Central neural and endocrine mechanisms of non-exercise activity thermogenesis and their potential impact on obesity

Associations between sleep duration, sleep quality, and weight status in Chinese children and adolescents

Background and objective

The high prevalence of obesity is a serious problem, and sleep is considered to be a factor for obesity. This study aimed to examine the relationship between sleep duration, sleep quality, and weight status among children and adolescents in China and to explore whether the relationship between sleep duration and weight status is independent of sleep quality. Sex and age differences were also explored.

Methods

A cross-sectional research was conducted among 2019 children and adolescents (1029 boys and 990 girls) aged 8–16 years in Shanghai. An open-question was used to obtain data on sleep duration, which was categorized into the following four groups based on the age-specific National Sleep Foundation Sleep Duration Recommendations: 1) very short, 2) short, 3) recommended, and 4) long. The Pittsburgh Sleep Quality Index was used to assess sleep quality. Weight and height were measured for all participants. The variable weight status was estimated with the Chinese children and adolescent age- and sex-specific body mass index (BMI) and was categorized into overweight/obesity and normal weight.

Results

Short sleep duration (7–8 and 6–7 h for 6–13 and 14–16 years old, respectively) significantly increased odds of overweight/obesity (OR = 1.32, 95% CI: 1.06–1.64) compared with that of the recommended sleep duration (9–11 and 8–10 h for 6–13 and 14–16 years old, respectively). The relationship between the two variables existed independent of sleep quality. No significant relationship was found between sleep quality and overweight/obesity of children and adolescents. Sleep quality (OR = 1.07, 95% CI: 1.01–1.14) and short sleep duration (OR = 1.51, 95% CI: 1.06–2.13) increased the risk for overweight/obesity among girls, whereas no significant relationships between sleep duration, sleep quality, and overweight/obesity were found among boys. Short sleep duration increased the risk of overweight/obesity in children aged 8–13 years (OR = 1.34, 95% CI: 1.05–1.71), independent of sleep quality, but no significant relationships between these two variables existed for adolescents aged 14–16 years.

Conclusions

Overall, short sleep duration increased the risks of overweight/obesity in children and adolescents in China, independent of sleep quality. This relationship is significant for girls and children aged 8–13 years instead of boys and adolescents aged 14–16 years. Interventions to extend the sleep duration of children and adolescents, especially girls and children aged 8–13 years in China, are necessary to improve their weight status.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-13534-w.

Chronic Red Bull Consumption during Adolescence: Effect on Mesocortical and Mesolimbic Dopamine Transmission and Cardiovascular System in Adult Rats

Energy drinks are very popular nonalcoholic beverages among adolescents and young adults for their stimulant effects. Our study aimed to investigate the effect of repeated intraoral Red Bull (RB) infusion on dopamine transmission in the nucleus accumbens shell and core and in the medial prefrontal cortex and on cardiac contractility in adult rats exposed to chronic RB consumption. Rats were subjected to 4 weeks of RB voluntary consumption from adolescence to adulthood. Monitoring of in vivo dopamine was carried out by brain microdialysis. In vitro cardiac contractility was studied on biomechanical properties of isolated left-ventricular papillary muscle. The main finding of the study was that, in treated animals, RB increased shell dopamine via a nonadaptive mechanism, a pattern similar to that of drugs of abuse. No changes in isometric and isotonic mechanical parameters were associated with chronic RB consumption. However, a prolonged time to peak tension and half-time of relaxation and a slower peak rate of tension fall were observed in RB-treated rats. It is likely that RB treatment affects left-ventricular papillary muscle contraction. The neurochemical results here obtained can explain the addictive properties of RB, while the cardiovascular investigation findings suggest a hidden papillary contractility impairment.

Aerobic capacity modulates adaptive thermogenesis: Contribution of non-resting energy expenditure

Decreases in energy stores requires negative energy balance where caloric expenditure exceeds energy intake, which can induce adaptive thermogenesis-the reduction of energy expenditure (EE) beyond that accounted for by the weight lost. Adaptive thermogenesis varies between individuals. The component of total daily EE responsible for the interindividual variation in adaptive thermogenesis was investigated in this study, using a rat model that differs in obesity propensity and physical activity. Total daily EE and physical activity were examined before and after 21 days of 50% calorie restriction in male and female rats with lean and obesity-prone phenotypes-rats selectively bred for high and low intrinsic aerobic capacity (HCR and LCR, respectively). Calorie restriction significantly decreased EE more than was predicted by loss of weight and lean mass, demonstrating adaptive thermogenesis. Within sex, HCR and LCR did not significantly differ in resting EE. However, the calorie restriction-induced suppression in non-resting EE, which includes activity EE, was significantly greater in HCR than in LCR; this phenotypic difference was significant for both male and female rats. Calorie restriction also significantly suppressed physical activity levels more in HCR than LCR. When VO2max was assessed in male rats, calorie restriction significantly decreased O2 consumption without significantly affecting running performance (running time, distance), indicating increased energy efficiency. Percent weight loss did not significantly differ between groups. Altogether, these results suggest that individual differences in calorie restriction-induced adaptive thermogenesis may be accounted for by variation in aerobic capacity. Moreover, it is likely that activity EE, not resting or basal metabolism, may explain or predict the variation in individuals' adaptive thermogenesis.

Nonexercise Activity Thermogenesis-Induced Energy Shortage Improves Postprandial Lipemia and Fat Oxidation

(1) Background: This study investigated the effect of nonexercise activity thermogenesis on postprandial triglyceride (TG) concentrations; (2) Methods: Ten healthy males completed a sedentary trial (ST) and a physical activity trial (PA) in a random order separated by at least 7 days. After each intervention on day 1, the participants consumed a high-fat test meal on the next day. The blood samples and gas sample were observed in the fasted state and for 4 h after consuming the oral fat tolerance test; (3) Results: The postprandial TG concentrations of total (AUC) (p = 0.008) and incremental area under the curve (IAUC) (p = 0.023) in the plasma of participants in the PA trial were significantly lower than those in the plasma of participants in the ST trial. The postprandial fat oxidation rate AUC of the PA trial was significantly higher than that of the ST trial (p = 0.009); (4) Conclusions: The results of this study indicated that nonexercise energy expenditure decrease the postprandial TG concentration and increase the fat oxidation the next day.

Memory-Related Encoding-Specificity Paradigm: Experimental Application to the Exercise Domain

The Encoding-Specificity Paradigm indicates that memory recall will be superior when contextual factors are congruent between memory encoding and memory retrieval. However, unlike other contextual conditions (e.g., verbal context, mental operations, global feature context, mood dependency, and physical operations), this paradigm has nearly been ignored in the exercise domain. Thus, the purpose of this study was to examine the Encoding-Specificity Paradigm in the context of exercise and rest conditions. 24 young adults (age: M = 21 years) completed a within-subject, counterbalanced experiment involving four laboratory visits, including 1) R-R (rest-rest) condition, 2) R-E (rest-exercise) condition, 3) E-R (exercise-rest) condition, or 4) E-E (exercise-exercise) condition. The exercise bout included a 15-minute moderate-intensity walk on a treadmill. Memory recall was assessed via a 15 word-list task. Memory recall was greater for R-R (8.71 ± 3.1) versus R-E (7.46 ± 2.8), and similarly, for E-E (8.63 ± 2.7) versus E-R (8.21 ± 2.7). The mean word recall for the congruent and incongruent conditions, respectively, was 8.67 (2.4) and 7.83 (2.4). There was a statistically significant condition effect (F = 5.02; P = .03; partial η² = .18). This experiment provides direct support for the Encoding-Specificity Paradigm in the exercise domain.

Caffeine enhances activity thermogenesis and energy expenditure in rats

Caffeine and its derivatives have been used, alone and in combination with other phytochemicals, as weight-loss supplements. Caffeine affects several physiological and behavioural aspects of energy balance, including increasing locomotor activity. This study investigates the potential for caffeine to enhance activity thermogenesis and energy expenditure (EE) even when activity level is held constant. To do this, EE and muscle thermogenesis were measured in rats during treadmill walking regimens, with and without caffeine (25 mg/kg, ip). Activity-related EE was significantly increased throughout the treadmill walking protocol. Muscle heat dissipation, on the other hand, was significantly increased by caffeine only at the end of the 25-minute treadmill test. This study demonstrates that caffeine increases the caloric cost of physical activity, compared to the caloric cost of that same physical activity without caffeine, implicating decreased muscle work efficiency. Combined with the known ability of caffeine to increase locomotor activity, the decreased locomotor efficiency imparted by caffeine may further augment the potential for caffeine to enhance caloric expenditure.

