increase in percent mortality for every 10% increase in Vd/Vt in a dose response fashion. After adjustment for non-pulmonary and pulmonary prognostic variables, both day 1 (adjusted odds ratio-OR = 1.07, 95%CI 1.03 to 1.13) and day 3 (OR = 1.12, 95% CI 1.06 to 1.18) estimated dead-space fraction predicted hospital mortality.

CONCLUSIONS

Elevated estimated Vd/Vt predicts mortality in ALI patients in a dose response manner. A modified alveolar gas equation may be of clinical value for a rapid bedside estimation of Vd/Vt, utilizing routinely collected clinical data.

The effects of Xanthigen in the weight management of obese premenopausal women with non-alcoholic fatty liver disease and normal liver fat

AIM

To investigate the effects of Xanthigen (brown marine algae fucoxanthin + pomegranate seed oil (PSO)) on body weight, body fat, liver lipids, and blood biochemistry; and Xanthigen and its individual components on resting energy expenditure (REE) in obese, non-diabetic female volunteers with non-alcoholic fatty liver disease (NAFLD) and normal liver fat (NLF) content.

METHODS

Sixteen-week, double-blind, randomized, placebo-controlled study. Food record data, body composition, REE (only 41 volunteers with NAFLD) and blood sample analysis were assessed weekly for 16 weeks in 151 non-diabetic, obese premenopausal women with liver fat content above 11% (NAFLD) n = 113, and below 6.5% (NLF) n = 38.

RESULTS

Xanthigen-600/2.4 mg (300 mg PSO + 300 mg brown seaweed extract containing 2.4 mg fucoxanthin) resulted in statistically significant reduction of body weight (5.5 +/- 1.4 kg NAFLD group and 4.9 +/- 1.2 kg NLF group, p < 0.05), waist circumference (NAFLD group only), body (3.5 +/- 1.9 kg NAFLD group, p < 0.001; 3.6 +/- 0.7 kg NLF group, p < 0.05) and liver fat content, liver enzymes (NAFLD group only), serum triglycerides and C-reactive protein. Weight loss and reduction in body and liver fat content occurred earlier in patients with NLF than in patients with NAFLD. Fucoxanthin (> 2.4 mg) and Xanthigen-400/1.6 mg (200 mg PSO + 200 mg brown seaweed extract containing 1.6 mg fucoxanthin) significantly increased REE in NAFLD subjects compared to placebo.

CONCLUSIONS

Xanthigen promoted weight loss, reduced body and liver fat content, and improved liver function tests in obese non-diabetic women. Xanthigen and Fucoxanthin also increased REE. This product may be considered a promising food supplement in the management of obesity.

Increased energy expenditure contributes more to the body weight-reducing effect of rimonabant than reduced food intake in candy-fed wistar rats

The CB1 receptor antagonist, rimonabant, affects the endocannabinoid system and causes a sustained reduction in body weight (BW) despite the transient nature of the reduction in food intake. Therefore, in a multiple-dose study, female candy-fed Wistar rats were treated with rimonabant (10 mg/kg) and matched with pair-fed rats to distinguish between hypophagic action and hypothesized effects on energy expenditure. Within the first week of treatment, rimonabant reduced BW nearly to levels of standard rat chow-fed rats. Evaluation of energy balance (energy expenditure measured by indirect calorimetry in relation to metabolizable energy intake calculated by bomb calorimetry) revealed that increased energy expenditure based on increased fat oxidation contributed more to sustained BW reduction than reduced food intake. A mere food reduction through pair feeding did not result in comparable effects because animals reduced their energy expenditure to save energy stores. Because fat oxidation measured by indirect calorimetry increased immediately after dosing in the postprandial state, the acute effect of rimonabant on lipolysis was investigated in postprandial male rats. Rimonabant elevated free fatty acids postprandially, demonstrating an inherent pharmacological activity of rimonabant to induce lipolysis and not secondarily postabsorptively due to reduced food intake. We conclude that the weight-reducing effect of rimonabant was due to continuously elevated energy expenditure based on increased fat oxidation driven by lipolysis from fat tissue as long as fat stores were elevated. When the amount of endogenous fat stores declined, rimonabant-induced increased energy expenditure was maintained by a re-increase in food intake.

