Whole-room Indirect Calorimeter Research Articles

Evaluating Predictive Equations for Energy Requirements throughout Breast Cancer Trajectory: A Comparative Study.

Background & AimsAccurately estimating resting energy requirements is crucial for optimizing energy intake, particularly in the context of patients with varying energy needs, such as individuals with cancer. We sought to evaluate the agreement between resting energy expenditure (REE) predicted by 40 equations and that measured by reference methods in women undergoing active breast cancer treatment stage (I-IV) and post-completion (i.e., survivors). MethodsData from 4 studies were combined. REE values estimated from 40 predictive equations identified by a systematic search were compared with REE assessed by indirect calorimetry (IC) using a metabolic cart (MC-REE N=46) or a whole-room indirect calorimeter (WRIC-REE N=44). Agreement between methods was evaluated using Bland-Altman and Lin's concordance coefficient correlation (Lin's CCC). Results90 participants (24 % survivors, 61.1% had early-stage breast cancer I or II, mean age: 56.8 ± 11 years; body mass index: 28.7 ± 6.4 kg/m2) were included in this analysis. Mean MC-REE and WRIC-REE values were 1389 ± 199 kcal/day and 1506 ± 247 kcal/day, respectively. Limits of agreement were wide for all equations compared to both MC and WRIC (∼ 300kcal for both methods), including the most commonly used ones, such as Harris-Benedict and Mifflin ST. Jeor equations; none had a bias within ±10% of measured REE, and all had low agreement per Lin's CCC analysis (< 0.90). The Korth equation exhibited the best performance against WRIC and the Lvingston-Kohlstadt equation against MC. Similar patterns of bias were observed between survivors and patients and between patients with stages I-III versus IV cancer. ConclusionMost equations failed to accurately predict REE at the group level, and none were effective at the individual level. This inaccuracy has significant implications for women with or surviving breast cancer, who may experience weight gain, maintenance, or loss due to inaccurate energy needs estimations. Therefore, our research underscores the need for further efforts to improve REE estimation.

24-h energy expenditure in people with type 1 diabetes: impact on equations for clinical estimation of energy expenditure.

Type 1 diabetes (T1D) is associated with an increase in resting metabolic rate (RMR), but the impact of T1D on other components of 24-h energy expenditure (24-h EE) is not known. Also, there is a lack of equations to estimate 24-h EE in patients with T1D. The aims of this analysis were to compare 24-h EE and its components in young adults with T1D and healthy controls across the spectrum of body mass index (BMI) and derive T1D-specific equations from clinical variables. Thirty-three young adults with T1D diagnosed ≥1 year prior and 33 healthy controls matched for sex, age and BMI were included in this analysis. We measured 24-h EE inside a whole room indirect calorimeter (WRIC) and body composition with dual x-ray absorptiometry. Participants with T1D had significantly higher 24-h EE than healthy controls (T1D = 2047 ± 23 kcal/day vs control= 1908 ± 23 kcal/day; P < 0.01). We derived equations to estimate 24-h EE with both body composition (fat free mass + fat mass) and anthropometric (weight + height) models, which provided high coefficients of determination (R2 = 0.912 for both). A clinical model that did not incorporate spontaneous physical activity yielded high coefficients of determination as well (R2 = 0.897 and R2 = 0.880 for body composition and anthropometric models, respectively). These results confirm that young adults with established T1D have increased 24-h EE relative to controls without T1D. The derived equations from clinically available variables can assist clinicians with energy prescriptions for weight management in patients with T1D.

Effect of exogenous and endogenous ketones on respiratory exchange ratio and glucose metabolism in healthy subjects.