Continuous versus intermittent moderate energy restriction for increased fat mass loss and fat free mass retention in adult athletes: protocol for a randomised controlled trial-the ICECAP trial (Intermittent versus Continuous Energy restriction Compared in an Athlete Population)

Introduction

Reducing fat mass (FM) while retaining fat free mass (FFM) is a common goal of athletes. Evidence suggests that some-but not all-forms of intermittent energy restriction (IER) may be superior to the conventional method of continuous energy restriction (CER) for people with excess body fat that are sedentary, by reducing some of the adaptive responses to ER. However, it is yet to be established whether this dietary approach is effective for athletes.

Methods and analysis

A single-blind, parallel group, randomised controlled trial with a 1:1 allocation ratio is proposed. Sixty healthy athletes aged ≥18 years will be recruited from local sporting facilities and randomised to an intervention of either moderate CER (mCER) or moderate IER (mIER). Both interventions will consist of 12 weeks of moderate ER, plus 3 weeks in energy balance (EB). The mCER intervention will entail 12 weeks of continuous moderate ER, followed by 3 weeks in EB. The mIER intervention will entail 12 weeks of moderate ER, administered as 4×3 week blocks of moderate ER, interspersed with 3×1 week blocks of EB. The co-primary outcomes are changes in FM and FFM after 12 weeks of moderate ER. Secondary outcomes will be changes in FM and FFM at 15 weeks after intervention commencement, as well as muscle performance, physical activity, sleep quality, changes in resting energy expenditure, subjective drive to eat, circulating concentrations of appetite-regulating hormones, mood states and diet acceptability.

Trial registration

ACTRN12618000638235p.

Central and peripheral effects of physical exercise without weight reduction in obese and lean mice

To investigate the central (hypothalamic) and peripheral effects of exercise without body weight change in diet-induced obesity (DIO). Twelve-week-old male C57Bl/6 mice received a control (C) or a high-fat diet (H). Half of them had free access to running wheels for 5 days/week for 10 weeks (CE) and HE, respectively). Hypothalamic expression of genes related to energy homeostasis, and leptin (Stat3 and p-Stat3) and insulin (Akt and p-Akt) signaling were evaluated. Glucose and leptin tolerance, peripheral insulin sensitivity, and plasma insulin, leptin and adiponectin were determined. Perigonadal and retroperitoneal fat depots were increased by diet but reduced by exercise despite lack of effect of exercise on body weight. Blood glucose during intraperitoneal glucose tolerance test (ipGTT) was higher and glucose decay during intraperitoneal insulin tolerance test (ipITT) was lower in H and HE compared with C and CE. Exercise increased liver p-Akt expression and reduced fast glycemia. High-fat diet increased plasma insulin and leptin. Exercise had no effect on insulin but decreased leptin and increased adiponectin. Leptin inhibited food intake in all groups. Hypothalamic total and p-Stat3 and Akt were similar amongst the groups despite higher plasma levels of leptin and insulin in H and HE mice. High-fat diet modulated gene expression favoring a positive energy balance. Exercise only marginally changed the gene expression. Exercise induced positive changes (decreased fast glycemia and fat depots; increased liver insulin signaling and adiponectin concentration) without weight loss. Thus, despite reducing body weight could bring additional benefits, the effects of exercise must not be overlooked when weight reduction is not achieved.

Spontaneous physical activity and mediators of energy homeostasis in the hypothalamus of mice from 4 to 10 months of age

NEW FINDINGS

What is the central question of this study? Is the initial decline of spontaneous physical activity (SPA) in mice related to impaired insulin and leptin signalling or brain-derived neurotrophic factor expression in the hypothalamus? What is the main finding and its importance? We showed that SPA started to decline at an early stage, concomitantly with an impairment of hypothalamic leptin signalling. Consequently, energy expenditure decreased and glucose tolerance worsened. Our results demonstrate the need to counteract the initial decline in SPA to avoid metabolic impairments and indicate the possible involvement of central leptin in the reduction in SPA with age. The biological control of physical activity is poorly understood. Age decreases insulin, leptin and brain-derived neurotrophic factor (BDNF) signalling in the hypothalamus, and all have been shown to modulate spontaneous physical activity (SPA). We investigated the age at which SPA starts to decline and whether this is associated with the emergence of hypothalamic insulin and leptin resistance and reduced BDNF expression. Spontaneous physical activity (and other parameters of locomotion) and energy expenditure were determined monthly in mice from the 4th to the 10th month of age. Metabolic and hypothalamic analyses were performed in 4-, 6- and 10-month-old mice. Spontaneous physical activity, distance travelled and speed of locomotion started to decrease in 6-month-old mice. The reduction in SPA became more evident from 8 months of age. Energy expenditure decreased from the 8th month. Hypothalamic BDNF protein expression and insulin signalling did not change throughout the time span studied. Leptin signalling decreased at 6 and 10 months compared with 4 months. Also, compared with 4 months, 6- and 10-month-old mice were glucose intolerant. In conclusion, SPA begins to decline in parallel with reduced hypothalamic leptin signalling. Metabolic impairment also manifests as SPA decreases, highlighting the need to understand the regulation of SPA in order to combat its decline.

Effect of frequent interruptions of prolonged sitting on self-perceived levels of energy, mood, food cravings and cognitive function

Background

While physical activity has been shown to improve cognitive performance and well-being, office workers are essentially sedentary. We compared the effects of physical activity performed as (i) one bout in the morning or (ii) as microbouts spread out across the day to (iii) a day spent sitting, on mood and energy levels and cognitive function.

Methods

In a randomized crossover trial, 30 sedentary adults completed each of three conditions: 6 h of uninterrupted sitting (SIT), SIT plus 30 min of moderate-intensity treadmill walking in the morning (ONE), and SIT plus six hourly 5-min microbouts of moderate-intensity treadmill walking (MICRO). Self-perceived energy, mood, and appetite were assessed with visual analog scales. Vigor and fatigue were assessed with the Profile of Mood State questionnaire. Cognitive function was measured using a flanker task and the Comprehensive Trail Making Test. Intervention effects were tested using linear mixed models.

Results

Both ONE and MICRO increased self-perceived energy and vigor compared to SIT (p < 0.05 for all). MICRO, but not ONE, improved mood, decreased levels of fatigue and reduced food cravings at the end of the day compared to SIT (p < 0.05 for all). Cognitive function was not significantly affected by condition.

Conclusions

In addition to the beneficial impact of physical activity on levels of energy and vigor, spreading out physical activity throughout the day improved mood, decreased feelings of fatigue and affected appetite. Introducing short bouts of activity during the workday of sedentary office workers is a promising approach to improve overall well-being at work without negatively impacting cognitive performance.

Trial registration

NCT02717377, registered 22 March 2016.

Voluntary running decreases nonexercise activity in lean and diet-induced obese mice

PURPOSE

Determine whether voluntary wheel running triggers compensatory changes in nonexercise activity in lean and high-fat diet fed mice.

METHODS

C57Bl/6 mice received a control (C) or a high-fat diet (H) and half of them had free access to a running wheel 5days/week (CE and HE, respectively) for 10weeks. Energy intake, nonexercise activity (global activity, distance covered and average speed of displacement in the home cage) and energy expenditure (EE) were evaluated at weeks 5 and 10 during the 2days without the wheels.

RESULTS

High-fat diet increased weight gain in H (110%) and HE (60%) groups compared to C and CE groups, respectively, with no effect of exercise. Wheel running increased energy intake (26% CE, 11% HE in week 5; 7% CE, 45% HE in week 10) and decreased distance covered (26% for both CE and HE in week 5; 35% CE and 13% HE in week 10) and average speed (35% CE and 13% HE in week 5; 45% CE and 18% HE in week 10) compared to the respective nonexercised groups. In week 10 there was an interaction between diet and exercise for global activity, which was reduced nearly 18% in CE, H, and HE groups compared to C. Access to a running wheel increased EE in week 5 (11% CE and 16% HE) but not in week 10, which is consistent with the period of highest running (number of turns: weeks 1-5 nearly 100%>weeks 6-10 for CE and HE groups). EE was reduced in H (19%) and HE (12%) groups compared to C and CE, in week 10.

