Lower Resting Metabolic Rate Research Articles

Huddling remodels gut microbiota to reduce energy requirements in a small mammal species during cold exposure

BackgroundHuddling is highly evolved as a cooperative behavioral strategy for social mammals to maximize their fitness in harsh environments. Huddling behavior can change psychological and physiological responses. The coevolution of mammals with their microbial communities confers fitness benefits to both partners. The gut microbiome is a key regulator of host immune and metabolic functions. We hypothesized that huddling behavior altered energetics and thermoregulation by shaping caecal microbiota in small herbivores. Brandt’s voles (Lasiopodomys brandtii) were maintained in a group (huddling) or as individuals (separated) and were exposed to warm (23 ± 1 °C) and cold (4 ± 1 °C) air temperatures (Ta).ResultsVoles exposed to cold Ta had higher energy intake, resting metabolic rate (RMR) and nonshivering thermogenesis (NST) than voles exposed to warm Ta. Huddling voles had lower RMR and NST than separated voles in cold. In addition, huddling voles had a higher surface body temperature (Tsurface), but lower core body temperature (Tcore) than separated voles, suggesting a lower set-point of Tcore in huddling voles. Both cold and huddling induced a marked variation in caecal bacterial composition, which was associated with the lower Tcore. Huddling voles had a higher α and β-diversity, abundance of Lachnospiraceae and Veillonellaceae, but lower abundance of Cyanobacteria, Tenericutes, TM7, Comamonadaceae, and Sinobacteraceae than separated voles. Huddling or cold resulted in higher concentrations of short-chain fatty acids (SCFAs), particularly acetic acid and butyric acid when compared to their counterparts. Transplantation of caecal microbiota from cold-separated voles but not from cold-huddling voles induced significant increases in energy intake and RMR compared to that from warm-separated voles.ConclusionsThese findings demonstrate that the remodeling of gut microbiota, which is associated with a reduction in host Tcore, mediates cold- and huddling-induced energy intake and thermoregulation and therefore orchestrates host metabolic and thermal homeostasis. It highlights the coevolutionary mechanism of host huddling and gut microbiota in thermoregulation and energy saving for winter survival in endotherms.

Difference in plasticity of resting metabolic rate - the proximate explanation to different niche breadth in sympatric Ficedula flycatchers.

Variation in relative fitness of competing recently formed species across heterogeneous environments promotes coexistence. However, the physiological traits mediating such variation in relative fitness have rarely been identified. Resting metabolic rate (RMR) is tightly associated with life history strategies, thermoregulation, diet use, and inhabited latitude and could therefore moderate differences in fitness responses to fluctuations in local environments, particularly when species have adapted to different climates in allopatry. We work in a long‐term study of collared (Ficedula albicollis) and pied flycatchers (Ficedula hypoleuca) in a recent hybrid zone located on the Swedish island of Öland in the Baltic Sea. Here, we explore whether differences in RMR match changes in relative performance of growing flycatcher nestlings across environmental conditions using an experimental approach. The fitness of pied flycatchers has previously been shown to be less sensitive to the mismatch between the peak in food abundance and nestling growth among late breeders. Here, we find that pied flycatcher nestlings have lower RMR in response to higher ambient temperatures (associated with low food availability). We also find that experimentally relaxed nestling competition is associated with an increased RMR in this species. In contrast, collared flycatcher nestlings did not vary their RMR in response to these environmental factors. Our results suggest that a more flexible nestling RMR in pied flycatchers is responsible for the better adaptation of pied flycatchers to the typical seasonal changes in food availability experienced in this hybrid zone. Generally, subtle physiological differences that have evolved when species were in allopatry may play an important role to patterns of competition, coexistence, or displacements between closely related species in secondary contact.

Variants in the PPARGC1A Gene may Influence the Effect of Fat Intake on Resting Metabolic Rate in Obese Women.