MedGem hand-held indirect calorimeter is valid for resting energy expenditure measurement in healthy children

OBJECTIVE

To assess the validity of a new hand-held indirect calorimeter [MedGem (MG)] in the determination of resting energy expenditure (REE; kilocalories per day) in children.

RESEARCH METHODS AND PROCEDURES

One hundred male (n = 54) and female (n = 46) children (10.6 +/- 3.2 years, 43.9 +/- 19.0 kg, 146.1 +/- 18.8 cm, 19.6 +/- 4.9 kg/m(2)) participated. Children arrived at the University of Oklahoma body composition laboratory between 5:30 am and 6:15 am after an overnight fast. On arrival, subjects voided and remained quietly in the supine position for 15 minutes before testing. REE was measured by indirect calorimetry (in random order), with both the MG (sitting upright) and the criterion Delta Trac II (DT) (supine). Data are reported as the mean +/- standard deviation.

RESULTS

The mean MG REE (1452 +/- 355 kcal/d) was significantly higher than DT REE (1349 +/- 296 kcal/d, p < 0.001). Bland-Altman analysis revealed a mean bias (MG - DT) of 104 kcal/d, with limits of agreement of -241 to +449 kcal/d. To examine the difference in subject positioning, an independent sample of 38 subjects performed the MG in its normal position (sitting) and holding the MG in a supine position. REE by the MG in the sitting position (1475 +/- 350 kcal/d) was significantly (p < 0.05) higher than the MG in the supine position (1419 +/- 286 kcal/d).

DISCUSSION

The mean difference in REE between MG and DT was relatively small (103 kcal/d) but significant; however, a portion of this difference may have been related to differences in subject positioning. These preliminary data indicate that the MG shows promise as a valid tool in the assessment of REE in children.

ICAM-1 and beta2 integrin deficiency impairs fat oxidation and insulin metabolism during fasting

Intercellular adhesion molecule 1 (ICAM-1) and beta2 integrins play critical roles in immune responses. ICAM-1 may also participate in regulation of energy balance because ICAM-1-deficient mice become obese on a high-fat diet. We show that mice deficient in these adhesion receptors are unable to respond to fasting by up-regulation of fatty acid oxidation. Normal mice, when fasted, exhibit reduced circulating neutrophil counts and increased ICAM-1 expression and neutrophil recruitment in liver. Mice lacking ICAM-1 or beta2 integrins fail to show these responses--instead they become hypoglycemic with steatotic livers. Fasting ICAM-1-deficient mice reduce insulin more slowly than wild-type mice. This produces fasting hyperinsulinemia that prevents activation of adenosine mono-phosphate (AMP)-activated protein kinase in muscles and liver, which results in decreased import of long chain fatty acids into mitochondria. Thus, we show a new role for immune cells and their adhesion receptors in regulating metabolic response to fasting.

Clamp techniques in paediatrics: what have we learned?

The marked increase in conditions associated with insulin resistance in youth, including obesity, polycystic ovary syndrome, type 2 diabetes mellitus etc., has prompted the need to assess insulin sensitivity in this age group. Even though insulin resistance plays an important role in disorders of glucose metabolism and other pathological conditions, both insulin sensitivity and insulin secretion should be determined for a comprehensive evaluation of glucose homeostasis disorders. Insulin sensitivity and secretion are intricately coupled with a delicate feedback mechanism governing their relationship. This article will delineate our paediatric experience with the clamp technique, the hyperinsulinaemic-euglycaemic clamp in assessing in vivo insulin sensitivity, and the hyperglycaemic clamp in assessing insulin secretion.

Percent relative cumulative frequency analysis in indirect calorimetry: application to studies of transgenic mice