CONCLUSION

Voluntary running causes a compensatory decrease in nonexercise activity and an increase in energy intake, both contributing to the lack of effect of exercise on body mass.

Voluntary Running Aids to Maintain High Body Temperature in Rats Bred for High Aerobic Capacity

The production of heat, i.e., thermogenesis, is a significant component of the metabolic rate, which in turn affects weight gain and health. Thermogenesis is linked to physical activity (PA) level. However, it is not known whether intrinsic exercise capacity, aging, and long-term voluntary running affect core body temperature. Here we use rat models selectively bred to differ in maximal treadmill endurance running capacity (Low capacity runners, LCR and High capacity Runners, HCR), that as adults are divergent for aerobic exercise capacity, aging, and metabolic disease risk to study the connection between PA and body temperature. Ten high capacity runner (HCR) and ten low capacity runner (LCR) female rats were studied between 9 and 21 months of age. Rectal body temperature of HCR and LCR rats was measured before and after 1-year voluntary running/control intervention to explore the effects of aging and PA. Also, we determined whether injected glucose and spontaneous activity affect the body temperature differently between LCR and HCR rats at 9 vs. 21 months of age. HCRs had on average 1.3°C higher body temperature than LCRs (p < 0.001). Aging decreased the body temperature level of HCRs to similar levels with LCRs. The opportunity to run voluntarily had a significant impact on the body temperature of HCRs (p < 0.001) allowing them to maintain body temperature at a similar level as when at younger age. Compared to LCRs, HCRs were spontaneously more active, had higher relative gastrocnemius muscle mass and higher UCP2, PGC-1α, cyt c, and OXPHOS levels in the skeletal muscle (p < 0.050). These results suggest that higher PA level together with greater relative muscle mass and higher mitochondrial content/function contribute to the accumulation of heat in the HCRs. Interestingly, neither aging nor voluntary training had a significant impact on core body temperature of LCRs. However, glucose injection resulted in a lowering of the body temperature of LCRs (p < 0.050), but not that of HCRs. In conclusion, rats born with high intrinsic capacity for aerobic exercise and better health have higher body temperature compared to rats born with low exercise capacity and disease risk. Voluntary running allowed HCRs to maintain high body temperature during aging, which suggests that high PA level was crucial in maintaining the high body temperature of HCRs.

Metabolic signals in sleep regulation: recent insights

Sleep and energy balance are essential for health. The two processes act in concert to regulate central and peripheral homeostasis. During sleep, energy is conserved due to suspended activity, movement, and sensory responses, and is redirected to restore and replenish proteins and their assemblies into cellular structures. During wakefulness, various energy-demanding activities lead to hunger. Thus, hunger promotes arousal, and subsequent feeding, followed by satiety that promotes sleep via changes in neuroendocrine or neuropeptide signals. These signals overlap with circuits of sleep-wakefulness, feeding, and energy expenditure. Here, we will briefly review the literature that describes the interplay between the circadian system, sleep-wake, and feeding-fasting cycles that are needed to maintain energy balance and a healthy metabolic profile. In doing so, we describe the neuroendocrine, hormonal/peptide signals that integrate sleep and feeding behavior with energy metabolism.

Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials

Energy restriction induces physiological effects that hinder further weight loss. Thus, deliberate periods of energy balance during weight loss interventions may attenuate these adaptive responses to energy restriction and thereby increase the efficiency of weight loss (i.e. the amount of weight or fat lost per unit of energy deficit). To address this possibility, we systematically searched MEDLINE, PreMEDLINE, PubMed and Cinahl and reviewed adaptive responses to energy restriction in 40 publications involving humans of any age or body mass index that had undergone a diet involving intermittent energy restriction, 12 with direct comparison to continuous energy restriction. Included publications needed to measure one or more of body weight, body mass index, or body composition before and at the end of energy restriction. 31 of the 40 publications involved 'intermittent fasting' of 1-7-day periods of severe energy restriction. While intermittent fasting appears to produce similar effects to continuous energy restriction to reduce body weight, fat mass, fat-free mass and improve glucose homeostasis, and may reduce appetite, it does not appear to attenuate other adaptive responses to energy restriction or improve weight loss efficiency, albeit most of the reviewed publications were not powered to assess these outcomes. Intermittent fasting thus represents a valid--albeit apparently not superior--option to continuous energy restriction for weight loss.

Contribution of regional brain melanocortin receptor subtypes to elevated activity energy expenditure in lean, active rats

Physical activity and non-exercise activity thermogenesis (NEAT) are crucial factors accounting for individual differences in body weight, interacting with genetic predisposition. In the brain, a number of neuroendocrine intermediates regulate food intake and energy expenditure (EE); this includes the brain melanocortin (MC) system, consisting of MC peptides as well as their receptors (MCR). MC3R and MC4R have emerged as critical modulators of EE and food intake. To determine how variance in MC signaling may underlie individual differences in physical activity levels, we examined behavioral response to MC receptor agonists and antagonists in rats that show high and low levels of physical activity and NEAT, that is, high- and low-capacity runners (HCR, LCR), developed by artificial selection for differential intrinsic aerobic running capacity. Focusing on the hypothalamus, we identified brain region-specific elevations in expression of MCR 3, 4, and also MC5R, in the highly active, lean HCR relative to the less active and obesity-prone LCR. Further, the differences in activity and associated EE as a result of MCR activation or suppression using specific agonists and antagonists were similarly region-specific and directly corresponded to the differential MCR expression patterns. The agonists and antagonists investigated here did not significantly impact food intake at the doses used, suggesting that the differential pattern of receptor expression may by more meaningful to physical activity than to other aspects of energy balance regulation. Thus, MCR-mediated physical activity may be a key neural mechanism in distinguishing the lean phenotype and a target for enhancing physical activity and NEAT.

Nonexercise activity thermogenesis in obesity management

Obesity is linked to cardiovascular disease. The global increase in sedentary lifestyle is an important factor contributing to the rising prevalence of the obesity epidemic. Traditionally, counseling has focused on moderate- to vigorous-intensity exercise, with disappointing results. Nonexercise activity thermogenesis (NEAT) is an important component of daily energy expenditure. It represents the common daily activities, such as fidgeting, walking, and standing. These high-effect NEAT movements could result in up to an extra 2000 kcal of expenditure per day beyond the basal metabolic rate, depending on body weight and level of activity. Implementing NEAT during leisure-time and occupational activities could be essential to maintaining a negative energy balance. NEAT can be applied by being upright, ambulating, and redesigning workplace and leisure-time environments to promote NEAT. The benefits of NEAT include not only the extra calories expended but also the reduced occurrence of the metabolic syndrome, cardiovascular events, and all-cause mortality. We believe that to overcome the obesity epidemic and its adverse cardiovascular consequences, NEAT should be part of the current medical recommendations. The content of this review is based on a literature search of PubMed and the Google search engine between January 1, 1960, and October 1, 2014, using the search terms physical activity, obesity, energy expenditure, nonexercise activity thermogenesis, and NEAT.

Sleep disorders, obesity, and aging: the role of orexin

The hypothalamic neuropeptides orexin A and B (hypocretin 1 and 2) are important homeostatic mediators of central control of energy metabolism and maintenance of sleep/wake states. Dysregulation or loss of orexin signaling has been linked to narcolepsy, obesity, and age-related disorders. In this review, we present an overview of our current understanding of orexin function, focusing on sleep disorders, energy balance, and aging, in both rodents and humans. We first discuss animal models used in studies of obesity and sleep, including loss of function using transgenic or viral-mediated approaches, gain of function models using exogenous delivery of orexin receptor agonist, and naturally-occurring models in which orexin responsiveness varies by individual. We next explore rodent models of orexin in aging, presenting evidence that orexin loss contributes to age-related changes in sleep and energy balance. In the next section, we focus on clinical importance of orexin in human obesity, sleep, and aging. We include discussion of orexin loss in narcolepsy and potential importance of orexin in insomnia, correlations between animal and human studies of age-related decline, and evidence for orexin involvement in age-related changes in cognitive performance. Finally, we present a summary of recent studies of orexin in neurodegenerative disease. We conclude that orexin acts as an integrative homeostatic signal influencing numerous brain regions, and that this pivotal role results in potential dysregulation of multiple physiological processes when orexin signaling is disrupted or lost.