Recent studies have shown that dietary intake and genetic variants play a decisive role in the risk of obesity. Therefore, this study was designed to examine the interaction between dietary fat and PPARGC1A polymorphisms on the level of resting metabolic rate (RMR). We enrolled 288 Iranian overweight and obese women in this cross-sectional study. We sequenced the 648 b.p. DNA in Exon 8 of PPARGC1A gene. We analyzed the two single-nucleotide polymorphisms, namely rs11290186 and rs2970847, in this region. All participants were assessed for RMR, dietary intake, and body composition. This study demonstrated that total cholesterol and insulin levels were positively associated with T allele carriers of rs2970847. Moreover, the A-deletion allele carrier of the rs11290186 genotype had higher triacylglycerol and insulin concentrations. The current study revealed that, after adjustment for energy intake, the AA genotype of PPARGC1A (rs11290186) had a direct association with polyunsaturated fatty acids and linoleic acid intakes. Another important finding in our study was that there was an interaction seen between fat and saturated fatty acids intake with the PPARGC1A genotypes. Women with fat intakes of more than 30% of calorie intake per day and the A-deletion genotype had a lower RMR and RMR/fat free mass (FFM). It seems that the PPARGC1A polymorphisms lead to the downregulation of insulin signaling and subsequently insulin resistance. In addition, the interactions between the PPARGC1A polymorphisms (rs11290186) and the level of dietary fat intake probably can have an effect on RMR and RMR/FFM in obese women.

Evaluation of a short protocol for indirect calorimetry in females with eating disorders and healthy controls

To enable clinicians to identify the clinical picture and treatment progress and to adjust eating plans according to personal energy needs, it is important to know the patient's correct resting metabolic rate (RMR). Indirect calorimetry (IC) is the preferred method for assessment of RMR, but long duration of measurement increases the load on the patients, and reduces the effectiveness in clinical and scientific settings. Further; not all patients reach a valid RMR according to the suggested best practice protocol, with 5min of steady state (SS) where respiratory gas volume exchange varies less than 10%. The aim of this study was to evaluate the possibility for an abbreviated RMR protocol and SS criterion. Forty two women diagnosed with bulimia nervosa or binge eating disorder (eating disorder group, ED), originally recruited for an outpatient treatment study, and 26 age and gender matched healthy controls (HC) were studied during a single, prolonged IC measurement. Participants rested for 10min in supine position wearing a two-way breathing facemask, before a continuous measurement period of 20min. Results from a standard 5min SS criterion was compared to an abbreviated 3min SS criterion. Both SS-criteria were evaluated through three different SS protocols (<10% variation in respiratory gas exchange), being: 1) measurement during the first 3 or 5min, 2) measurement after discarding the first 5min, and 3) the lowest identified RMR during the 20min of measurement. About 50% of the participants reached an early SS in both the defined SS minute criteria. Participants reaching a valid SS throughout the 20min of measurement increased from ∼90% to 100% with an abbreviated 3min SS. With a 5min SS criterion, the median (range) RMR for the 3 protocols were 1639.9 (1239.2), 1508.8 (1457.6) and 1500.6 (1328.8) respectively for the ED group, and 1702.2 (1239.4), 1608.4 (1076.4) and 1594.8 (1029.2) respectively for the HC group, (p>0.05 for all between-group analysis). With a 3min SS criterion, the median (range) RMR were 1533.6 (1298.2), 1461.2 (1406.1), and 1395.8 (1447.3) respectively for the ED group and 1681.7 (1332.4), 1613.7 (1266.0) and 1523.1 (1050.3), respectively for the HC group, (p>0.05 for all between-group analysis). Lowest measured RMR was different compared to the other two SS protocols in both the ED- and the HC group, and for both the 5min- and the 3min SS criteria, respectively (p<0.04). Furthermore, a SS of 3min resulted in lower RMR compared to 5min SS (p<0.00) and an increased number of participants classified as hypo-metabolic (RMRmeasured/RMRcalculated<0.9). An abbreviated measurement protocol to identify the lowest RMR using IC was not successful. Abbreviating the SS criteria from 5 to 3min, resulted in a lower RMR, hence encouraging further examination of the validity of shorter SS criterion than practiced today. Registered in Clinical Trials by id-number NCT02079935, and approved by the Norwegian Regional Committee for Medical and Health Research Ethics with id-number 2013/1871. The trial in which control persons were recruited, is approved by the Norwegian Regional Committees for Medical and Health Research Ethics with the id-number 2016/1718, and prospectively registered in Clinical Trials with the id-number NCT03007459.