Indirect calorimetry is commonly used in research and clinical settings to assess characteristics of energy expenditure. Respiration chambers in indirect calorimetry allow measurements over long periods of time (e.g., hours to days) and thus the collection of large sets of data. Current methods of data analysis usually involve the extraction of only a selected small proportion of data, most commonly the data that reflects resting metabolic rate. Here, we describe a simple quantitative approach for the analysis of large data sets that is capable of detecting small differences in energy metabolism. We refer to it as the percent relative cumulative frequency (PRCF) approach and have applied it to the study of uncoupling protein-1 (UCP1) deficient and control mice. The approach involves sorting data in ascending order, calculating their cumulative frequency, and expressing the frequencies in the form of percentile curves. Results demonstrate the sensitivity of the PRCF approach for analyses of oxygen consumption (.VO2) as well as respiratory exchange ratio data. Statistical comparisons of PRCF curves are based on the 50th percentile values and curve slopes (H values). The application of the PRCF approach revealed that energy expenditure in UCP1-deficient mice housed and studied at room temperature (24 degrees C) is on average 10% lower (p < 0.0001) than in littermate controls. The gradual acclimation of mice to 12 degrees C caused a near-doubling of .VO2 in both UCP1-deficient and control mice. At this lower environmental temperature, there were no differences in .VO2 between groups. The latter is likely due to augmented shivering thermogenesis in UCP1-deficient mice compared with controls. With the increased availability of murine models of metabolic disease, indirect calorimetry is increasingly used, and the PRCF approach provides a novel and powerful means for data analysis.

Assessment of energy expenditure in children and adolescents

PURPOSE OF THE REVIEW

This is a review on recent studies regarding methodological aspects of assessment of energy expenditure in children and adolescents.

RECENT FINDINGS

A variety of methods used for assessment of different components of energy expenditure has been validated and used in children and adolescents. Reference values derived from representative groups of healthy children and adolescents are now available. Variations in the different components of energy expenditure and physical activity have been proposed to be associated with weight gain, and the prevalence of overweight and obesity. However, recent cross-sectional and longitudinal data in children and adolescents do not provide strong evidence for this idea. In contrast, hypermetabolism, which is frequently seen in critically ill children, may contribute to their tissue catabolism. In this case beta blockade seems to be a way to increase 'metabolic economy' and thus to reduce tissue catabolism. In chronically ill children and adolescents (e.g. patients with cystic fibrosis and sickle cell anemia) energy expenditure is also frequently increased and group specific algorithms are needed for predicting energy expenditure when measurement facilities are not available.

SUMMARY

Methods for assessment of the different components of energy expenditure have been validated in children and adolescents. The combined use of these methods together with detailed analyses of body composition is recommended for future studies. In patients with acute or chronic illness measurements of energy expenditure are necessary if disease-specific algorithms are not available.

The human body may buffer small differences in meal size and timing during a 24-h wake period provided energy balance is maintained

Because approximately 20% of the work force in the industrialized world have irregular working hours, it is pertinent to study the consequences of eating at irregular, especially nighttime hours. We studied the postprandial responses during nocturnal fasting vs. eating throughout a 24-h wake period. Seven healthy males were studied twice in a crossover design. After a 6-d diet adjustment period [high fat diet, 45 energy percent (en%) fat, 40 en% carbohydrates)] with sleep from 2300 to 0700 h, the men were kept awake for 24 h at the metabolic ward and given either 6 isoenergetic meals, i.e., every 4 h (N-eat) or 4 isoenergetic meals from 0800 to 2000 h followed by a nocturnal fast (N-fast), with the same 24-h energy intake. Energy expenditure, substrate utilization, activity, heat release, body temperature and blood variables were measured over 24 h. Energy expenditure and blood glucose, triacylglycerol, insulin and glucagon concentrations were lower and nonesterified fatty acids concentrations were higher during the nocturnal fast than during nocturnal eating (P < 0.05); however, no 24-h differences between the protocols were apparent. Nocturnal fasting slightly altered the secretory patterns of the thyroid hormones and cortisol (P < 0.05). We found no clear indication that it would be more favorable to ingest few larger daytime meals than smaller meals throughout the 24-h period. The body seems to be able to buffer small differences in meal size and timing provided energy balance is maintained.

Assessment of resting energy expenditure in mechanically ventilated patients

BACKGROUND

Usual equations for predicting resting energy expenditure (REE) are not appropriate for critically ill patients, and indirect calorimetry criteria render its routine use difficult.

OBJECTIVE

Variables that might influence the REE of mechanically ventilated patients were evaluated to establish a predictive relation between these variables and REE.

DESIGN

The REE of 70 metabolically stable, mechanically ventilated patients was prospectively measured by indirect calorimetry and calculated with the use of standard predictive models (Harris and Benedict's equations corrected for hypermetabolism factors). Patient data that might influence REE were assessed, and multivariate analysis was conducted to determine the relations between measured REE and these data. Measured and calculated REE were compared by using the Bland-Altman method.