This study examined the effect of exogenous ketone bodies (KB) on oxygen consumption (V̇o2), carbon dioxide production (V̇co2), and glucose metabolism. The data were compared with the effects of endogenous ketonemia during both, a ketogenic diet or fasting. Eight healthy individuals [24.1 ± 2.5 yr, body mass index (BMI) 24.3 ± 3.1 kg/m2] participated in a crossover intervention study and were studied in a whole-room indirect calorimeter (WRIC) to assess macronutrient oxidation following four 24-h interventions: isocaloric controlled mixed diet (ISO), ISO supplemented with ketone salts (38.7 g of β-hydroxybutyrate/day, EXO), isocaloric ketogenic diet (KETO), and total fasting (FAST). A physical activity level of 1.65 was obtained. In addition to plasma KB, 24-h C-peptide and KB excretion rates in the urine and postprandial glucose and insulin levels were measured. Although 24-h KB excretion increased in response to KETO and FAST, there was a modest increase in response to EXO only (P < 0.05). When compared with ISO, V̇o2 significantly increased in KETO (P < 0.01) and EXO (P < 0.001), whereas there was no difference in FAST. V̇co2 increased in EXO but decreased in KETO (both P < 0.01) and FAST (P < 0.001), resulting in 24-h respiratory exchange ratios (RER) of 0.828 ± 0.024 (ISO) and 0.811 ± 0.024 (EXO) (P < 0.05). In response to EXO there were no differences in basal and postprandial glucose and insulin levels, as well as in insulin sensitivity. When compared with ISO, EXO, and KETO, FAST increased homeostatic model assessment β-cell function (HOMA-B) (all P < 0.05). In conclusion, at energy balance exogenous ketone salts decreased respiratory exchange ratio without affecting glucose tolerance.NEW & NOTEWORTHY Our findings revealed that during isocaloric nutrition, additional exogenous ketone salts increased V̇o2 and V̇co2 while lowering the respiratory exchange ratio (RER). Ketone salts had no effect on postprandial glucose metabolism.

Age-related Differences In Substrate Oxidation During 24 Hours In A Whole-room Indirect Calorimeter

Age-related Differences In Substrate Oxidation During 24 Hours In A Whole-room Indirect Calorimeter

Greater anhedonia scores in healthy individuals are associated with less decline in 24-hour energy expenditure with fasting: Evidence for a link between behavioral traits and spendthrift phenotype

Obesity rates are increasing and affecting mental health. It is important to understand how behavioral traits such as anhedonia are associated with physiologic traits that may predict weight-change in clinical and non-clinical populations. We studied whether 24-hour energy expenditure (24hEE) changes with fasting and overfeeding are associated with anhedonia in a healthy cohort. We performed behavioral assessments (physical anhedonia scale (PAS) and inventory for depressive symptoms (IDS)) followed by measures of 24hEE and urinary catecholamines in a whole-room indirect calorimeter (respiratory chamber) during energy balance, and then randomly during fasting and 2 different overfeeding diets. Participants (n=98) were medically healthy, between 18 and 55 years of age, with normal glucose regulation and weight-stable 6 months before admission. Women were premenopausal and not pregnant. Higher PAS was significantly associated with lesser decrease in 24hEE with fasting and higher urinary catecholamine excretion rates – consistent with spendthrift metabolism. As IDS increased, the association between anhedonia and the change in 24hEE from energy balance to fasting decreased (B-values were lower for change in EE). Here, higher PAS scores may reflect the ability to respond with appropriate homeostatic reactions which balance energy needs. IDS scores blunting this response may explain how anhedonia and depression can lead to weight gain.

1634-P: Brown Adipose Tissue and Muscle Responses to Tolerable Cold in Black and White Young Lean Men