A Genome-Wide Association Study Using a Custom Genotyping Array Identifies Variants in GPR158 Associated With Reduced Energy Expenditure in American Indians.

Pima Indians living in Arizona have a high prevalence of obesity, and we have previously shown that a relatively lower energy expenditure (EE) predicts weight and fat mass gain in this population. EE is a familial trait (heritability = 0.52); therefore, in the current study, we aimed to identify genetic variants that affect EE and thereby influence BMI and body fatness in Pima Indians. Genotypic data from 491,265 variants were analyzed for association with resting metabolic rate (RMR) and 24-h EE assessed in a whole-room calorimeter in 507 and 419 Pima Indians, respectively. Variants associated with both measures of EE were analyzed for association with maximum BMI and percent body fat (PFAT) in 5,870 and 912 Pima Indians, respectively. rs11014566 nominally associated with both measures of EE and both measures of adiposity in Pima Indians, where the G allele (frequency: Pima Indians = 0.60, Europeans <0.01) associated with lower 24-h EE (β = −33 kcal/day per copy), lower RMR (β = −31 kcal/day), higher BMI (β = +0.6 kg/m2), and higher PFAT (β = +0.9%). However, the association of rs11014566 with BMI did not directionally replicate when assessed in other ethnic groups. rs11014566 tags rs144895904, which affected promoter function in an in vitro luciferase assay. These variants map to GPR158, which is highly expressed in the brain and interacts with two other genes (RGS7 and CACNA1B) known to affect obesity in knockout mice. Our results suggest that common ethnic-specific variation in GPR158 may influence EE; however, its role in weight gain remains controversial, as it either had no association with BMI or associated with BMI but in the opposite direction in other ethnic groups.

The associations of resting metabolic rate with chronic conditions and weight loss.

The aim of this study was to examine the associations between baseline and changes in resting metabolic rate (RMR) with chronic condition(s) and weight loss (WL). Sex stratified analysis was undertaken on 393 adults from the Wharton Weight Management Clinics. The association between baseline RMR and WL was examined adjusting for age, BMI, ethnicity and treatment time. The association between changes in RMR (ΔRMR) and WL was also examined adjusting for baseline RMR and above covariates. Models were further adjusted for high glucose, triglycerides, blood pressure, low-density lipoprotein (LDL) and low high-density lipoprotein (HDL). While men (6.0 ± 8.6 kg) and women (5.6 ± 8.3 kg) had significant WL throughout the intervention, their measured decreases in RMR (-48 ± 322 kcal and -5 ± 322 kcal, respectively) were non-significant (P > 0.05). Individuals with a high blood pressure had a higher baseline RMR and women with a high LDL had a lower baseline RMR than those without the chronic condition (P < 0.05). Regardless of sex, WL was not significantly associated with baseline RMR or ΔRMR (P > 0.05) in both models. Participants with a low baseline RMR do not appear to be at a disadvantage for WL. Further, WL can occur without decreases in RMR in populations with high levels of obesity and obesity-related comorbidities.

Cold and Spleen-Qi Deficiency Patterns in Korean Medicine Are Associated with Low Resting Metabolic Rate.

Background. Korean medicine (KM) patterns such as cold, heat, deficiency, and excess patterns have been associated with alterations of resting metabolic rate (RMR). However, the association of KM patterns with accurately measured body metabolic rate has not been investigated. Methods. Data on cold (CP), heat (HP), spleen-qi deficiency (SQDP), and kidney deficiency (KDP) patterns were extracted by a factor analysis of symptoms experienced by 954 participants. A multiple regression analysis was conducted to determine the association between KM patterns and RMR measured by an indirect calorimeter. Results. The CP and SQDP scores were higher and the HP score was lower in women. The HP and SQDP scores decreased with age, while KDP scores increased with age. A multiple regression analysis revealed that CP and SQDP scores were negatively associated with RMR independently of gender and age, and the CP remained significantly and negatively associated with RMR even after adjustment for fat-free mass. Conclusions. The underlying pathology of CP and SQDP might be associated with the body's metabolic rate. Further studies are needed to investigate the usefulness of RMR measurement in pattern identification and the association of CP and SQDP with metabolic disorders.