Physically active rats lose more weight during calorie restriction

Daily physical activity shows substantial inter-individual variation, and low physical activity is associated with obesity and weight gain. Elevated physical activity is also associated with high intrinsic aerobic capacity, which confers considerable metabolic health benefits. Rats artificially selected for high intrinsic aerobic capacity (high-capacity runners, HCR) are more physically active than their low-capacity counterparts (low-capacity runners, LCR). To test the hypothesis that physical activity counters metabolic thriftiness, we measured physical activity and weight loss during three weeks of 50% calorie restriction (CR) in the HCR and LCR rat lines. At baseline, HCR ate more and were more active than LCR; this was seen in male rats, where LCR are considerably heavier than HCR, as well as in a set of female rats where body weight did not differ between the lines, demonstrating that this effect is consistent across sex and not secondary to body weight. We show for the first time that HCR lose more weight than LCR relative to baseline. Physical activity levels declined throughout CR, and this was more pronounced in HCR than in LCR, yet some aspects of activity remained elevated in HCR relative to LCR even during CR. This is consistent with the idea that low physical activity contributes to metabolic thriftiness during food restriction, allowing LCR to defend body mass, particularly lean mass. This has implications for physical activity during diet-induced weight loss, the genetic underpinnings of individual differences in weight loss during a diet, and the potential evolutionary opposition between metabolic thriftiness and aerobic capacity.

Using sit-stand workstations to decrease sedentary time in office workers: a randomized crossover trial

Objective: This study was conducted to determine whether installation of sit-stand desks (SSDs) could lead to decreased sitting time during the workday among sedentary office workers. Methods: A randomized cross-over trial was conducted from January to April, 2012 at a business in Minneapolis. 28 (nine men, 26 full-time) sedentary office workers took part in a 4 week intervention period which included the use of SSDs to gradually replace 50% of sitting time with standing during the workday. Physical activity was the primary outcome. Mood, energy level, fatigue, appetite, dietary intake, and productivity were explored as secondary outcomes. Results: The intervention reduced sitting time at work by 21% (95% CI 18%–25%) and sedentary time by 4.8 min/work-hr (95% CI 4.1–5.4 min/work-hr). For a 40 h work-week, this translates into replacement of 8 h of sitting time with standing and sedentary time being reduced by 3.2 h. Activity level during non-work hours did not change. The intervention also increased overall sense of well-being, energy, decreased fatigue, had no impact on productivity, and reduced appetite and dietary intake. The workstations were popular with the participants. Conclusion: The SSD intervention was successful in increasing work-time activity level, without changing activity level during non-work hours.

Low-intensity and moderate exercise training improves autonomic nervous system activity imbalanced by postnatal early overfeeding in rats

Background

Postnatal early overfeeding and physical inactivity are serious risk factors for obesity. Physical activity enhances energy expenditure and consumes fat stocks, thereby decreasing body weight (bw). This study aimed to examine whether low-intensity and moderate exercise training in different post-weaning stages of life is capable of modulating the autonomic nervous system (ANS) activity and inhibiting perinatal overfeeding-induced obesity in rats.

Methods

The obesity-promoting regimen was begun two days after birth when the litter size was adjusted to 3 pups (small litter, SL) or to 9 pups (normal litter, NL). The rats were organized into exercised groups as follows: from weaning until 90-day-old, from weaning until 50-day-old, or from 60- until 90-days-old. All experimental procedures were performed just one day after the exercise training protocol.

Results

The SL-no-exercised (SL-N-EXE) group exhibited excess weight and increased fat accumulation. We also observed fasting hyperglycemia and glucose intolerance in these rats. In addition, the SL-N-EXE group exhibited an increase in the vagus nerve firing rate, whereas the firing of the greater splanchnic nerve was not altered. Independent of the timing of exercise and the age of the rats, exercise training was able to significantly blocks obesity onset in the SL rats; even SL animals whose exercise training was stopped at the end of puberty, exhibited resistance to obesity progression. Fasting glycemia was maintained normal in all SL rats that underwent the exercise training, independent of the period. These results demonstrate that moderate exercise, regardless of the time of onset, is capable on improve the vagus nerves imbalanced tonus and blocks the onset of early overfeeding-induced obesity.

Conclusions

Low-intensity and moderate exercise training can promote the maintenance of glucose homeostasis, reduces the large fat pad stores associated to improvement of the ANS activity in adult rats that were obesity-programmed by early overfeeding.

Leanness and heightened nonresting energy expenditure: role of skeletal muscle activity thermogenesis

A high-calorie diet accompanied by low levels of physical activity (PA) accounts for the widespread prevalence of obesity today, and yet some people remain lean even in this obesogenic environment. Here, we investigate the cause for this exception. A key trait that predicts high PA in both humans and laboratory rodents is intrinsic aerobic capacity. Rats artificially selected as high-capacity runners (HCR) are lean and consistently more physically active than their low-capacity runner (LCR) counterparts; this applies to both males and females. Here, we demonstrate that HCR show heightened total energy expenditure (TEE) and hypothesize that this is due to higher nonresting energy expenditure (NREE; includes activity EE). After matching for body weight and lean mass, female HCR consistently had heightened nonresting EE, but not resting EE, compared with female LCR. Because of the dominant role of skeletal muscle in nonresting EE, we examined muscle energy use. We found that lean female HCR had higher muscle heat dissipation during activity, explaining their low economy of activity and high activity EE. This may be due to the amplified skeletal muscle expression levels of proteins involved in EE and reduced expression levels of proteins involved in energy conservation in HCR relative to LCR. This is also associated with an increased sympathetic drive to skeletal muscle in HCR compared with LCR. We find little support for the hypothesis that resting metabolic rate is correlated with maximal aerobic capacity if body size and composition are fully considered; rather, the critical factor appears to be activity thermogenesis.

Modelling olanzapine-induced weight gain in rats

The second-generation antipsychotic drug olanzapine has become a widely prescribed drug in the treatment of schizophrenia and bipolar disorder. Unfortunately, its therapeutic benefits are partly outweighed by significant weight gain and other metabolic side effects, which increase the risk for diabetes and cardiovascular disease. Because olanzapine remains superior to other antipsychotic drugs that show less weight gain liability, insight into the mechanisms responsible for olanzapine-induced weight gain is crucial if it is to be effectively addressed. Over the past few decades, several groups have investigated the effects of olanzapine on energy balance using rat models. Unfortunately, results from different studies have not always been consistent and it remains to be determined which paradigms should be used in order to model olanzapine-induced weight gain most accurately. This review summarizes the effects of olanzapine on energy balance observed in different rat models and discusses some of the factors that appear to contribute to the inconsistencies in observed effects. In addition it compares the effects reported in rats with clinical findings to determine the predictive validity of different paradigms.

The effect of non-exercise activity thermogenesis on subjects with metabolic syndrome - a proof of concept study in Qatar

Metabolic syndrome is a cluster of metabolic abnormalities that increases the risk of cardiovascular disease and type 2 diabetes. Total human energy expenditure is divided into three major components; resting metabolic rate, thermic effect of food, and activity thermogenesis which is divided into exercise and non exercise activity thermogenesis (NEAT). In this study, NEAT was used as a lifestyle intervention on subjects with metabolic syndrome. 200 eligible patients from the Diabetes and Endocrinology Department at Hamad Medical Hospital in Doha, Qatar were assigned to an intervention (n = 100) or control (n = 100) group and followed for one year. The intervention group was advised to practice NEAT enhancing activities, while the control group was not advised about NEAT. Measurements of waist circumference, weight, BMI, blood pressure, glucose and lipid profile were assessed at baseline, six months and 1 year.

After 1 year 52 intervention and 55 control subjects completed the study. The results revealed no statistically significant differences in metabolic syndrome components between the two randomized groups. The amount of recommended NEAT activity appears to have been too small to influence study outcomes. Future studies in similar populations may need to consider the high dropout rate, and use of incentives or other interventions to increase compliance and retention.