There has been a renewed interest in brown adipose tissue (BAT) as a therapeutic target for diabetes and obesity treatments due to its ability to consume glucose and expend energy in response to cold temperatures and Beta-adrenergic stimulation. However, comparisons of BAT in different races are limited. To address this knowledge gap, we directly compared healthy, young, lean Black and White men in a controlled inpatient study using a whole-room indirect calorimeter. 12 Black and 12 White men completed a 6-13-day protocol with randomized calorimeter temperatures between 18-31°C for 5 hours. Resting metabolic rate (RMR) was measured under reclined, fasted conditions with standard clothing. Body composition was measured by dual x-ray absorptiometry and BAT and muscle glucose uptake activity was quantified using 18-F Fluorodeoxyglucose (18-F FDG) PET-CT following the last chamber study where each individual's coldest tolerable temperature (Tct) was used. Basal metabolic rate (BMR) was defined as minimum RMR and the cold-induced thermogenesis (CIT) was calculated as the percentage increase of RMR above BMR in the cold. The groups were similar in age (23.8±4.7 yrs) and BMI (23.1±1.5 kg/m2) and their Tct (21.0±1.4°C; p=0.54) and CIT (12.1±8.1 kcal/h; p=0.8) were not different. While White males had significantly higher BAT volume (334 ± 188mL vs 242 ± 89mL; p=0.045), BAT volume was comparable between the groups after normalizing to body volume. BAT activity was similar between the groups. Among all muscle activity measured, the intercostal muscles in the Black males had significantly higher activity (p=0.002) and activity was present in all 12 Black participants but only 4 of 12 White males. Individual BAT or muscle activity did not correlate with each other nor with Tct or CIT. Our data suggest that the cold-induced BAT activity was comparable in Black and White young, lean men. The surprising difference in intercostal muscle activity warrants further investigation. Disclosure R.J.Thomas: None. R.Brychta: None. A.B.Courville: None. S.Mcgehee: None. A.M.Cypess: None. K.Y.Chen: None.

Total energy expenditure assessed by 24-h whole-room indirect calorimeter in patients with colorectal cancer: baseline findings from the PRIMe study

BackgroundTotal energy expenditure (TEE) determines energy requirements, but objective data in patients with cancer are limited. ObjectivesWe aimed to characterize TEE, investigate its predictors, and compare TEE with cancer-specific predicted energy requirements. MethodsThis cross-sectional analysis included patients with stages II–IV colorectal cancer from the Protein Recommendation to Increase Muscle (PRIMe) trial. TEE was assessed by 24-h stay in a whole-room indirect calorimeter before dietary intervention and compared with cancer-specific predicted energy requirements (25–30 kcal/kg). Generalized linear models, paired-samples t tests, and Pearson correlation were applied. ResultsThirty-one patients (56 ± 10 y; body mass index [BMI]: 27.9 ± 5.5 kg/m2; 68% male) were included. Absolute TEE was higher in males (mean difference: 391 kcal/d; 95% CI: 167, 616 kcal/d; P < 0.001), patients with colon cancer (mean difference: 279 kcal/d; 95% CI: 73, 485 kcal/d; P = 0.010), and patients with obesity (mean difference: 393 kcal/d; 95% CI: 182, 604 kcal/d; P < 0.001). Appendicular lean soft tissue (β: 46.72; 95% CI: 34.27, 59.17; P < 0.001) and tumor location (colon—β: 139.69; 95% CI: 19.44, 259.95; P = 0.023) independently predicted TEE when adjusted for sex. Error between measured TEE and energy requirements predicted by 25 kcal/kg (mean difference: 241 kcal/d; 95% CI: 76, 405 kcal/d; P = 0.010) or 30 kcal/kg (mean difference: 367 kcal/d; 95% CI: 163, 571 kcal/d; P < 0.001) was higher for patients with obesity, and proportional error was observed (25 kcal/kg: r = −0.587; P < 0.001; and 30 kcal/kg: r = −0.751; P < 0.001). TEE (mean difference: 25 kcal/kg; 95% CI: 24, 27 kcal/kg) was below predicted requirements using 30 kcal/kg (−430 ± 322 kcal/d; P < 0.001). ConclusionsThis is the largest study to assess TEE of patients with cancer using whole-room indirect calorimeter and highlights the need for improved assessment of energy requirements in this population. Energy requirements predicted using 30 kcal/kg overestimated TEE by 1.44 times in a controlled sedentary environment and TEE was outside of the predicted requirement range for most. Special considerations are warranted when determining TEE of patients with colorectal cancer, such as BMI, body composition, and tumor location.This is a baseline cross-sectional analysis from a clinical trial registered at clinicaltrials.gov as NCT02788955 (https://clinicaltrials.gov/ct2/show/NCT02788955).

