Total daily energy expenditure (“total expenditure”) reflects daily energy needs and is a critical variable in human health and physiology, but its trajectory over the life course is poorly studied. We analyzed a large, diverse database of total expenditure measured by the doubly labeled water method for males and females aged 8 days to 95 years. Total expenditure increased with fat-free mass in a power-law manner, with four distinct life stages. Fat-free mass–adjusted expenditure accelerates rapidly in neonates to ~50% above adult values at ~1 year; declines slowly to adult levels by ~20 years; remains stable in adulthood (20 to 60 years), even during pregnancy; then declines in older adults. These changes shed light on human development and aging and should help shape nutrition and health strategies across the life span.

Weight loss results in adaptive thermogenesis, and there is no indication for a change in adaptive thermogenesis up to 1 y, when weight loss is maintained. This trial was registered at clinicaltrials.gov as NCT01015508.

Summary The doubly labeled water (DLW) method measures total energy expenditure (TEE) in free-living subjects. Several equations are used to convert isotopic data into TEE. Using the International Atomic Energy Agency (IAEA) DLW database (5,756 measurements of adults and children), we show considerable variability is introduced by different equations. The estimated rCO 2 is sensitive to the dilution space ratio (DSR) of the two isotopes. Based on performance in validation studies, we propose a new equation based on a new estimate of the mean DSR. The DSR is lower at low body masses (<10 kg). Using data for 1,021 babies and infants, we show that the DSR varies non-linearly with body mass between 0 and 10 kg. Using this relationship to predict DSR from weight provides an equation for rCO 2 over this size range that agrees well with indirect calorimetry (average difference 0.64%; SD = 12.2%). We propose adoption of these equations in future studies.

Capsinoids only increased EE in BAT-positive participants, which suggests that BAT mediates EE evoked by capsinoids. This implies that capsinoids stimulate BAT to a lesser degree than cold exposure as evidenced by 18F-FDG uptake below the presently accepted SUV thresholds defining BAT activation. This trial was registered at www.clinicaltrials.gov as NCT02964442.

Sleep duration benefits from weight loss or vice versa. Successful weight loss, loss of body fat, and 3-mo weight maintenance in short and average sleepers are underscored by an increase in sleep duration or vice versa. This trial was registered at clinicaltrials.gov as NCT01015508.

Highlights d Energy compensation in humans was analyzed from daily and basal energy expenditure d Reduced BEE results in energy compensation of 28% d Degree of energy compensation varied between people of different body composition

Objective This study aimed to compare the associations of positron emission tomography (PET), magnetic resonance (MR), and infrared thermography (IRT) imaging modalities with energy expenditure (EE) after brown adipose tissue (BAT) activation using capsinoid ingestion and cold exposure. Methods Twenty participants underwent PET‐MR, IRT imaging, and whole‐body calorimetry after capsinoid ingestion and cold exposure. Standardized uptake values (SUV) and the fat fraction (FF) of the supraclavicular brown adipose tissue regions were estimated. The anterior supraclavicular temperature (Tscv) from IRT at baseline and postintervention was measured. Two‐hour post–capsinoid ingestion EE and post–cold exposure EE served as a reference to correlate fluorodeoxyglucose uptake, FF, and Tscv for BAT assessment. IRT images were geometrically transformed to overlay on PET‐MR for visualization of the hottest regions. Results The supraclavicular hot spot identified on IRT closely corresponded to the area of maximal fluorodeoxyglucose uptake on PET images. Controlling for body weight, post–cold exposure Tscv was a significant variable associated with EE (P = 0.025). The SUV was significantly inversely correlated with FF (P = 0.012) and significantly correlated with peak of Tscv during cold exposure in BAT‐positive participants (P = 0.022). Conclusions Tscv correlated positively with EE and was also significantly correlated with SUV after cold exposure. Both IRT and MR FF are promising methods to study BAT activity noninvasively.

Background: Weight loss due to a negative energy balance is considered to be accompanied by a decrease in physical activity. Objective: The aim of this study was to investigate whether a decrease in physical activity is sustained during weight maintenance. Design: Subjects were 20 men and 31 women [mean (6SD) age: 42 6 8 y; BMI (in kg/m 2 ): 31.4 6 2.8]. Weight loss was achieved by an 8-wk very-low-energy diet period, followed by 44 wk of weight maintenance. Physical activity measures were total energy expenditure expressed as a multiple of sleeping metabolic rate (PAL SMR ) and resting metabolic rate (PAL RMR ), activity-induced energy expenditure divided by body weight (AEE/kg), and activity counts measured by a triaxial accelerometer. Measurements took place at 0, 8, and 52 wk. Results: Body mass decreased significantly during the diet period (10.5 6 3.8%, P , 0.001), and this reduction was sustained after 52 wk (6.0 6 5.1%, P , 0.001). PAL SMR and PAL RMR decreased from 1.81 6 0.23 and 1.70 6 0.22, respectively, before the diet to 1.69 6 0.20 and 1.55 6 0.19 after the diet (P , 0.001) and increased again after weight maintenance to 1.85 6 0.27 and 1.71 6 0.23, respectively, compared with 8-wk measurements (P , 0.001). AEE/kg decreased from 0.043 6 0.015 MJ/kg at baseline to 0.037 6 0.014 MJ/kg after the diet (P , 0.001) and was higher after 52 wk (0.044 6 0.17 MJ/kg) compared with after 8 wk (P , 0.001). Activity counts decreased from 1.64 6 0.37 megacounts/d at baseline to 1.54 6 0.35 megacounts/d after the diet (P , 0.05) and were higher after 52 wk (1.73 6 0.49 megacounts/d) compared with 8 wk (P , 0.01). Conclusion: A weight loss-induced reduction in physical activity returns to baseline values when weight loss is maintained. This trial was registered at clinicaltrials.gov as NCT01015508.Am J Clin Nutr 2013;98:917-23.