Compare the resting metabolic rate status in the healthy metabolically obese with the unhealthy metabolically obese participants

BackgroundMetabolic abnormalities are usually linked with obesity; however, all obese people may not be affected by this condition. It has been indicated that obese people with higher resting metabolic rate (RMR) had an overall better metabolic profile than observed in those with low RMR. This study aimed to compare the RMR status of metabolically healthy (MHO) and unhealthy obese (MUHO). DesignCross-sectional sample of 226 obese women (BMI > 30 kg/m2) aged 17–69 years participated in the study. Participants were classified as MHO and MUHO. Metabolic health status was defined using Karelis definition. Metabolic profile, RMR, and body composition were examined. ResultMHO participants showed more favorable lipid profile, had reduced insulin resistance and lower total fat percentage and fat mass. RMR per BMI was 25% higher in the MHO group compared to the MUHO subjects. Interestingly by adding RMR/kg in the binary regression model for finding the modulatory role of RMR on the Karelis criteria, no significant difference was observed anymore regarding the Homeostasis Model Assessment (HOMA) between the MHO and MUHO participants. ConclusionIn this study we did not observe any major effects of RMR on metabolic health criteria except for the HOMA. Further studies are needed to investigate the effects of RMR on glucose abnormalities that may lead to modify cardio-metabolic criteria.

Low Resting Metabolic Rate in Exercise-Associated Amenorrhea is not Due to a Reduced Proportion of Energetically Expensive Tissue Compartments

BACKGROUND: Energy deficiency in exercising women is associated with menstrual disturbances and a concomitant reduction in resting metabolic rate (RMR) when expressed relative to body size or lean mass. It remains unknown whether this apparent RMR suppression is a consequence of a reduction in metabolically active tissue compartments during energy deficiency or due to metabolic adaptations at the tissue level. PURPOSE: To explore whether the reduced RMR in women with exercise-associated amenorrhea is explained by a lower proportion of energetically expensive tissue compartments or the result of metabolic adaptations. METHODS: RMR and metabolic tissue compartments were compared among exercising women with amenorrhea (AMEN, n=42) and eumenorrheic, ovulatory menstrual cycles (OV, n=37). RMR was measured using indirect calorimetry and predicted from metabolic tissue compartments as measured by dual-energy X-ray absorptiometry (DXA). RESULTS: Measured RMR was lower than DXA-predicted RMR in AMEN (1215±31 vs. 1327±18 kcal/d, p<0.001) but not in OV (1284±24 vs. 1252±17, p=0.16), resulting in a lower ratio of measured to DXA-predicted RMR in AMEN vs. OV (91±2% vs. 103±2%, p<0.001). Total triiodothyronine was also reduced in AMEN when compared with OV (80.1±3.4 vs. 92.4±2.1 ng/dL, p=0.003). Residual mass was greater (p<0.001) and adipose tissue was reduced (p=0.003) in AMEN when compared to OV. Brain, skeletal muscle, and bone mass were not different among groups. CONCLUSION: Our findings suggest that RMR suppression in exercise-associated amenorrhea is not the result of a reduced size of energetically expensive tissue compartments but due to metabolic adaptations at the tissue level that are indicative of energy conservation.

High respiratory quotient is associated with increases in body weight and fat mass in young adults.