0250 In-laboratory and at-home sleep assessments using wrist actigraphy in healthy individuals

Abstract Introduction Whole-room indirect calorimetry is the gold standard to measure metabolism during sleep. However, it is unknown whether sleep in a room calorimeter is reflective of a person’s natural sleep pattern or whether it suffers from limitations common to other in-laboratory assessments, such as the “first night effect”. To address this knowledge gap, we compared actigraphy-assessed sleep parameters measured in a room calorimeter with those measured at home to examine how research environments may alter natural sleep quality and patterns. Methods Ten healthy individuals (4 females; 41.5 ± 14.5 years old; 25.4 ± 4.2kg/m2) participated in the study (NCT02669212). Participants had no major sleep disturbances (Pittsburgh Sleep Quality Index; PSQI &amp;lt; 5) with minimal anxiety (0-7), assessed using the Beck Anxiety Index. The in-laboratory portion of the study was conducted in a whole-room indirect calorimeter with controlled diets and ambient temperatures. The out-patient, at home study was conducted for seven consecutive nights, further divided into weekday and weekend sleep for analysis. Sleep was measured with an ActiGraph wGT3X-BT accelerometer on the non-dominant wrist throughout the study. Results The in-laboratory total sleep time (TST) was 399.7 ± 85.7min, comparable to weekend sleep at home, which was 399.8 ± 57.6min (p=0.998). In-laboratory TST was slightly longer than weekday sleep at home (359.7 ± 69.3min), but was not significantly different (p=0.34). Sleep efficiency in all three conditions was similar for baseline (90.6 ± 6.3%), weekday (91.4 ± 4.5%), and weekend sleep at home (91.1 ± 4.9%). These results suggest that despite being in the laboratory, sleep in healthy individuals was not significantly affected by sleeping in the calorimeter. As expected, seven consecutive nights of sleep at home revealed a tendency for shorter total sleep time during the week (359.7 ± 69.3min) compared to the weekend (399.8 ± 57.6min) (p=0.095), suggesting the presence of social jetlag and circadian misalignment throughout the week. Conclusion The present study showed that actigraphy-measured sleep was not affected by sleeping in the whole-room indirect calorimeter in healthy individuals. Further studies would be crucial to address whether this trend holds for other study populations. Support (if any)

Validity and reproducibility of a whole-room indirect calorimeter for the estimation of VO2 , VCO2 , and resting metabolic rate.

Whole-room indirect calorimeters (WRICs) provide accurate instruments for the measurement of respiratory exchange, energy expenditure, and macronutrient oxidation. Here, we aimed to determine the validity and reproducibility of a 7500 L WRIC for the measurement of ventilation rates and resting metabolic rate (RMR). Technical validation was performed with propane combustion tests (n = 10) whereas biological reproducibility was tested in healthy subjects (13 women, 6 men, mean ± SD age 39.6 ± 15.3) in two 60 min measurements separated by 24 h. Subjects followed a run-in protocol prior to measurements. The coefficient of variation (CV) and intraclass correlation coefficient (ICC) were calculated for ventilation rates of O2 (VO2), CO2 (VCO2), the respiratory quotient (RQ; VCO2/VO2), and RMR. Technical validation showed good validity with CVs ranging from 0.67% for VO2 to 1.00% for energy expenditure. For biological reproducibility, CVs were 2.89% for VO2 ; 2.67% for VCO2 ; 1.95% for RQ; and 2.68% for RMR. With the exception of RQ (74%), ICCs were excellent for VO2 (94%), VCO2 (96%) and RMR (95%). Excluding participants that deviated from the run-in protocol did not alter results. In conclusion, the 7500 L WRIC is technically valid and reproducible for ventilation rates and RMR.

Exercise Timing Matters for Glycogen Metabolism and Accumulated Fat Oxidation over 24 h

Due to increasingly diverse lifestyles, exercise timings vary between individuals: before breakfast, in the afternoon, or in the evening. The endocrine and autonomic nervous systems, which are associated with metabolic responses to exercise, show diurnal variations. Moreover, physiological responses to exercise differ depending on the timing of the exercise. The postabsorptive state is associated with greater fat oxidation during exercise compared to the postprandial state. The increase in energy expenditure persists during the post-exercise period, known as "Excess Post-exercise Oxygen Consumption". A 24 h evaluation of accumulated energy expenditure and substrate oxidation is required to discuss the role of exercise in weight control. Using a whole-room indirect calorimeter, researchers revealed that exercise performed during the postabsorptive state, but not during the postprandial state, increased accumulated fat oxidation over 24 h. The time course of the carbohydrate pool, as estimated by indirect calorimetry, suggests that glycogen depletion after postabsorptive exercise underlies an increase in accumulated fat oxidation over 24 h. Subsequent studies using 13C magnetic resonance spectroscopy confirmed that the variations in muscle and liver glycogen caused by postabsorptive or postprandial exercise were consistent with indirect calorimetry data. These findings suggest that postabsorptive exercise alone effectively increases 24 h fat oxidation.