RESULTS

Multivariate analysis retained 4 independent variables defining REE: body weight (r(2) = 0.14, P < 0.0001), height (r(2) = 0.11, P = 0.0002), minute ventilation (r(2) = 0.04, P = 0.01), and body temperature (r(2) = 0.07, P = 0.002): REE (kcal/d) = 8 x body weight + 14 x height + 32 x minute ventilation + 94 x body temperature - 4834. REE calculated with this equation was well correlated with measured REE (r(2) = 0.61, P < 0.0001). Bland-Altman plots showed a mean bias approaching zero, and the limits of agreement between measured and predicted REE were clinically acceptable.

CONCLUSION

Our results suggest that REE estimated on the basis of body weight, height, minute ventilation, and body temperature is clinically more relevant than are the usual predictive equations for metabolically stable, mechanically ventilated patients.

Measurement of the mechanical power of walking by satellite positioning system (GPS)

PURPOSE

This descriptive article illustrates the application of Global Positioning System (GPS) professional receivers in the field of locomotion studies. The technological challenge was to assess the external mechanical work in outdoor walking.

METHODS

Five subjects walked five times during 5 min on an athletic track at different imposed stride frequency (from 70-130 steps x min(-1)). A differential GPS system (carrier phase analysis) measured the variation of the position of the trunk at 5 Hz. A portable indirect calorimeter recorded breath-by-breath energy expenditure.

RESULTS

For a walking speed of 1.05 +/- 0.11 m x s(-1), the vertical lift of the trunk (43 +/- 14 mm) induced a power of 46.0 +/- 20.4 W. The average speed variation per step (0.15 +/- 0.03 m x s(-1)) produced a kinetic power of 16.9 +/- 7.2 W. As compared with commonly admitted values, the energy exchange (recovery) between the two energy components was low (39.1 +/- 10.0%), which induced an overestimated mechanical power (38.9 +/- 18.3 W or 0.60 W x kg(-1) body mass) and a high net mechanical efficiency (26.9 +/- 5.8%).

CONCLUSION

We assumed that the cause of the overestimation was an unwanted oscillation of the GPS antenna. It is concluded that GPS (in phase mode) is now able to record small body movements during human locomotion, and constitutes a promising tool for gait analysis of outdoor unrestrained walking. However, the design of the receiver and the antenna must be adapted to human experiments and a thorough validation study remains to be conducted.

Can accelerometry accurately predict the energy cost of uphill/downhill walking?

To evaluate whether an activity monitor based on body acceleration measurement can accurately assess the energy cost of the human locomotion, 12 subjects walked a combination of three different speeds (preferred speed +/- 1 km/h) and seven slopes (-15 to +15% by steps of 5%) on a treadmill. Body accelerations were recorded using a triaxial accelerometer attached to the low back. The mean of the integral of the vector magnitude (norm) of the accelerations (mIAN) was calculated. VO2 was measured using continuous indirect calorimetry. When the results were separately analysed for each incline, mIAN was correlated to VO2 (average r = 0.87, p<0.001, n = 36). VO2 was not significantly correlated to mIAN when data were globally analysed (n = 252). Large relative errors occurred when predicted VO2 (estimated from data of level walking) was compared with measured VO2 for different inclines (-53% at +15% incline, to +55% at -15% incline). It is concluded that without an external measurement of the slope, the standard method of analysis of body accelerations cannot accurately predict the energy cost of uphill or downhill walking.

Effect of diets high or low in unavailable and slowly digestible carbohydrates on the pattern of 24-h substrate oxidation and feelings of hunger in humans

BACKGROUND

The pattern of substrate utilization with diets containing a high or a low proportion of unavailable and slowly digestible carbohydrates may constitute an important factor in the control, time course, and onset of hunger in humans.

OBJECTIVE

We tested the hypothesis that isoenergetic diets differing only in their content of unavailable carbohydrates would result in different time courses of total, endogenous, and exogenous carbohydrate oxidation rates.

