Maintenance of a reduced body weight is accompanied by a decrease in energy expenditure beyond that accounted for by reduced body mass and composition, as well as by an increased drive to eat. These effects appear to be due— in part—to reductions in circulating leptin concentrations due to loss of body fat. Gut microbiota have been implicated in the regulation of body weight. The effects of weight loss on qualitative aspects of gut microbiota have been studied in humans and mice, but these studies have been confounded by concurrent changes in diet composition, which influence microbial community composition. We studied the impact of 20% weight loss on the microbiota of diet-induced obese (DIO: 60% calories fat) mice on a high-fat diet (HFD). Weight-reduced DIO (DIO-WR) mice had the same body weight and composition as control (CON) adlibitum (AL) fed mice being fed a control diet (10% calories fat), allowing a direct comparison of diet and weight-perturbation effects. Microbial community composition was assessed by pyrosequencing 16S rRNA genes derived from the ceca of sacrificed animals. There was a strong effect of diet composition on the diversity and composition of the microbiota. The relative abundance of specific members of the microbiota was correlated with circulating leptin concentrations and gene expression levels of inflammation markers in subcutaneous white adipose tissue in all mice. Together, these results suggest that both host adiposity and diet composition impact microbiota composition, possibly through leptin-mediated regulation of mucus production and/or inflammatory processes that alter the gut habitat.

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Mammals regulate fat mass, so that increases or reductions in adipose tissue mass activate responses that favor return to one’s previous weight: A reduction in fat mass activates a system that increases food intake and reduces energy expenditure, and conversely, overfeeding and rapid adipose tissue expansion reduces food intake and increases energy expenditure. With the identification of leptin nearly two decades ago the central circuit that defends against reductions in body fat was revealed. However, the systems that defend against rapid expansion of fat mass remain largely unknown. Here we review the physiology of the overfed state and evidence for a distinct regulatory system, which unlike the leptin-mediated system, we propose primarily measures a functional aspect of adipose tissue and not total mass per se.

Homeotherms have specific mechanisms to maintain a constant core body temperature despite changes in thermal environment, food supply, and metabolic demand. Brown adipose tissue, the principal thermogenic organ, quickly and efficiently increases heat production by dissipating the mitochondrial proton motive force. It has been suggested that activation of brown fat, via either environmental (i.e. cold exposure) or pharmacologic means, could be used to increase metabolic rate and thus reduce body weight. Here we assess the effects of intermittent cold exposure (4°C for one to eight hours three times a week) on C57BL/6J mice fed a high fat diet. Cold exposure increased metabolic rate approximately two-fold during the challenge and activated brown fat. In response, food intake increased to compensate fully for the increased energy expenditure; thus, the mice showed no reduction in body weight or adiposity. Despite the unchanged adiposity, the cold-treated mice showed transient improvements in glucose homeostasis. Administration of the cannabinoid receptor-1 inverse agonist AM251 caused weight loss and improvements in glucose homeostasis, but showed no further improvements when combined with cold exposure. These data suggest that intermittent cold exposure causes transient, meaningful improvements in glucose homeostasis, but without synergy when combined with AM251. Since energy expenditure is significantly increased during cold exposure, a drug that dissociates food intake from metabolic demand during cold exposure may achieve weight loss and further metabolic improvements.

We investigated the role of leptin in regulating energy metabolism through induction of uncoupling protein (UCP)-1-based brown fat thermogenesis by comparing phenotypes of energy balance in ob/ob and double-mutant ob/ob.Ucp1(-/-) mice. Measurements of adiposity and lean body mass (nuclear magnetic resonance), energy expenditure (indirect calorimetry), body weight, food intake, and core body temperature were determined in the two mutant stocks of 3-month-old mice maintained at an initial ambient temperature of 28 C for 21 d and then at 21 C for 16 d, and finally with leptin administration for 8 d at 21 C. No phenotypic differences between ob/ob and ob/ob.Ucp1(-/-) mice were detected, suggesting that UCP1-based thermogenesis is not essential for the regulation of adiposity in ob/ob mice at temperatures between 21 and 28 C. Although both Ucp1(-/-) and ob/ob mice can survive in extreme cold at 4 C, provided they are adapted to the cold by gradually lowering ambient temperature, ob/ob.Ucp1(-/-) mice could not adapt and survive at temperatures lower than 12 C unless they were administered leptin. As the ambient temperature was reduced from 20 to 16 C, ob/ob.Ucp1(-/-) mice treated with leptin have elevated levels of circulating T(3) that correlate with elevated sarcoendoplasmic reticulum Ca(2+) ATPase 2a mRNA levels in gastrocnemius muscle. Furthermore, ob/ob.Ucp1(-/-) mice, treated with T(3), were able to maintain body temperature and stimulate sarcoendoplasmic reticulum Ca(2+) ATPase 2a expression when the ambient temperature was gradually reduced to 4 C. Thus, in the absence of UCP1, leptin-induced thermogenesis protects body temperature in part through its action on the thyroid hormone axis.