Measurement of 24-h continuous human CH4 release in a whole room indirect calorimeter.

We describe the technology and validation of a new whole room indirect calorimeter (WRIC) methodology to quantify volume of methane (VCH4) released from the human body over 24 h concurrently with the assessment of energy expenditure and substrate utilization. The new system extends the assessment of energy metabolism by adding CH4, a downstream product of microbiome fermentation that could contribute to energy balance. Our new system consists of an established WRIC combined with the addition of off-axis integrated-cavity output spectroscopy (OA-ICOS) to measure CH4 concentration ([CH4]). Development, validation, and reliability of the system included environmental experiments to measure the stability of the atmospheric [CH4], infusing CH4 into the WRIC and human cross-validation studies comparing [CH4] quantified by OA-ICOS and mid-infrared dual-comb spectroscopy (MIR DCS).Our infusion data indicated that the system measured 24-h [CH4] and VCH4 with high sensitivity, reliability, and validity. Cross-validation studies showed good agreement between OA-ICOS and MIR DCS technologies (r = 0.979, P < 0.0001). Human data revealed 24-h VCH4 was highly variable between subjects and within/between days. Finally, our method to quantify VCH4 released by breath or colon suggested that over 50% of the CH4 was eliminated through the breath. The method allows, for the first time, measurement of 24-h VCH4 (in kcal) and therefore the measurement of the proportion of human energy intake fermented to CH4 by the gut microbiome and released via breath or from the intestine; also, it allows us to track the effects of dietary, probiotic, bacterial, and fecal microbiota transplantation on VCH4.NEW & NOTEWORTHY This is the first time that continuous assessment of CH4 is reported in parallel with measurements of O2 consumption and CO2 production inside a whole room indirect calorimeter in humans and over 24 h. We provide a detailed description of the whole system and its parts. We carried out studies of reliability and validity of the whole system and its parts. CH4 is released in humans during daily activities.

Closed-loop control of air supply to whole-room indirect calorimeters to improve accuracy and standardize measurements during 24-hour dynamic metabolic studies.

The aimof this study was to test proportional-integral-derivative (PID) control of air inflow rate in a whole-room indirect calorimeter to improve accuracy in measuring oxygen (O2 ) consumption ( ) and carbon dioxide (CO2 ) production ( ). A precision gas blender infused nitrogen (N2 ) and CO2 into the calorimeter over 24 hours based on static and dynamic infusion profiles mimicking and patterns during resting and non-resting conditions. Constant (60 L/min) versus time-variant flow set by a PID controller based on the CO2 concentration was compared based on errors between measured versus expected values for respiratory exchange ratio, and metabolic rate. Compared with constant inflow, the PID controller allowed both a faster rise time and long-term maintenance of a stable CO2 concentration inside the calorimeter, resulting in more accurate estimates (mean hourly error, PID: -0.9%, 60 L/min=-2.3%, p < 0.05) during static infusions. During dynamic infusions mimicking exercise sessions, the PID controller achieved smaller errors for (mean: -0.6% vs. -2.7%, p=0.02) and respiratory exchange ratio (mean: 0.5% vs. -3.1%, p=0.02) compared with constant inflow conditions, with similar (p=0.97) and metabolic rate (p=0.76) errors. PID control in a whole-room indirect calorimeter system leads to more accurate measurements of substrate oxidation during dynamic metabolic studies.

Effects of Short-term Fasting on Ghrelin/GH/IGF-1 Axis in Healthy Humans: The Role of Ghrelin in the Thrifty Phenotype.

