Circadian rhythms in resting metabolic rate account for apparent daily rhythms in thermic effect of food

Context Daily variation in thermic effect of food (TEF) is commonly reported and proposed as a contributing factor to weight gain with late eating. However underlying circadian variability in resting metabolic rate (RMR) is an overlooked factor when calculating TEF associated with eating at different times of the day. Objective To determine whether methodological approaches to calculating TEF contribute to the reported phenomena of daily variation in TEF. Design, Setting and Participants: Fourteen overweight to obese but otherwise healthy subjects, had their resting and postprandial energy expenditure measured over 15.5 hours at a clinical research unit. TEF was calculated for breakfast, lunch and dinner using standard methods (above a baseline and premeal RMR measure) and compared to a method incorporating a circadian RMR where RMR was derived from a sinusoid curve model and TEF was calculated over and above the continuously changing RMR. Main Outcome measures TEF at breakfast, lunch and dinner calculated with different methods. Results Standard methods of calculating TEF above a premeal measured RMR showed that morning TEF [60.8kcal ± 5.6] (mean ± SEM) was 1.6 times greater than TEF at lunch [36.3kcal ± 8.4], and 2.4 times greater than dinner TEF [25.2kcal ± 9.6] (p=0.022). However, adjusting for modelled circadian RMR nullified any differences between breakfast [54.1kcal ± 30.8], lunch [49.5kcal ± 29.4], and dinner [49.1kcal ± 25.7] (p=0.680). Conclusions Differences in TEF between morning and evening can be explained by underlying circadian resting energy expenditure, which is independent of an acute effect of eating.

A randomized cross-over trial to determine the effect of a protein vs. carbohydrate preload on energy balance in ad libitum settings

Background Although high protein diets have been tested in controlled environments for applications to weight management, it is not understood if adding high protein foods to the diet would impact ad libitum energy balance in the absence of other lifestyle changes. Methods This double-blinded randomized crossover trial compared the effects of a protein shake (PS) to a carbohydrate shake (CS), consumed prior to each major meal to equate to 20% of total energy needs over the course of the day, on energy balance over two 5-day treatment periods in healthy adults with BMI 20–30 kg/m2. Tri-axial accelerometers estimated physical activity energy expenditure. Ad libitum energy intake was measured in a laboratory kitchen. Results Energy balance was positive during both treatment periods but was not different between periods. There were no interactions between treatment and preload caloric dose or treatment and BMI status on energy balance. Satiety ratings did not differ for any pairwise comparisons between treatment and caloric dose. Controlling for gender and basal metabolic rate, thermic effect of food was greater for PS than CS. Conclusions Preload periods significantly altered the macronutrient composition of the overall diet. This study found limited evidence that carbohydrate or protein preloads have differential effects on energy balance in short-term ad libitum settings. Trial registration This trial was pre-registered on clinicaltrials.gov as NCT02613065 on 11/30/2015.

An insulin-stimulated proteolytic mechanism links energy expenditure with glucose uptake

SummaryMechanisms to coordinately regulate energy expenditure and glucose uptake into muscle and fat cells are not well described. Insulin stimulates glucose uptake in part by causing site-specific endoproteolytic cleavage of TUG, which mobilizes GLUT4 glucose transporters to the cell surface. Here, we show that the TUG C-terminal cleavage product enters the nucleus, binds the transcriptional regulators PGC-1α and PPARγ, and increases oxidative metabolism and thermogenic protein expression. Muscle-specific genetic manipulation of this pathway impacts whole-body energy expenditure, independent of glucose uptake. The PPARγ2 Pro12Ala polymorphism, which reduces diabetes risk, enhances TUG binding. The TUG cleavage product stabilizes PGC-1α and is itself susceptible to an Ate1 arginyltransferase -dependent degradation mechanism; binding of the TUG product confers Ate1-dependent stability upon PGC-1α. We conclude that TUG cleavage coordinates energy expenditure with glucose uptake, that this pathway may contribute to the thermic effect of food, and that its attenuation may be important in obesity.

Effects of Altering Levothyroxine Dose on Energy Expenditure and Body Composition in Subjects Treated With LT4

Background It is unclear whether variations in thyroid status within or near the reference range affect energy expenditure, body mass, or body composition. Methods 138 subjects treated with levothyroxine (LT4) for hypothyroidism with normal TSH levels underwent measurement of total, resting, and physical activity energy expenditure; thermic effect of food; substrate oxidation; dietary intake; and body composition. They were assigned to receive an unchanged, higher, or lower LT4 dose in randomized, double-blind fashion, targeting one of three TSH ranges (0.34 to 2.50, 2.51 to 5.60, or 5.61 to 12.0 mU/L). The doses were adjusted every 6 weeks to achieve target TSH levels. Baseline measures were reassessed at 6 months. Results At study end, the mean LT4 doses and TSH levels were 1.50 ± 0.07, 1.32 ± 0.07, and 0.78 ± 0.08 µg/kg (P < 0.001) and 1.85 ± 0.25, 3.93 ± 0.38, and 9.49 ± 0.80 mU/L (P < 0.001), respectively, in the three arms. No substantial metabolic differences in outcome were found among the three arms, although direct correlations were observed between decreases in thyroid status and decreases in resting energy expenditure for all subjects. The subjects could not ascertain how their LT4 dose had been adjusted but the preferred LT4 dose they perceived to be higher (P < 0.001). Conclusions Altering LT4 doses in subjects with hypothyroidism to vary TSH levels in and near the reference range did not have major effects on energy expenditure or body composition. Subjects treated with LT4 preferred the perceived higher LT4 doses despite a lack of objective effect. Our data do not support adjusting LT4 doses in patients with hypothyroidism to achieve potential improvements in weight or body composition.

Abstract P125: Aerobic Exercise Training Reduces Postprandial Thermogenesis in Older Women

Introduction: Thermic effect of food is a component of total daily energy expenditure (TDEE). Some literature suggests lower postprandial rise in energy expenditure predicts future weight gain. It is also known that other components of TDEE, resting metabolic rate (RMR) and free-living physical activity energy expenditure, are prone to change in response to exercise training. However, most studies estimate thermic effect of food as a proportion of TDEE and thus have not evaluated whether changes in postprandial thermogenesis occur in response to exercise training. The objective of this study was to determine whether postprandial thermogenesis changed after completing aerobic exercise training in older women. Hypothesis: We hypothesize that the postprandial thermogenesis decreases in sedentary older women who complete 16-week aerobic exercise training. Methods: Sedentary older women (n = 47; age = 65.1 ± 4.3 years) completed 16-week moderate-intensity aerobic exercise training. RMR and 5-hour postprandial thermogenesis following ingesting the same meal, before and at the end of training, was measured via indirect calorimetry. The meal consisted of approximately 40% of each woman’s RMR at baseline. Postprandial thermogenesis was calculated as area under the curve. TDEE was also measured using doubly labelled water before and at the end of training. Results: After exercise training, RMR and TDEE did not change (p > 0.05 for both). Total postprandial thermogenesis (from 287 ±36 to 276 ± 40 kcal for 5 hours, p = 0.008) and postprandial thermogenesis in the first hour (from 69.9±8.7 to 66.3±8.1 kcal, p = 0.05) decreased significantly. The ratios of total and first-hour postprandial thermogenesis to TDEE also decreased (p = 0.026 and 0.013, respectively). Conclusion: Postprandial thermogenesis following the same meal reduced after aerobic training in older women. This adaptive change may contribute to an individual’s ability to defend the body’s energy store.