Objective To compare, in mice, the accuracy of estimates of energy expenditure using an energy balance technique (TEEbal : food energy intake and body composition change) versus indirect calorimetry (TEEIC). Subjects In 32 male C57BL/6J mice energy expenditure was estimated using an energy balance (caloric intake minus change in body energy stores) method over a 37 day period. Energy expenditure was also measured in the same animals by indirect calorimetry. These measures were compared. Results The two methods were highly correlated (r2 = 0.87: TEEbal = 1.07 * TEEIC − 0.22, p < 0.0001). By Bland-Altman analysis, TEEbal estimates were slightly higher (4.6±1.5%; p < 0.05) than TEEIC estimates (Bias = 0.55 kcal/24h). Conclusion TEEbal can be performed in “home cages” and provides an accurate integrated long-term measurement of energy expenditure while minimizing potentially confounding stress that may accompany the use of indirect calorimetry systems. The technique can also be used to assess long term energy intake.

Leibel RL. Effects of chronic weight perturbation on energy homeostasis and brain structure in mice. Am J Physiol Regul Integr Comp Physiol 300: R1352-R1362, 2011. First published March 16, 2011 doi:10.1152/ajpregu.00429.2010.-Maintenance of reduced body weight in lean and obese human subjects results in the persistent decrease in energy expenditure below what can be accounted for by changes in body mass and composition. Genetic and developmental factors may determine a central nervous system (CNS)-mediated minimum threshold of somatic energy stores below which behavioral and metabolic compensations for weight loss are invoked. A critical question is whether this threshold can be altered by environmental influences and by what mechanisms such alterations might be achieved. We examined the bioenergetic, behavioral, and CNS structural responses to weight reduction of diet-induced obese (DIO) and never-obese (CON) C57BL/6J male mice. We found that weightreduced (WR) DIO-WR and CON-WR animals showed reductions in energy expenditure, adjusted for body mass and composition, comparable (Ϫ10 -15%) to those seen in human subjects. The proportion of excitatory synapses on arcuate nucleus proopiomelanocortin neurons was decreased by ϳ50% in both DIO-WR and CON-WR mice. These data suggest that prolonged maintenance of an elevated body weight (fat) alters energy homeostatic systems to defend a higher level of body fat. The synaptic changes could provide a neural substrate for the disproportionate decline in energy expenditure in weight-reduced individuals. This response to chronic weight elevation may also occur in humans. The mouse model described here could help to identify the molecular/cellular mechanisms underlying both the defense mechanisms against sustained weight loss and the upward resetting of those mechanisms following sustained weight gain. obesity; set point; energy metabolism; POMC neurons LONG-TERM MAINTENANCE OF EVEN modest reductions in body weight ameliorates or eliminates many of the comorbidities of obesity (10). The recidivism rate to obesity in formerly obese individuals is 75-85% (59), reflecting the potent metabolic and environmental pressures opposing long-term maintenance of a reduced body weight. We have previously shown that the maintenance of a 10% or greater reduction in body weight in both lean and obese humans is associated with a decrease in energy expenditure (EE) that is 15-20% below what can be accounted for by changes in body mass and body composition.This adaptive thermogenesis does not abate over time (46) and predominantly reflects increased mechanical work efficiency of skeletal muscle, decreased circulating concentrations of bioactive thyroid hormones, and reduced sympathetic autonomic nervous system tone (2,32,46,54).Leptin is an adipocyte-derived hormone whose circulating plasma concentrations are correlated with fat stores at usual (stable) body weight but which rapidly decline during food restriction and/or fasting (1, 52). We have proposed that central nervous system (CNS) en...