A greater decrease in 24-hour energy expenditure (24hEE) during short-term fasting is indicative of a thrifty phenotype. As ghrelin and the growth hormone (GH)/insulin-like growth factor 1 (IGF-1) axis are implicated in the regulation of energy intake and metabolism, we investigated whether ghrelin, GH, and IGF-1 concentrations mediate the fasting-induced decrease in 24hEE that characterizes thriftiness. In 47 healthy individuals, 24hEE was measured in a whole-room indirect calorimeter both during 24-hour eucaloric and fasting conditions. Plasma total ghrelin, GH, and IGF-1 concentrations were measured by enzyme-linked immunosorbent assay after an overnight fast the morning before and after each 24-hour session. During 24-hour fasting, on average 24hEE decreased by 8.0% (P < .001), GH increased by ~5-fold (P < .001), whereas ghrelin (mean +23 pg/mL) and IGF-1 were unchanged (both P ≥ .19) despite a large interindividual variability in ghrelin change (SD 150 pg/mL). Greater fasting-induced increase in ghrelin was associated with a greater decrease in 24hEE during 24-hour fasting (r = -0.42, P = .003), such that individuals who increased ghrelin by 200 pg/mL showed an average decrease in 24hEE by 55 kcal/day. Short-term fasting induced selective changes in the ghrelin/GH/IGF-1 axis, specifically a ghrelin-independent GH hypersecretion that did not translate into increased IGF-1 concentrations. Greater increase in ghrelin after 24-hour fasting was associated with greater decrease in 24hEE, indicating ghrelin as a novel biomarker of increased energy efficiency of the thrifty phenotype.

The counterbalancing effects of energy expenditure on body weight regulation: Orexigenic versus energy-consuming mechanisms.

ObjectiveWeight change is a dynamic function of whole‐body energy balance resulting from the interplay between energy intake and energy expenditure (EE). Recent reports have provided evidence for the existence of a causal effect of EE on energy intake, suggesting that increased EE may drive overeating, thereby promoting future weight gain. This study investigated the relationships between ad libitum energy intake and 24‐hour EE (24‐h EE) in sedentary conditions versus long‐term, free‐living weight change using a mediation analysis framework.MethodsNative American individuals (n = 61, body fat by dual‐energy x‐ray absorptiometry: 39.7% [SD 9.5%]) were admitted to the clinical inpatient unit and had baseline measurements as follows: 1) 24‐h EE accurately measured in a whole‐room indirect calorimeter during energy balance and weight stability; and 2) ad libitum energy intake objectively assessed for 3 days using computerized vending machines. Free‐living weight change was assessed after a median follow‐up time of 1.7 years (interquartile range: 1.2‐2.9).ResultsThe total effect of 24‐h EE on weight change (−0.23 kg per 100‐kcal/d difference in EE at baseline) could be partitioned into the following two independent and counterbalanced effects: higher EE protective against weight gain (−0.46 kg per 100‐kcal/d difference in EE at baseline) and an orexigenic effect promoting overeating, thereby favoring weight gain (+0.23 kg per 100‐kcal/d difference in EE at baseline).ConclusionsThe overall impact of EE on body weight regulation should be evaluated by also considering its collateral effect on energy intake. Any weight loss intervention aimed to induce energy deficits by increasing EE should take into account any potential orexigenic effects that promote compensatory overeating, thereby limiting the efficacy of these obesity therapies.

Twenty-four hour assessments of substrate oxidation reveal differences in metabolic flexibility in type 2 diabetes that are improved with aerobic training.

