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BACKGROUND: A metabolic adaptation, defined as an increase in energy expenditure (EE) beyond what is expected with weight gain during overfeeding (OF), has been reported but also refuted. Much of the inconsistency stems from the difficulty in conducting large, well-controlled OF studies in humans. OBJECTIVES: The primary aim of this study was to determine whether a metabolic adaptation to OF exists and if so, attenuates weight gain. METHODS: Thirty-five young adults consumed 40% above their baseline energy requirements for 8 wk, and sleeping metabolic rate (SMR) and 24-h sedentary energy expenditure (24h-EE) were measured before and after OF. Subjects were asked to return for a 6-mo post-OF follow-up visit to measure body weight, body composition, and physical activity. RESULTS: After adjusting for gains in fat-free mass and fat mass, SMR increased by 43 ± 123 kcal/d more than expected (P = 0.05) and 24h-EE by 23 ± 139 kcal/d (P = 0.34), indicating an overall lack of metabolic adaptation during OF despite a wide variability in the response. Among the 30 subjects who returned for the 6-mo follow-up visit, those who had a lower-than-predicted SMR (basal EE) retained more of the fat gained during OF. Likewise, subjects displaying a higher-than-predicted sedentary 24h-EE lost significantly more fat during the 6-mo follow-up. CONCLUSIONS: Metabolic adaptation to OF was on average very small but variable between subjects, revealing "thrifty" or "spendthrift" metabolic phenotypes related to body weight loss 6 mo later. This trial was registered at clinicaltrials.gov as NCT01672632.

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Respiration chambers share one analyzer working in parallel, and methane (CH4) concentrations have to be measured at certain intervals. The maximum and minimum values in the kinetics of CH4 emissions can be missed during the interval between measurements, which may influence the quantification of CH4 emissions. Chambers must be opened for morning feeding and cleaning, which causes a loss of CH4 data. Calculation methods are needed to estimate the lost CH4 emission data, which may influence the estimated amount of daily CH4 emissions. In this study, we measured the CH4 emissions of 10 growing Chinese Holstein dairy heifers in respiration chambers. Methane concentrations were measured every 0.5 min to obtain the 23-h kinetics of CH4 emissions, which were further selected at different intervals between measurements (i.e., 5, 30, 60, 120, 180, and 240 min) to evaluate the effects of interval on quantification of CH4 emissions. The missing 1-h kinetics of CH4 emissions before feeding were not measured, and 2 calculation methods were used to estimate the missing 1-h kinetics of CH4 emissions: mean value of measuring period (the mean method) and the nearest value of measurement just before chamber opening (the nearest method). The results showed that the rates of CH4 emission from 10 heifers varied from 4.56 to 11.42 g/h. The increment of intervals decreased maximum rate of CH4 emission and increased minimum rate of CH4 emission. Interval caused less than 5% of the difference in measuring CH4 emissions. Although the mean method had greater estimated daily CH4 emission than the nearest method, the difference was within 3%. The interval between measurements (≤3 h) and calculation method had little influence on enteric CH4 emission measurements.

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We developed a novel method for computing diet-induced thermogenesis (DIT) in a respiratory chamber and evaluated the validity and reproducibility of the method. We hypothesized that DIT may be calculated as the difference between postprandial energy expenditure (EE) and estimated EE (sum of basal metabolic rate and physical activity (PA)-related EE). The estimated EE was derived from the regression equation between EE from respiration and PA intensity in the fasting state. It may be possible to evaluate the time course of DIT using this novel technique. In a validity study, we examined whether DIT became zero (theoretical value) for 6 h of fasting in 11 subjects. The mean value of DIT calculated by the novel and traditional methods was 22.4 ± 13.4 and 3.4 ± 31.8 kcal/6 h, respectively. In the reproducibility study, 15 adult subjects lived in the respiratory chamber for over 24 h on two occasions. The DIT over 15 h of postprandial wake time was calculated. There were no significant differences in the mean values of DIT between the two test days. The within-subject day-to-day coefficient of variation for calculated DIT with the novel and traditional methods was approximately 35% and 25%, respectively. The novel method did not have superior reproducibility compared with that of the traditional method. However when comparing the smaller variation in the fasting state than the theoretical value (zero), the novel method may be better for evaluating interindividual differences in DIT than the traditional method and also has the ability to evaluate the time-course.