Metabolic disturbances, such as reduced rates of fat oxidation (high respiratory quotient (RQ)) or low energy expenditure (low resting metabolic rate (RMR)), may contribute to obesity. The objective was to determine the association between a high RQ or a low RMR and changes in body weight and body composition over 1 year. We measured RQ and RMR in 341 adults using indirect calorimetry, along with body weight/body composition using dual-energy X-ray absorptiometery, energy expenditure using an arm-based activity monitor and energy intake using dietary recalls. Participants were classified into low, moderate or high RQ and RMR (adjusted for age, sex, race and body composition) groups according to tertiles by sex. Follow-up measurements were completed every 3 months. Individuals with a high RQ had larger gains in body weight and fat mass compared with individuals with a low/moderate RQ at month 3, and increases in fat mass were more than double among individuals with a high RQ at 12 months (1.3±3.0 vs 0.6±3.7 kg, P=0.03). Individuals with a low RMR did not gain more body weight nor fat mass compared with individuals with a moderate/high RMR. The primary finding is a high RQ is predictive of gains in body weight and fat mass over a 12-month period among young adults, with changes occurring as soon as 3 months. In addition, a low RMR was not associated with gains in body weight or fat mass over the same period.

Reduced Resting Metabolic Rate in Adults with Hemiparetic Chronic Stroke

ObjectiveResting metabolic rate (RMR) is the component of energy expenditure that explains the largest proportion of total daily energy requirements. Since RMR is determined largely by fat-free mass and a low RMR predicts weight gain in healthy adults, identifying the role of muscle atrophy following stroke on RMR may help identify ways to mitigate the development of obesity post-stroke.MethodsThirty-nine stroke survivors with chronic hemiparesis (mean ± SEM: age: 61 ± 1 years, latency from stroke: 107 ± 40 months, BMI: 31 ± 3 kg/m2) underwent DXA scans for measurement of body composition, including total, paretic, and non-paretic leg lean mass and fasted, 30-min indirect calorimetry for measurement of RMR.ResultPredicted RMR was calculated by the Mifflin-St Jeor equation, which considers weight, height, and age for both men and women. RMR was 14% lower than predicted (1438 ± 45 vs. 1669 ± 38 kcals/24 hrs; P<0.01). Total (r=0.73, P<0.01), paretic (r=0.72, P<0.01) and non-paretic (r=0.67, P<0.01) leg lean mass predicted RMR.ConclusionThese data indicate that muscle atrophy post stroke may lead to a reduced RMR. This substantiates the need to attenuate the loss of lean mass after a stroke to prevent declines in RMR and possible weight gain common post-stroke.

Resting and daily energy expenditures during reproduction are adjusted in opposite directions in free‐living birds

Summary Reproduction is energetically expensive, and daily energy expenditure (DEE) often peaks during the period of rearing young. The ‘potentiation’ hypothesis predicts that high DEE needs to be sustained by a corresponding up‐regulation of metabolic machinery; thus, a concomitant increase in the resting metabolic rate (RMR) is expected. Alternatively, the ‘compensation’ hypothesis predicts that DEE and RMR are regulated independently and animals may maintain low RMR to maximize the energy available for reproduction. This might particularly be the case if DEE was limited, for example, by extrinsic food supply or intrinsic physiological factors. We tested these hypotheses in free‐living seabirds by manipulating their energy demands (experimentally reduced or increased brood size) and supplies (providing supplemental food), and simultaneously measuring their DEE and RMR (by the doubly labelled water method and an indirect hormonal proxy, respectively). In support of the ‘compensation’ hypothesis, metabolic rates were adjusted independently and in opposite directions with an increase in DEE and a decrease in the hormonal proxy for RMR in individuals rearing young compared to birds with removed broods. Energy expenditure of unfed birds with chicks appeared to be limited as experimental brood enlargement did not cause an increase in DEE. Supplemental feeding did not allow DEE to exceed this apparent limitation. We propose that a reduction in the resting metabolism is a strategy to increase allocation of energy to reproduction when DEE is constrained and that this constraint is unlikely to be related to food supply.