The aim of this study was to assess metabolic flexibility (MetFlex) in participants with type 2 diabetes within the physiologically relevant conditions of sleeping, the post-absorptive (fasting) state and during meals using 24h whole-room indirect calorimetry (WRIC) and to determine the impact of aerobic training on these novel features of MetFlex. Normal-weight, active healthy individuals (active; n = 9), obese individuals without type 2 diabetes (ND; n = 9) and obese individuals with type 2 diabetes (n = 23) completed baseline metabolic assessments. The type 2 diabetes group underwent a 10week supervised aerobic training intervention and repeated the metabolic assessments. MetFlex was assessed by indirect calorimetry in response to insulin infusion and during a 24h period in a whole-room indirect calorimeter. Indices of MetFlex evaluated by WRIC included mean RQ and RQ kinetic responses after ingesting a standard high-carbohydrate breakfast (RQBF) and sleep RQ (RQsleep). Muscle mitochondrial energetics were assessed in the vastus lateralis muscle in vivo and ex vivo using 31P-magnetic resonance spectroscopy and high-resolution respirometry, respectively. The three groups had significantly different RQsleep values (active 0.823 ± 0.04, ND 0.860 ± 0.01, type 2 diabetes 0.842 ± 0.03; p < 0.05). The active group had significantly faster RQBF and more stable RQsleep responses than the ND and type 2 diabetes groups, as demonstrated by steeper and flatter slopes, respectively. Following the training intervention, the type 2 diabetes group displayed significantly increased RQBF slope. Several indices of RQ kinetics had significant associations with in vivo and ex vivo muscle mitochondrial capacities. Twenty-four hour WRIC revealed that physiological RQ responses exemplify differences in MetFlex across a spectrum of metabolic health and correlated with skeletal muscle mitochondrial energetics. Defects in certain features of MetFlex were improved with aerobic training, emphasising the need to assess multiple aspects of MetFlex and disentangle insulin resistance from MetFlex in type 2 diabetes. ClinicalTrials.gov NCT01911104. This study was funded by the ADA (grant no. 7-13-JF-53).

Reliability of measurements of energy expenditure and substrate oxidation using whole-room indirect calorimetry.

This analysis aimed to measure the intraparticipant reliability-the intraclass correlation coefficient-of all the components of daily energy expenditure (EE) (24-hour EE, sleep EE, resting EE, basal EE, and thermic effect of food) over a period of 3 consecutive days in 35 study participants. The components of daily EE and substrate use (respiratory exchange ratio) were measured over 3 consecutive days before and after a 3-week 1,000-kcal/d caloric restriction/weight-loss intervention. There was a high degree of reliability for sleep EE (96.8%), 24-hour EE (97.8%), basal EE (90.6%), and resting EE (93.2%) during the run-in period. The intraclass correlation coefficient for the follow-up period after weight loss (3.67 ± 1.10 kg) remained high for sleep EE (95.6%), 24-hour EE (100%), basal EE (96.1%), and resting EE (92.5%). The minimal detectable differences in EE were reduced by 30% for both 24-hour EE and sleep EE when comparing 2 days versus 1 day spent in the whole-room indirect calorimeter. The reliability of the daily components of EE is very high both prior to and after a weight-loss intervention. We here provide instrumental data for investigators to adequately power studies investigating energy metabolism using whole-room indirect calorimetry.

Diurnal variations of brown fat thermogenesis and fat oxidation in humans

Background/objectivesDisturbed circadian rhythm is associated with an increased risk of obesity and metabolic disorders. Brown adipose tissue (BAT) is a site of nonshivering thermogenesis (NST) and plays a role in regulating whole-body energy expenditure (EE), substrate metabolism, and body fatness. In this study, we examined diurnal variations of NST in healthy humans by focusing on their relation to BAT activity.MethodsForty-four healthy men underwent 18F-fluoro-2-deoxy-D-glucose positron emission tomography and were divided into Low-BAT and High-BAT groups. In STUDY 1, EE, diet-induced thermogenesis (DIT), and fat oxidation (FO) were measured using a whole-room indirect calorimeter at 27 °C. In STUDY 2, EE, FO, and skin temperature in the region close to BAT depots (Tscv) and in the control region (Tc) were measured at 27 °C and after 90 min cold exposure at 19 °C in the morning and in the evening.ResultsIn STUDY 1, DIT and FO after breakfast was higher in the High-BAT group than in the Low-BAT group (P < 0.05), whereas those after dinner were comparable in the two groups. FO in the High-BAT group was higher after breakfast than after dinner (P < 0.01). In STUDY 2, cold-induced increases in EE (CIT), FO, and Tscv relative to Tc in the morning were higher in the High-BAT group than in the Low-BAT group (P < 0.05), whereas those after dinner were comparable in the two groups. CIT in the High-BAT group tended to be higher in the morning than in the evening (P = 0.056).ConclusionBAT-associated NST and FO were evident in the morning, but not in the evening, suggesting that the activity of human BAT is higher in the morning than in the evening, and thus may be involved in the association of an eating habit of breakfast skipping with obesity and related metabolic disorders.