Subcongenic analysis of tabw2 obesity QTL on mouse chromosome 6

Background

We previously established a congenic mouse strain with TALLYHO/Jng (TH) donor segment on chromosome 6 in a C57BL/6 (B6) background that harbors an obesity quantitative trait locus, tabw2. The B6.TH-tabw2 congenic mice developed increased adiposity that became exacerbated upon feeding a high fat-high sucrose (HFS) diet. To fine map the tabw2, in this study we generated and characterized subcongenic lines with smaller TH donor segments.

Results

We fixed four subcongenic lines, with maximum size of donor segment retained in the lines ranging from 10.8 – 92.5 Mb. For mapping, all the subcongenic mice, along with B6.TH-tabw2 congenic and B6-homozygous control mice were fed either chow or HFS diets, and their post-mortem fat pads were weighed. Mice were also characterized for energy expenditure, respiratory exchange ratio, locomotor activity, and food intake. As previously reported, B6.TH-tabw2 congenic mice showed a significantly larger fat mass than controls on both diets. On chow, a subcongenic line retaining the distal region of the TH donor congenic interval exhibited significantly larger fat mass than B6-homozygous controls, and comparable that to B6.TH-tabw2 congenic mice. Two nested subcongenic lines within that region suggested that the effect of tabw2 on obesity could be attributed to at least two subloci. On HFS diets, on the other hand, all the subcongenic mice had significantly larger fat mass than controls without genotype differences, but none of them had fat mass as large as the original congenic mice. This possibly implicates that further genetic complexity involves in the effect of tabw2 on diet-induced obesity. Significantly reduced locomotor activity was exhibited in B6.TH-tabw2 congenic and subcongenic mice compared to controls when animals were fed HFS diets. B6.TH-tabw2 congenic mice, but not subcongenic mice, also had significantly increased food intake on HFS diets.

Conclusions

It appears that at least two subloci explaining the tabw2 effect under chow feeding map to the distal region of the congenic interval, whereas the diet-induced obesity mediated by tabw2 is attributed to more complex genetic mechanism.

Acutely decreased thermoregulatory energy expenditure or decreased activity energy expenditure both acutely reduce food intake in mice

Despite the suggestion that reduced energy expenditure may be a key contributor to the obesity pandemic, few studies have tested whether acutely reduced energy expenditure is associated with a compensatory reduction in food intake. The homeostatic mechanisms that control food intake and energy expenditure remain controversial and are thought to act over days to weeks. We evaluated food intake in mice using two models of acutely decreased energy expenditure: 1) increasing ambient temperature to thermoneutrality in mice acclimated to standard laboratory temperature or 2) exercise cessation in mice accustomed to wheel running. Increasing ambient temperature (from 21°C to 28°C) rapidly decreased energy expenditure, demonstrating that thermoregulatory energy expenditure contributes to both light cycle (40±1%) and dark cycle energy expenditure (15±3%) at normal ambient temperature (21°C). Reducing thermoregulatory energy expenditure acutely decreased food intake primarily during the light cycle (65±7%), thus conflicting with the delayed compensation model, but did not alter spontaneous activity. Acute exercise cessation decreased energy expenditure only during the dark cycle (14±2% at 21°C; 21±4% at 28°C), while food intake was reduced during the dark cycle (0.9±0.1 g) in mice housed at 28°C, but during the light cycle (0.3±0.1 g) in mice housed at 21°C. Cumulatively, there was a strong correlation between the change in daily energy expenditure and the change in daily food intake (R² = 0.51, p<0.01). We conclude that acutely decreased energy expenditure decreases food intake suggesting that energy intake is regulated by metabolic signals that respond rapidly and accurately to reduced energy expenditure.

Role of the hypothalamus in the neuroendocrine regulation of body weight and composition during energy deficit

Energy deficit in lean or obese animals or humans stimulates appetite, reduces energy expenditure and possibly also decreases physical activity, thereby contributing to weight regain. Often overlooked in weight loss trials for obesity, however, is the effect of energy restriction on neuroendocrine status. Negative energy balance in lean animals and humans consistently inhibits activity of the hypothalamo-pituitary-thyroid, -gonadotropic and -somatotropic axes (or reduces circulating insulin-like growth factor-1 levels), while concomitantly activating the hypothalamo-pituitary-adrenal axis, with emerging evidence of similar changes in overweight and obese people during lifestyle interventions for weight loss. These neuroendocrine changes, which animal studies show may result in part from hypothalamic actions of orexigenic (e.g. neuropeptide Y, agouti-related peptide) and anorexigenic peptides (e.g. alpha-melanocyte-stimulating hormone, and cocaine and amphetamine-related transcript), can adversely affect body composition by promoting the accumulation of adipose tissue (particularly central adiposity) and stimulating the loss of lean body mass and bone. As such, current efforts to maximize loss of excess body fat in obese people may inadvertently be promoting long-term complications such as central obesity and associated health risks, as well as sarcopenia and osteoporosis. Future weight loss trials would benefit from assessment of the effects on body composition and key hormonal regulators of body composition using sensitive techniques.

The use of a running wheel to measure activity in rodents: relationship to energy balance, general activity, and reward

Running wheels are commonly employed to measure rodent physical activity in a variety of contexts, including studies of energy balance and obesity. There is no consensus on the nature of wheel-running activity or its underlying causes, however. Here, we will begin by systematically reviewing how running wheel availability affects physical activity and other aspects of energy balance in laboratory rodents. While wheel running and physical activity in the absence of a wheel commonly correlate in a general sense, in many specific aspects the two do not correspond. In fact, the presence of running wheels alters several aspects of energy balance, including body weight and composition, food intake, and energy expenditure of activity. We contend that wheel-running activity should be considered a behavior in and of itself, reflecting several underlying behavioral processes in addition to a rodent's general, spontaneous activity. These behavioral processes include defensive behavior, predatory aggression, and depression- and anxiety-like behaviors. As it relates to energy balance, wheel running engages several brain systems-including those related to the stress response, mood, and reward, and those responsive to growth factors-that influence energy balance indirectly. We contend that wheel-running behavior represents factors in addition to rodents' tendency to be physically active, engaging additional neural and physiological mechanisms which can then independently alter energy balance and behavior. Given the impact of wheel-running behavior on numerous overlapping systems that influence behavior and physiology, this review outlines the need for careful design and interpretation of studies that utilize running wheels as a means for exercise or as a measurement of general physical activity.

Neuropeptides controlling energy balance: orexins and neuromedins

In this chapter, we review the feeding and energy expenditure effects of orexin (also known as hypocretin) and neuromedin. Orexins are multifunctional neuropeptides that affect energy balance by participating in regulation of appetite, arousal, and spontaneous physical activity. Central orexin signaling for all functions originates in the lateral hypothalamus-perifornical area and is likely functionally differentiated based on site of action and on interacting neural influences. The effect of orexin on feeding is likely related to arousal in some ways but is nonetheless a separate neural process that depends on interactions with other feeding-related neuropeptides. In a pattern distinct from other neuropeptides, orexin stimulates both feeding and energy expenditure. Orexin increases in energy expenditure are mainly by increasing spontaneous physical activity, and this energy expenditure effect is more potent than the effect on feeding. Global orexin manipulations, such as in transgenic models, produce energy balance changes consistent with a dominant energy expenditure effect of orexin. Neuromedins are gut-brain peptides that reduce appetite. There are gut sources of neuromedin, but likely the key appetite-related neuromedin-producing neurons are in the hypothalamus and parallel other key anorectic neuropeptide expression in the arcuate to paraventricular hypothalamic projection. As with other hypothalamic feeding-related peptides, hindbrain sites are likely also important sources and targets of neuromedin anorectic action. Neuromedin increases physical activity in addition to reducing appetite, thus producing a consistent negative energy balance effect. Together with the other various neuropeptides, neurotransmitters, neuromodulators, and neurohormones, neuromedin and orexin act in the appetite network to produce changes in food intake and energy expenditure, which ultimately influences the regulation of body weight.