DESIGN

Two diets with either a high (H diet) or a low (L diet) content of unavailable carbohydrates were fed to 14 healthy subjects studied during two 24-h periods in a metabolic chamber. Substrate utilization was assessed by whole-body indirect calorimetry. In a subgroup of 8 subjects, endogenous and exogenous carbohydrate oxidation were assessed by prelabeling the body glycogen stores with [(13)C]carbohydrate. Subjective feelings of hunger were estimated with use of visual analogue scales.

RESULTS

Total energy expenditure and substrate oxidation did not differ significantly between the 2 diets. However, there was a significant effect of diet (P: = 0.03) on the carbohydrate oxidation pattern: the H diet elicited a lower and delayed rise of postprandial carbohydrate oxidation and was associated with lower hunger feelings than was the L diet. The differences in hunger scores between the 2 diets were significantly associated with the differences in the pattern of carbohydrate oxidation among diets (r = -0.67, P: = 0. 006). Exogenous and endogenous carbohydrate oxidation were not significantly influenced by diet.

CONCLUSIONS

The pattern of carbohydrate utilization is involved in the modulation of hunger feelings. The greater suppression of hunger after the H diet than after the L diet may be helpful, at least over the short term, in individuals attempting to better control their food intake.

Whole-body protein turnover and resting energy expenditure in obese, prepubertal children

BACKGROUND

Obesity is becoming more frequent in children; understanding the extent to which this condition affects not only carbohydrate and lipid metabolism but also protein metabolism is of paramount importance.

OBJECTIVE

We evaluated the kinetics of protein metabolism in obese, prepubertal children in the static phase of obesity.

DESIGN

In this cross-sectional study, 9 obese children (x +/- SE: 44+/-4 kg, 30.9+/-1.5% body fat) were compared with 8 lean (28+/-2 kg ,16.8+/-1.2% body fat), age-matched (8.5+/-0.2 y) control children. Whole-body nitrogen flux, protein synthesis, and protein breakdown were calculated postprandially over 9 h from 15N abundance in urinary ammonia by using a single oral dose of [15N]glycine; resting energy expenditure (REE) was assessed by indirect calorimetry (canopy) and body composition by multiple skinfold-thickness measurements.

RESULTS

Absolute rates of protein synthesis and breakdown were significantly greater in obese children than in control children (x +/- SE: 208+/-24 compared with 137+/-14 g/d, P < 0.05, and 149+/-20 compared with 89+/-13 g/d, P < 0.05, respectively). When these variables were adjusted for fat-free mass by analysis of covariance, however, the differences between groups disappeared. There was a significant relation between protein synthesis and fat-free mass (r = 0.83, P < 0.001) as well as between protein synthesis and REE (r = 0.79, P < 0.005).

CONCLUSIONS

Obesity in prepubertal children is associated with an absolute increase in whole-body protein turnover that is consistent with an absolute increase in fat-free mass, both of which contribute to explaining the greater absolute REE in obese children than in control children.

Energy metabolism and body temperature of barn owls fasting in the cold

Energetic adaptation to fasting in the cold has been investigated in a nocturnal raptor, the barn owl (Tyto alba), during winter. Metabolic rate and body temperature (Tb) were monitored in captive birds, (1) after acute exposure to different ambient temperatures (Ta), and (2) during a prolonged fast in the cold (4 degrees C), to take into account the three characteristic phases of body fuel utilization that occur during a long-term but reversible fast. In postabsorptive birds, metabolic rate in the thermoneutral zone was 4. 1+/-0.1 W kg-1 and increased linearly below a lower critical temperature of 23 degrees C. Metabolic rate was 70% above basal at +4 degrees C Ta. Wet thermal conductance was 0.22 W kg-1 degrees C-1. During fasting in the cold, the mass-specific resting metabolic rate decreased by 16% during the first day (phase I) and remained constant thereafter. The amplitude of the daily rhythm in Tb was only moderately increased during phase II, with a slight lowering (0. 6 degrees C) in minimal diurnal Tb, but rose markedly in phase III with a larger drop (1.4 degrees C) in minimal diurnal Tb. Refeeding the birds ended phase III and reversed the observed changes. These results indicate that diurnal hypothermia may be used in long-term fasting barn owls and could be triggered by a threshold of body lipid depletion, according to the shift from lipid to protein fuel metabolism occurring at the phase II/phase III transition. The high cost of regulatory thermogenesis and the limited use of hypothermia during fasting may contribute to the high mortality of barn owls during winter.

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.