Reduced metabolic efficiency in sedentary eucaloric conditions predicts greater weight regain in adults with obesity following sustained weight loss.

BackgroundSuccessful long-term weight loss maintenance after caloric restriction (CR) is rarely achieved. Besides known metabolic, behavioral, and cognitive factors, 24-hour energy expenditure (24hEE) relative to body size (i.e., metabolic efficiency) might influence subsequent weight loss maintenance.MethodsEleven participants with obesity (BMI=39.0±8.7 kg/m2, body fat=36.1±6.4%) had 24hEE measured in a whole-room indirect calorimeter during eucaloric conditions and weight stability prior to starting a 6-week inpatient CR study (50% of daily energy needs). Twenty-four-hour energy expenditure was adjusted via regression analysis for fat free mass (FFM) and fat mass (FM) by DXA. Body composition was reassessed at the end of CR and after 1-year follow-up. Free-living weight was assessed by monthly weight measurements during 12 months.ResultsAfter 6-week CR, participants lost 8.5±2.7% weight (FFM: −6.3±3.6 kg, FM: −3.4±1.2 kg) but regained 5.1±8.0% one year following CR, which was mostly due to FFM regain (+5.7±5.5 kg) and unchanged FM. A relatively higher 24hEE by 100 kcal/day prior to CR was associated with an average greater rate of weight regain by +0.3 kg/month during follow-up and a greater final weight regain by +5.1 kg after 1 year of follow-up.ConclusionThese results suggest that reduced metabolic efficiency in 24hEE during eucaloric, sedentary conditions may predict greater weight regain after CR-induced weight loss.

Reduced brown adipose tissue activity during cold exposure is a metabolic feature of the human thrifty phenotype

BackgroundWe recently demonstrated that thrifty subjects, characterized by a greater decrease in 24 h energy expenditure (24hEE) during short-term fasting, have less capacity for cold-induced thermogenesis (CIT) during 24 h of mild cold exposure. ObjectiveAs cold-induced brown adipose tissue activation (CIBA) is a determinant of CIT, we sought to investigate whether thrifty individuals also have reduced CIBA. MethodsTwenty-four healthy subjects (age: 29.8 ± 9.5y, body fat: 27.3 ± 12.4%, 63% male) were admitted to our clinical research unit and underwent two 24hEE assessments in a whole-room indirect calorimeter during energy balance and fasting conditions at thermoneutrality to quantify their degree of thriftiness. Positron emission tomography/computed tomography scans were performed after exposure to 16 °C for 2 h to quantify peak CIBA. ResultsA greater decrease in 24hEE during fasting was associated with lower peak CIBA (r = 0.50, p = 0.01), such that a 100 kcal/day greater reduction in 24hEE related to an average 3.2 g/mL lower peak CIBA. ConclusionOur results indicate that reduced CIBA is a metabolic trait of the thrifty phenotype which might explain reduced CIT capacity and greater predisposition towards weight gain in individuals with a thrifty metabolism.

Room Indirect Calorimetry Operating and Reporting Standards (RICORS 1.0): A Guide to Conducting and Reporting Human Whole-Room Calorimeter Studies.

Whole-room indirect calorimeters have been used to study human metabolism for more than a century. These studies have contributed substantial knowledge to the assessment of nutritional needs and the regulation of energy expenditure and substrate oxidation in humans. However, comparing results from studies conducted at different sites is challenging because of a lack of consistency in reporting technical performance, study design, and results. In May 2019, an expert panel was convened to consider minimal requirements for conducting and reporting the results of human whole-room indirect calorimeter studies. We propose Room Indirect Calorimetry Operating and Reporting Standards, version 1.0 (RICORS 1.0) to provide guidance to ensure consistency and facilitate meaningful comparisons of human energy metabolism studies across publications, laboratories, and clinical sites.