Potential contributors to the canadian pediatric obesity epidemic

As a group, Canadian children and youth are heavier than at any time in the recent past. However, to date there has been no critical examination of the factors which are likely to have contributed to these deleterious trends. A review of the evidence suggests that there is robust evidence supporting the role of reduced sleep, increased sedentary time, increased consumption of sugar-sweetened beverages, and secular increases in adult obesity as contributing factors to the current epidemic of childhood obesity. There is moderate evidence that these trends are related to changes in either total energy intake or physical activity, while there is very little evidence supporting the role of maternal age, breastfeeding, exposure to endocrine disrupters, or inadequate calcium intake. These findings suggest that targeting sleep, sedentary time, and sugar-sweetened beverage intake in Canadian children and youth may help to prevent future weight gain at the population level.

Chronic AMP-kinase activation with AICAR reduces adiposity by remodeling adipocyte metabolism and increasing leptin sensitivity

This study investigated the effect of chronic AMP-kinase (AMPK) activation with 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) on white adipose tissue (WAT) metabolism and the implications for visceral (VC) and subcutaneous (SC) adiposity, whole body-energy homeostasis, and hypothalamic leptin sensitivity. Male Wistar rats received daily single intraperitoneal injections of either saline or AICAR (0.7g/kg body weight) for 4 and 8 weeks and were pair-fed throughout the study. AICAR-treated rats had reduced adiposity with increased mitochondrial density in VC and SC fat pads, which was accompanied by reduced circulating leptin and time-dependent and depot-specific regulation of AMPK phosphorylation and FA oxidation. Interestingly, the anorectic effect to exogenous leptin was more pronounced in AICAR-treated animals than controls. This corresponded to reductions in hypothalamic AMPK phosphorylation and suppressor of cytokine signaling 3 content, whereas signal transducer and activator of transcription 3 phosphorylation was either unchanged or increased at 4 and 8 weeks in AICAR-treated rats. Ambulatory activity and whole-body energy expenditure (EE) were also increased with AICAR treatment. Altogether, chronic AICAR-induced AMPK activation increased WAT oxidative machinery, whole-body EE, and hypothalamic leptin sensitivity. This led to significant reductions in VC and SC adiposity without inducing energy-sparing mechanisms that oppose long-term fat loss.

Analysis of time-dependent adaptations in whole-body energy balance in obesity induced by high-fat diet in rats

Background

High-fat (HF) diet has been extensively used as a model to study metabolic disorders of human obesity in rodents. However, the adaptive whole-body metabolic responses that drive the development of obesity with chronically feeding a HF diet are not fully understood. Therefore, this study investigated the physiological mechanisms by which whole-body energy balance and substrate partitioning are adjusted in the course of HF diet-induced obesity.

Methods

Male Wistar rats were fed ad libitum either a standard or a HF diet for 8 weeks. Food intake (FI) and body weight were monitored daily, while oxygen consumption, respiratory exchange ratio, physical activity, and energy expenditure (EE) were assessed weekly. At week 8, fat mass and lean body mass (LBM), fatty acid oxidation and uncoupling protein-1 (UCP-1) content in brown adipose tissue (BAT), as well as acetyl-CoA carboxylase (ACC) content in liver and epidydimal fat were measured.

Results

Within 1 week of ad libitum HF diet, rats were able to spontaneously reduce FI to precisely match energy intake of control rats, indicating that alterations in dietary energy density were rapidly detected and FI was self-regulated accordingly. Oxygen consumption was higher in HF than controls throughout the study as whole-body fat oxidation also progressively increased. In HF rats, EE initially increased, but then reduced as dark cycle ambulatory activity reached values ~38% lower than controls. No differences in LBM were detected; however, epidydimal, inguinal, and retroperitoneal fat pads were 1.85-, 1.89-, and 2.54-fold larger in HF-fed than control rats, respectively. Plasma leptin was higher in HF rats than controls throughout the study, indicating the induction of leptin resistance by HF diet. At week 8, UCP-1 content and palmitate oxidation in BAT were 3.1- and 1.5-fold higher in HF rats than controls, respectively, while ACC content in liver and epididymal fat was markedly reduced.

Conclusion

The thermogenic response induced by the HF diet was offset by increased energy efficiency and time-dependent reduction in physical activity, favoring fat accumulation. These adaptations were mainly driven by the nutrient composition of the diet, since control and HF animals spontaneously elicited isoenergetic intake.

Increased energy expenditure and leptin sensitivity account for low fat mass in myostatin-deficient mice

Myostatin deficiency causes dramatically increased skeletal muscle mass and reduced fat mass. Previously, myostatin-deficient mice were reported to have unexpectedly low total energy expenditure (EE) after normalizing to body mass, and thus, a metabolic cause for low fat mass was discounted. To clarify how myostatin deficiency affects the control of body fat mass and energy balance, we compared rates of oxygen consumption, body composition, and food intake in young myostatin-deficient mice relative to wild-type (WT) and heterozygous (HET) controls. We report that after adjusting for total body mass using regression analysis, young myostatin-deficient mice display significantly increased EE relative to both WT (+0.81 ± 0.28 kcal/day, P = 0.004) and HET controls (+0.92 ± 0.31 kcal/day, P = 0.005). Since food intake was not different between groups, increased EE likely accounts for the reduced body fat mass (KO: 8.8 ± 1.1% vs. WT: 14.5 ± 1.3%, P = 0.003) and circulating leptin levels (KO: 0.7 ± 0.2 ng/ml vs. WT: 1.9 ± 0.3 ng/ml, P = 0.008). Interestingly, the observed increase in adjusted EE in myostatin-deficient mice occurred despite dramatically reduced ambulatory activity levels (-50% vs. WT, P < 0.05). The absence of hyperphagia together with increased EE in myostatin-deficient mice suggests that increased leptin sensitivity may contribute to their lean phenotype. Indeed, leptin-induced anorexia (KO: -17 ± 1.2% vs. WT: -5 ± 0.3%) and weight loss (KO: -2.2 ± 0.2 g vs. WT: -1.6 ± 0.1, P < 0.05) were increased in myostatin-deficient mice compared with WT controls. We conclude that increased EE, together with increased leptin sensitivity, contributes to low fat mass in mice lacking myostatin.

Identification of a physiological role for leptin in the regulation of ambulatory activity and wheel running in mice

Mechanisms regulating spontaneous physical activity remain poorly characterized despite evidence of influential genetic and acquired factors. We evaluated ambulatory activity and wheel running in leptin-deficient ob/ob mice and in wild-type mice rendered hypoleptinemic by fasting in both the presence and absence of subcutaneous leptin administration. In ob/ob mice, leptin treatment to plasma levels characteristic of wild-type mice acutely increased both ambulatory activity (by 4,000 ± 200 beam breaks/dark cycle, P < 0.05) and total energy expenditure (TEE; by 0.11 ± 0.01 kcal/h during the dark cycle, P < 0.05) in a dose-dependent manner and acutely increased wheel running (+350%, P < 0.05). Fasting potently increased ambulatory activity and wheel running in wild-type mice (AA: +25%, P < 0.05; wheel running: +80%, P < 0.05), and the effect of fasting was more pronounced in ob/ob mice (AA: +400%, P < 0.05; wheel running: +1,600%, P < 0.05). However, unlike what occurred in ad libitum-fed ob/ob mice, physiological leptin replacement attenuated or prevented fasting-induced increases of ambulatory activity and wheel running in both wild-type and ob/ob mice. Thus, plasma leptin is a physiological regulator of spontaneous physical activity, but the nature of leptin's effect on activity is dependent on food availability.