Examining Variations of Resting Metabolic Rate of Adults

There has not been a recent comprehensive effort to examine existing studies on the resting metabolic rate (RMR) of adults to identify the effect of common population demographic and anthropometric characteristics. Thus, we reviewed the literature on RMR (kcal·kg(-1)·h(-1)) to determine the relationship of age, sex, and obesity status to RMR as compared with the commonly accepted value for the metabolic equivalent (MET; e.g., 1.0 kcal·kg(-1)·h(-1)). Using several databases, scientific articles published from 1980 to 2011 were identified that measured RMR, and from those, others dating back to 1920 were identified. One hundred and ninety-seven studies were identified, resulting in 397 publication estimates of RMR that could represent a population subgroup. Inverse variance weighting technique was applied to compute means and 95% confidence intervals (CI). The mean value for RMR was 0.863 kcal·kg(-1)·h(-1) (95% CI = 0.852-0.874), higher for men than women, decreasing with increasing age, and less in overweight than normal weight adults. Regardless of sex, adults with BMI ≥ 30 kg·m(-2) had the lowest RMR (<0.741 kcal·kg(-1)·h(-1)). No single value for RMR is appropriate for all adults. Adhering to the nearly universally accepted MET convention may lead to the overestimation of the RMR of approximately 10% for men and almost 15% for women and be as high as 20%-30% for some demographic and anthropometric combinations. These large errors raise questions about the longstanding adherence to the conventional MET value for RMR. Failure to recognize this discrepancy may result in important miscalculations of energy expended from interventions using physical activity for diabetes and other chronic disease prevention efforts.

Energy availability and the female athlete triad in elite endurance athletes.

The female athlete triad (Triad), links low energy availability (EA), with menstrual dysfunction (MD), and impaired bone health. The aims of this study were to examine associations between EA/MD and energy metabolism and the prevalence of Triad-associated conditions in endurance athletes. Forty women [26.2 ± 5.5 years, body mass index (BMI) 20.6 ± 2.0 kg/m(2), body fat 20.0 ± 3.0%], exercising 11.4 ± 4.5 h/week, were recruited from national teams and competitive clubs. Protocol included gynecological examination; assessment of bone health; indirect respiratory calorimetry; diet and exercise measured 7 days to assess EA; eating disorder (ED) examination; blood analysis. Subjects with low/reduced EA (< 45 kcal/kg FFM/day), had lower resting metabolic rate (RMR) compared with those with optimal EA [28.4 ± 2.0 kcal/kg fat-free mass (FFM)/day vs 30.5 ± 2.2 kcal/kg FFM/day, P < 0.01], as did subjects with MD compared with eumenorrheic subjects (28.6 ± 2.4 kcal/kg FFM/day vs 30.2 ± 1.8 kcal/kg FFM/day, P < 0.05). 63% had low/reduced EA, 25% ED, 60% MD, 45% impaired bone health, and 23% had all three Triad conditions. 53% had low RMR, 25% hypercholesterolemia, and 38% hypoglycemia. Conclusively, athletes with low/reduced EA and/or MD had lowered RMR. Triad-associated conditions were common in this group of athletes, despite a normal BMI range. The high prevalence of ED, MD, and impaired bone health emphasizes the importance of prevention, early detection, and treatment of energy deficiency.

“IDEAL” Aging Is Associated with Lower Resting Metabolic Rate: The Baltimore Longitudinal Study of Aging

To assess the associations among age, health status, and resting metabolic rate (RMR) in a large population of older adults. Cross-sectional analysis. Community-dwelling volunteers from the Baltimore Longitudinal Study of Aging (BLSA). Persons aged 40 to 96 (mean 68.2 ± 11.0) who underwent a comprehensive physical examination, cognitive assessment, RMR testing, body composition assessment, and physical function testing during a 3-day clinic visit (N = 420). Participants were assigned to Insight into the Determination of Exceptional Aging and Longevity (IDEAL) or non-IDEAL categories based on health status. IDEAL participants were defined according to the absence of physical and cognitive impairments, chronic conditions and comorbidities, and blood profile abnormalities. A three-stage linear regression model was used to assess the relationship between RMR and age, using IDEAL classification as a predictor and adjusting for sex and body composition. Resting metabolic rate averaged 1,512.4 ± 442.9 kcal/d and was lower with older age (β = -8.55, P < .001). After adjusting for age, sex, and body composition, RMR was 109.6 kcal/d lower in IDEAL than non-IDEAL participants (P < .005). Individuals who are fully functional and free of major medical conditions have lower RMR than those with disease and functional impairments. These findings suggest that health status plays a role in energy use and regulation independent of age and body composition and that elevated RMR may be a global biomarker of poor health in older persons.