The biological control of voluntary exercise, spontaneous physical activity and daily energy expenditure in relation to obesity: human and rodent perspectives

Mammals expend energy in many ways, including basic cellular maintenance and repair, digestion, thermoregulation, locomotion, growth and reproduction. These processes can vary tremendously among species and individuals, potentially leading to large variation in daily energy expenditure (DEE). Locomotor energy costs can be substantial for large-bodied species and those with high-activity lifestyles. For humans in industrialized societies, locomotion necessary for daily activities is often relatively low, so it has been presumed that activity energy expenditure and DEE are lower than in our ancestors. Whether this is true and has contributed to a rise in obesity is controversial. In humans, much attention has centered on spontaneous physical activity (SPA) or non-exercise activity thermogenesis (NEAT), the latter sometimes defined so broadly as to include all energy expended due to activity, exclusive of volitional exercise. Given that most people in Western societies engage in little voluntary exercise, increasing NEAT may be an effective way to maintain DEE and combat overweight and obesity. One way to promote NEAT is to decrease the amount of time spent on sedentary behaviours (e.g. watching television). The effects of voluntary exercise on other components of physical activity are highly variable in humans, partly as a function of age, and have rarely been studied in rodents. However, most rodent studies indicate that food consumption increases in the presence of wheels; therefore, other aspects of physical activity are not reduced enough to compensate for the energetic cost of wheel running. Most rodent studies also show negative effects of wheel access on body fat, especially in males. Sedentary behaviours per se have not been studied in rodents in relation to obesity. Several lines of evidence demonstrate the important role of dopamine, in addition to other neural signaling networks (e.g. the endocannabinoid system), in the control of voluntary exercise. A largely separate literature points to a key role for orexins in SPA and NEAT. Brain reward centers are involved in both types of physical activities and eating behaviours, likely leading to complex interactions. Moreover, voluntary exercise and, possibly, eating can be addictive. A growing body of research considers the relationships between personality traits and physical activity, appetite, obesity and other aspects of physical and mental health. Future studies should explore the neurobiology, endocrinology and genetics of physical activity and sedentary behaviour by examining key brain areas, neurotransmitters and hormones involved in motivation, reward and/or the regulation of energy balance.

Do all sedentary activities lead to weight gain: sleep does not

PURPOSE OF REVIEW

To discuss the benefits of having a good night's sleep for body weight stability.

RECENT FINDINGS

Experimental studies have shown that short-term partial sleep restriction decreases glucose tolerance, increases sympathetic tone, elevates cortisol concentrations, decreases the satiety hormone leptin, increases the appetite-stimulating hormone ghrelin, and increases hunger and appetite. Short sleep duration might increase the risk of becoming obese, because it does not allow the recovery of a hormonal profile facilitating appetite control. Lack of sleep could also lead to weight gain and obesity by increasing the time available for eating and by making the maintenance of a healthy lifestyle more difficult. Furthermore, the increased fatigue and tiredness associated with sleeping too little could lessen one's resolve to follow exercise regimens.

SUMMARY

Short sleep duration appears to be a novel and independent risk factor for obesity. With the growing prevalence of chronic sleep restriction, any causal association between reduced sleep and obesity would have substantial importance from a public health standpoint. Future research is needed to determine whether sleep extension in sleep-deprived obese individuals will influence appetite control and/or reduce the amount of body fat.

Energy expenditure in obesity-prone and obesity-resistant rats before and after the introduction of a high-fat diet

While most rats gain weight when placed on a high-fat diet (HFD), some strains resist HFD-induced weight gain. To maintain weight, obesity-resistant (OR) rats must either eat less than obesity-prone (OP) rats or increase total energy expenditure (TEE). To determine if changes in TEE predispose to or protect from weight gain, energy expenditure, energy intake, and weight gain were measured in male and female OP and OR rats consuming a low-fat diet (LFD) and for 5 days after switching to a HFD. After 5 days on a HFD, OP rats gained significantly more weight (male: 42.8 ± 6.9 g, female: 25.5 ± 3.0 g) than their OR counterparts (male: 24.0 ± 7.5 g, female: 13.7 ± 1.4 g). Both male and female rats significantly increased their energy intake when transitioned to the HFD, and TEE increased modestly in all groups. Compared with female OP rats, female OR rats had a significantly greater increase in TEE on the HFD. This was due to an increase in both resting and nonresting energy expenditure. In contrast, the effect of the HFD in males was minor. TEE was also measured in female rats consuming a HFD, pair fed to LFD calories. The increase in TEE of pair-fed female OR rats was substantially less than what was seen in the HFD ad libitum condition. Physical activity was also measured in female rats. There was no evidence that increases in physical activity were the cause of the increased TEE seen in female OR rats consuming a HFD. These results suggest that resistance to HFD-induced weight gain in female OR rats may be due in part to an increase in TEE and a greater reliance on lipid as an energy source. Changes in TEE appear to be triggered by overconsumption of the HFD and not simply the diet composition.

Spontaneous activity, economy of activity, and resistance to diet-induced obesity in rats bred for high intrinsic aerobic capacity

Though obesity is common, some people remain resistant to weight gain even in an obesogenic environment. The propensity to remain lean may be partly associated with high endurance capacity along with high spontaneous physical activity and the energy expenditure of activity, called non-exercise activity thermogenesis (NEAT). Previous studies have shown that high-capacity running rats (HCR) are lean compared to low-capacity runners (LCR), which are susceptible to cardiovascular disease and metabolic syndrome. Here, we examine the effect of diet on spontaneous activity and NEAT, as well as potential mechanisms underlying these traits, in rats selectively bred for high or low intrinsic aerobic endurance capacity. Compared to LCR, HCR were resistant to the sizeable increases in body mass and fat mass induced by a high-fat diet; HCR also had lower levels of circulating leptin. HCR were consistently more active than LCR, and had lower fuel economy of activity, regardless of diet. Nonetheless, both HCR and LCR showed a similar decrease in daily activity levels after high-fat feeding, as well as decreases in hypothalamic orexin-A content. The HCR were more sensitive to the NEAT-activating effects of intra-paraventricular orexin-A compared to LCR, especially after high-fat feeding. Lastly, levels of cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) in the skeletal muscle of HCR were consistently higher than LCR, and the high-fat diet decreased skeletal muscle PEPCK-C in both groups of rats. Differences in muscle PEPCK were not secondary to the differing amount of activity. This suggests the possibility that intrinsic differences in physical activity levels may originate at the level of the skeletal muscle, which could alter brain responsiveness to neuropeptides and other factors that regulate spontaneous daily activity and NEAT.

Obesity is a sign - over-eating is a symptom: an aetiological framework for the assessment and management of obesity

Obesity is characterized by the accumulation of excess body fat and can be conceptualized as the physical manifestation of chronic energy excess. Using the analogy of oedema, the consequence of positive fluid balance or fluid retention, obesity can be seen as the consequence of positive energy balance or calorie 'retention'. Just as the assessment of oedema requires a comprehensive assessment of factors related to fluid balance, the assessment of obesity requires a systematic assessment of factors potentially affecting energy intake, metabolism and expenditure. Rather than just identifying and describing a behaviour ('this patient eats too much'), clinicians should seek to identify the determinants of this behaviour ('why, does this patient eat too much?'). This paper provides an aetiological framework for the systematic assessment of the socio-cultural, biomedical, psychological and iatrogenic factors that influence energy input, metabolism and expenditure. The paper discusses factors that affect metabolism (age, sex, genetics, neuroendocrine factors, sarcopenia, metabolically active fat, medications, prior weight loss), energy intake (socio-cultural factors, mindless eating, physical hunger, emotional eating, mental health, medications) and activity (socio-cultural factors, physical and emotional barriers, medications). It is expected that the clinical application of this framework can help clinicians systematically assess, identify and thereby address the aetiological determinants of positive energy balance resulting in more effective obesity prevention and management.

Running behavior and its energy cost in mice selectively bred for high voluntary locomotor activity

Locomotion is central to behavior and intrinsic to many fitness-critical activities (e.g., migration, foraging), and it competes with other life-history components for energy. However, detailed analyses of how changes in locomotor activity and running behavior affect energy budgets are scarce. We quantified these effects in four replicate lines of house mice that have been selectively bred for high voluntary wheel running (S lines) and in their four nonselected control lines (C lines). We monitored wheel speeds and oxygen consumption for 24-48 h to determine daily energy expenditure (DEE), resting metabolic rate (RMR), locomotor costs, and running behavior (bout characteristics). Daily running distances increased roughly 50%-90% in S lines in response to selection. After we controlled for body mass effects, selection resulted in a 23% increase in DEE in males and a 6% increase in females. Total activity costs (DEE - RMR) accounted for 50%-60% of DEE in both S and C lines and were 29% higher in S males and 5% higher in S females compared with their C counterparts. Energetic costs of increased daily running distances differed between sexes because S females evolved higher running distances by running faster with little change in time spent running, while S males also spent 40% more time running than C males. This increase in time spent running impinged on high energy costs because the majority of running costs stemmed from "postural costs" (the difference between RMR and the zero-speed intercept of the speed vs. metabolic rate relationship). No statistical differences in these traits were detected between S and C females, suggesting that large changes in locomotor behavior do not necessarily effect overall energy budgets. Running behavior also differed between sexes: within S lines, males ran with more but shorter bouts than females. Our results indicate that selection effects on energy budgets can differ dramatically between sexes and that energetic constraints in S males might partly explain the apparent selection limit for wheel running observed for over 15 generations.

Maturity-related differences in physical activity among 10- to 12-year-old girls

Besides environmental and psycho-social factors explaining the variation in physical activity levels during adolescence, some evidence suggests that biological processes are involved in regulating habitual daily physical activity and energy expenditure. The purpose of this study was to examine the influence of biological maturity status on physical activity. Chronological age, standing height, sitting height, and body mass were measured cross-sectionally in 268 girls, aged 9.5 to 11.5 years. Biological maturity groups (Early, Average, Late) were created according to estimated age at peak-height-velocity (estAPHV). Habitual physical activity was determined with a pedometer (Yamax Digiwalker SW-200) over a 7-day period. Differences in steps/day across maturity groups were examined by ANCOVA, controlling separately for time the pedometer was worn, leg length, and body mass. Mean pedometer steps/day was 10,822 +/- 2,639. As expected, body size varied by maturity status (e.g., early > average > late). Significant maturity group differences were found with early maturing girls showing lower activity levels compared to average or late maturers. These differences remained after controlling for time the pedometer was worn and leg length; however, the differences were no longer significant when controlling for body mass. The results suggest that biological maturity status influences physical activity levels in girls between 10 and 12 years of age but the relationship is not independent of body mass. Further research is needed to establish the complex inter-relationships among adiposity, biological maturation, and energy expenditure during puberty.

Daily intraparaventricular orexin-A treatment induces weight loss in rats

The neuropeptide orexin (hypocretin) increases energy expenditure partially through increasing spontaneous physical activity. The ability of exogenous orexin to alter body weight has never been established, however. We sought to determine whether orexin-A microinjected into the paraventricular nucleus of the hypothalamus (PVN) induced weight loss in rats. Chronic guide cannulae were implanted into rats, aimed at the PVN. Rats were given daily microinjections of orexin (0.5 nmol) or vehicle into the PVN for 6 days; food intake and body weight were measured daily. In a separate group of rats, we injected orexin-A and vehicle intra-PVN and measured daily activity levels. Daily orexin treatment induced weight loss: orexin-A-treated rats lost significantly more weight than their vehicle-injected counterparts without a significant difference in food intake. Rats were significantly more active after intra-PVN orexin compared to vehicle. These results support the concept that orexinergic agents have the potential to produce negative energy balance through increasing physical activity. This presents a promising, untapped potential resource for weight loss.

Endurance capacity, not body size, determines physical activity levels: role of skeletal muscle PEPCK

Some people remain lean despite pressure to gain weight. Lean people tend to have high daily activity levels, but the source of this increased activity is unknown. We found that leanness cannot be accounted for by increased weight-corrected food intake in two different types of lean rats. As previously reported in lean people, we found that lean rats had higher daily activity levels; lean rats also expended more energy. These lean rats were developed through artificial selection for high aerobic endurance capacity. To test whether our findings extended to a human population, we measured endurance capacity using a VO_2max treadmill test and daily activity in a group of non-exercising individuals. Similar to lean rats selectively bred for endurance capacity, our study revealed that people with higher VO_2max also spent more time active throughout the day. Hence, endurance capacity may be the trait that underlies both physical activity levels and leanness. We identified one potential mechanism for the lean, active phenotype in rats, namely high levels of skeletal muscle PEPCK. Therefore, the lean phenotype is characterized by high endurance capacity and high activity and may stem from altered skeletal muscle energetics.

Day-to-day variability in voluntary wheel running among genetically differentiated lines of mice that vary in activity level

This study examined the day-to-day variability in voluntary wheel-running behavior among three genetically distinct lines of young male and female mice. Daily wheel revolutions were recorded at an age of 6-8 weeks in 10 males and 10 females from each of 3 lines: selectively bred line for high wheel running (Line 8), selectively bred for high wheel-running activity and fixed for a Mendelian recessive allele that reduces hind-limb muscle mass by 50% (Line 3), non-selected control (Line 2). There were significant mean differences in revolutions/day among weeks (P = 0.003), but the effect size was small (10%). Significant main effects for wheel running were also revealed for sex and line (P < 0.001). The grand mean +/- SD for the coefficient of variation (CV) of intra-individual wheel running was 23.0 +/- 10.8%. Although a significant main effect for the CV was found for week, the effect size was low (7%) (age 6 weeks, 23.4 +/- 10.9%; age 7 weeks, 25.1 +/- 13.2%; age 8 weeks, 20.1 +/- 7.8%). The overall mean CV was similar between females (21.4 +/- 9.8%) and males (24.4 +/- 12.0%) and among lines (Line 2, 23.4 +/- 9.8%; Line 3, 20.4 +/- 7.6%; and Line 8, 25.0 +/- 14.4%). These findings are consistent with our previous work in young humans and lend further support for the hypothesis that biological mechanisms influence daily levels of physical activity.

Bariatric surgery: a history of empiricism, a future in science

BACKGROUND

The observation that obesity can be successfully treated by gastrointestinal surgery is a tribute to the innovative efforts by determined surgeons and the ever improving safety of general anesthesia. Yet as the body of knowledge and discovery on the root causes of human obesity accumulate, surgical approaches to treat morbid obesity are likely to change dramatically. While there is little doubt that dramatic weight loss can be achieved by surgically creating volume and absorption limitation to the reservoir and digestive functions of the gastrointestinal tract, human progress to more processed foods, less physical activity, and the pervasive public opinion that obesity is self-imposed are major obstacles to more widespread application of this approach.

DISCUSSION

Here we provide a mechanico-physiologic analysis of current operations, their rationale and limitations, as well as a glimpse of how future interventions might develop as a result of current knowledge in the field. The future of bariatric surgery is discussed in the context of these emerging technologies and in the context of the politics of obesity.

Kv1.3 gene-targeted deletion alters longevity and reduces adiposity by increasing locomotion and metabolism in melanocortin-4 receptor-null mice

OBJECTIVE

Gene-targeted deletion of the voltage-gated potassium channel, Kv1.3, results in 'super-smeller' mice that have altered firing patterns of mitral cells in the olfactory bulb, modified axonal targeting to glomerular synaptic units, and behaviorally have an increased ability to detect and discriminate odors. Moreover, the Kv1.3-null mice weighed less than their wild-type counterparts, have modified ingestive behaviors, and are resistant to fat deposition following a moderately high-fat dietary regime. In this study, we investigate whether or not gene-targeted deletion of Kv1.3 (Shaker family member) can abrogate weight gain in a genetic model of obesity, the melanocortin-4 receptor-null mouse (MC4R-null).

DESIGN

Mice with double gene-targeted deletions of Kv1.3 and MC4R were generated by interbreeding Kv1.3 (Kv)- and MC4R-null mouse lines to homozygosity. Developmental weights, nose to anus length, fat pad weight, fasting serum chemistry, oxygen consumption, carbon dioxide respiration, locomotor activity and caloric intake were monitored in control, Kv-null, MC4R-null and Kv/MC4R-null mice. Physiological and metabolic profiles were acquired at postnatal day 60 (P60) in order to explore changes linked to body weight at the reported onset of obesity in the MC4R-null model.

RESULTS

Gene-targeted deletion of Kv1.3 in MC4R-null mice reduces body weight by decreasing fat deposition and subsequent fasting leptin levels, without changing the overall growth, fasting blood glucose or serum insulin. Gene-targeted deletion of Kv1.3 in MC4R-null mice significantly extended lifespan and increased reproductive success. Basal or light-phase mass-specific metabolic rate and locomotor activity were not affected by genetic deletion of Kv1.3 in MC4R-null mice but dark-phase locomotor activity and mass-specific metabolism were significantly increased resulting in increased total energy expenditure.

CONCLUSIONS

Gene-targeted deletion of Kv1.3 can reduce adiposity and total body weight in a genetic model of obesity by increasing both locomotor activity and mass-specific metabolism.