Effect of dietary fatty acids on metabolic rate and nonshivering thermogenesis in golden hamsters

Hibernating rodents prior to winter tend to select food rich in polyunsaturated fatty acids (PUFA). Several studies found that such diet may positively affect their winter energy budget by enhancing torpor episodes. However, the effect of composition of dietary fatty acids (FA) on metabolism of normothermic heterotherms is poorly understood. Thus we tested whether diets different in FA composition affect metabolic rate (MR) and the capacity for nonshivering thermogenesis (NST) in normothermic golden hamsters (Mesocricetus auratus). Animals were housed in outdoor enclosures from May 2010 to April 2011 and fed a diet enriched with PUFA (i.e., standard food supplemented weekly with sunflower and flax seeds) or with saturated and monounsaturated fatty acids (SFA/MUFA, standard food supplemented with mealworms). Since diet rich in PUFA results in lower MR in hibernating animals, we predicted that PUFA-rich diet would have similar effect on MR of normothermic hamsters, that is, normothermic hamsters on the PUFA diet would have lower metabolic rate in cold and higher NST capacity than hamsters supplemented with SFA/MUFA. Indeed, in winter resting metabolic rate (RMR) below the lower critical temperature was higher and NST capacity was lower in SFA/MUFA-supplemented animals than in PUFA-supplemented ones. These results suggest that the increased capacity for NST in PUFA-supplemented hamsters enables them lower RMR below the lower critical temperature of the thermoneural zone.

Abstract P293: Resting Metabolic Rate, Cardiorespiratory Fitness, and Racial Differences in Adiposity among Adult Women

Background: African American (AA) adult females have a higher prevalence of overweight and obesity compared to their Caucasian (Cauc) peers. Lower resting metabolic rate (RMR) values, a hypothesized contributor to higher levels of adiposity, have been observed among AA women. However, it is unknown whether cardiorespiratory fitness (CRF) is associated with RMR in this population. Methods: Sixty-two overweight/obese (body mass index [BMI] ≥25.0) yet healthy women (42 Cauc, 20 AA) between the ages of 21-35 years were recruited for the present study. RMR was measured using a ventilated hood system. Participants arrived fasted for at least 12 hrs and having refrained from alcohol/exercise for at least 24 hrs. Participants rested in a supine position for 30-minutes, followed by a 30-minute RMR gas collection period. Body weight (BW) and height were measured and body fat (BF) was calculated as the percentage of total weight identified as fat tissue by dual x-ray absorptiometry. CRF was measured via a metabolic cart during a modified Bruce treadmill protocol. Total energy expenditure (TEE) was assessed using an arm-based physical activity monitor worn at all times for 10 consecutive days. Energy intake (EI) was assessed over a 14-day period via interviewer-administered dietary recall. Results: Cauc and AA participants were similar in terms of age (27.6±4.2 years), weight (79.9±9.9 kg), BMI (29.4±2.9 kg/m2), body fat percentage (41.0±5.1 percent), and EI (1760±397 kcal/day). Compared to Cauc, AA women were slightly shorter (162.4±7.0 vs. 165.8±5.1 cm, p=0.0371), lower CRF (27.4±3.8 vs. 31.4±5.2 ml/kg/min, p=0.0032), lower TEE (2438±264 vs. 2598±303 kcal/day, p=0.0102) and lower RMR (1436±222 vs. 1569±181 kcal/day, p=0.0154). Energy expenditure resulting from moderate/vigorous activity was higher in Cauc females (552±386 vs. 355±197 kcal/day, p=0.0102). RMR was correlated with fat mass, CRF and race. After adjustment for age, race, body weight, fat-free mass, fat mass, and CRF, the least squares means for RMR remained lower in AA compared to Cauc (1444 vs. 1565 kcal/day, p=0.0034) and was only significantly related race (p=0.0034). Conclusion: The results of this study confirm previous research reporting lower RMR values among AA females compared to their Cauc counterparts, though these differences did not result in variations of adiposity. The current analyses suggest CRF plays an important role in the determination of RMR. The differences among racial groups in energy expenditure resulting from moderate/vigorous activity may play a key role in the determination of CRF and ultimately RMR.

Resting metabolic rate is associated with hunger, self-determined meal size, and daily energy intake and may represent a marker for appetite

There are strong logical reasons why energy expended in metabolism should influence the energy acquired in food-intake behavior. However, the relation has never been established, and it is not known why certain people experience hunger in the presence of large amounts of body energy. We investigated the effect of the resting metabolic rate (RMR) on objective measures of whole-day food intake and hunger. We carried out a 12-wk intervention that involved 41 overweight and obese men and women [mean ± SD age: 43.1 ± 7.5 y; BMI (in kg/m(2)): 30.7 ± 3.9] who were tested under conditions of physical activity (sedentary or active) and dietary energy density (17 or 10 kJ/g). RMR, daily energy intake, meal size, and hunger were assessed within the same day and across each condition. We obtained evidence that RMR is correlated with meal size and daily energy intake in overweight and obese individuals. Participants with high RMRs showed increased levels of hunger across the day (P < 0.0001) and greater food intake (P < 0.00001) than did individuals with lower RMRs. These effects were independent of sex and food energy density. The change in RMR was also related to energy intake (P < 0.0001). We propose that RMR (largely determined by fat-free mass) may be a marker of energy intake and could represent a physiologic signal for hunger. These results may have implications for additional research possibilities in appetite, energy homeostasis, and obesity. This trial was registered under international standard identification for controlled trials as ISRCTN47291569.

Personality and the pace‐of‐life syndrome: variation and selection on exploration, metabolism and locomotor performances

Summary Consistent individual differences in behaviour are seen in numerous animals and could be maintained by life‐history trade‐offs and integrated within a pace‐of‐life syndrome involving physiological and locomotor traits. Lizard species are characterized by inter‐specific variation in activity and foraging behaviours associated with differences in locomotor performances and metabolic rates. Similar syndromes could exist within species, but have not been investigated so far. We scored the exploratory behaviour of newborn common lizards (Zootoca vivipara) using a neutral arena test and measured concomitantly resting metabolic rate (RMR), maximal sprint speed (MSS) and endurance capacity. Animals were released in outdoor enclosures exposed to avian predation and measured again for the same traits 1 year later. Common lizards displayed consistent individual differences over a week for an exploration score associated with high activity in the neutral arena. Individual differences in three activity scores were also consistent over the first year of life. Correlations among behavioural, metabolic and locomotor traits were weak, except for a marginally significant, positive correlation between exploration score and MSS and endurance at the age of 1 year. Correlational survival selection was found for RMR and exploration score such that newborns with low exploration score and high RMR and newborns with high exploration score and low RMR survived better. Correlational growth selection was also found with faster growth in newborns with low exploration score and high RMR. The results are discussed against recent hypotheses to explain the maintenance of animal temperaments.

Effects of Fluid Load on Human Urine Characteristics Related to Workplace Drug Testing *

During workplace drug testing, urine is tested for dilution, substitution and adulteration. Donors argue that these findings are due to medical, health or working conditions or diet and genetic differences. There is a paucity of data correlating changes in urine characteristics after a fluid load to various body parameters. Therefore, five urine specimens (one in the morning, one prior to drinking 800 mL of a beverage, and three time intervals thereafter) from 12 males and 12 females were tested for four different beverages on separate occasions. Of the 480 samples, 376 were in sufficient amounts. Of these 376, 36 (10%) had creatinine <20 mg/dL but ≥2 mg/dL; 27 (75%) of 36 had specific gravity <1.0030 but >1.0010. Thus, these 27 samples can be considered to be dilute; 20 (74%) of 27 were from females. For males with at least one dilute sample, body fat was 11% less and resting metabolic rate (RMR) was 29% more than males with no dilute samples (p > 0.05); for females with at least one dilute sample, height was 8% less and weight 20% less than females with no dilute samples (p > 0.05). Individuals with a higher RMR appear to have a greater potential for producing dilute urine specimens than those with a lower RMR. Thus, a dilute sample does not necessarily indicate that it was intentionally diluted. Such samples must be carefully evaluated in consideration with recent consumption of liquid by donors to avoid false accusations.