Adults with metabolically healthy overweight or obesity present more brown adipose tissue and higher thermogenesis than their metabolically unhealthy counterparts

BACKGROUND

There is a subset of individuals with overweight/obesity characterized by a lower risk of cardiometabolic complications, the so-called metabolically healthy overweight/obesity (MHOO) phenotype. Despite the relatively higher levels of subcutaneous adipose tissue and lower visceral adipose tissue observed in individuals with MHOO than individuals with metabolically unhealthy overweight/obesity (MUOO), little is known about the differences in brown adipose tissue (BAT).

METHODS

This study included 53 young adults (28 women) with a body mass index (BMI) ≥25 kg/m2 which were classified as MHOO (n = 34) or MUOO (n = 19). BAT was assessed through a static 18F-FDG positron emission tomography/computed tomography scan after a 2-h personalized cooling protocol. Energy expenditure, skin temperature, and thermal perception were assessed during a standardized mixed meal test (3.5 h) and a 1-h personalized cold exposure. Body composition was assessed by dual-energy x-ray absorptiometry, energy intake was determined during an ad libitum meal test and dietary recalls, and physical activity levels were determined by a wrist-worn accelerometer.

FINDINGS

Participants with MHOO presented higher BAT volume (+124%, P = 0.008), SUVmean (+63%, P = 0.001), and SUVpeak (+133%, P = 0.003) than MUOO, despite having similar BAT mean radiodensity (P = 0.354). In addition, individuals with MHOO exhibited marginally higher meal-induced thermogenesis (P = 0.096) and cold-induced thermogenesis (+158%, P = 0.050). Moreover, MHOO participants showed higher supraclavicular skin temperature than MUOO during the first hour of the postprandial period and during the cold exposure, while no statistically significant differences were observed in other skin temperature parameters. We observed no statistically significant differences between MHOO and MUOO in thermal perception, body composition, outdoor ambient temperature exposure, resting metabolic rate, energy intake, or physical activity levels.

INTERPRETATION

Adults with MHOO present higher BAT volume and activity than MUOO. The higher meal- and cold-induced thermogenesis and cold-induced supraclavicular skin temperature are compatible with a higher BAT activity. Overall, these results suggest that BAT presence and activity might be linked to a healthier phenotype in young adults with overweight or obesity.

FUNDING

See acknowledgments section.

Effect of Moderate Versus Vigorous Exercise Intensity on Body Composition in Young Untrained Adults: The Activating Brown Adipose Tissue Through Exercise (ACTIBATE) Randomized Controlled Trial

The present study aimed to investigate the effect of a 24-week aerobic + resistance training programs at moderate versus vigorous intensity on body composition, and the persistence of the changes after a 10-month free-living period, in young untrained adults. This report is based on a secondary analysis from the activating brown adipose tissue through exercise (ACTIBATE) single-center unblinded randomized controlled trial. A total of 144 young adults (65.6% women) aged 18-25 years were randomly allocated to three different groups: (a) aerobic + resistance exercise training program based on the international physical activity recommendations at vigorous intensity (Ex-Vigorous group), (b) at moderate intensity (Ex-Moderate group), and (c) control group (no exercise). Body composition outcomes were determined by a dual-energy X-ray absorptiometry scanner. Both Ex-Vigorous and Ex-Moderate decreased body weight, fat mass, and visceral adipose tissue mass in a similar manner (all p < .04). After a 10-month free-living period, these parameters returned to baseline levels in both exercise groups (all ps < .03). No differences between the exercise groups and the control group were noted in lean mass changes (all ps > .1). A 24-week aerobic + resistance training intervention based on the international physical activity recommendations was enough to improve body weight, fat mass, and visceral adipose tissue mass in untrained young adults, independently of the exercise intensity (moderate vs. vigorous).

Effect of a 24-Week Concurrent Exercise Intervention on Neck Adiposity and Its Distribution in Young Adults: The ACTIBATE Randomized Controlled Trial

Neck adipose tissue (NAT) accumulation and neck circumference are independent predictors of cardiometabolic risk (CMR) and low-grade chronic inflammation in young adults. The present study examines whether a 24-week concurrent exercise intervention can reduce NAT volume and neck circumference in young adults, and whether any changes in these variables are related to changes in body composition, CMR, and the inflammatory profile. Seventy-four participants (51 women, age 22 ± 2 years) were included in the main analyses, after being randomly assigned to either a (a) control (n = 34), (b) moderate-intensity exercise (n = 19), or (c) vigorous-intensity exercise (n = 21) group. Participants in the exercise groups trained 3-4 days/week (endurance + resistance exercise training). NAT volume and NAT distribution across different depots were estimated using computed tomography before and after the intervention. Anthropometric variables, body composition (determined by dual-energy X-ray absorptiometry), and CMR/inflammatory markers were also recorded. The exercise intervention did not reduce the total NAT volume, nor was NAT distribution affected (p > .05). However, it did reduce neck circumference in the vigorous-intensity exercise group compared with the moderate-intensity exercise and control groups (by 0.8 and 1 cm, respectively, p ≤ .05). Changes in total NAT and neck circumference were positively, albeit weakly, related (adj. R2: .05-.21, all p ≤ .05) to changes in body weight and adiposity, leptin (only total NAT), and CMR (only neck circumference). Altogether 24 weeks of concurrent exercise does not appear to reduce NAT accumulation in young adults, but may slightly reduce neck circumference in those who partake in vigorous exercise.

Association of meal timing with body composition and cardiometabolic risk factors in young adults

PURPOSE

To investigate the association of meal timing with body composition and cardiometabolic risk factors in young adults.

METHODS

In this cross-sectional study participated 118 young adults (82 women; 22 ± 2 years old; BMI: 25.1 ± 4.6 kg/m²). Meal timing was determined via three non-consecutive 24-h dietary recalls. Sleep outcomes were objectively assessed using accelerometry. The eating window (time between first and last caloric intake), caloric midpoint (local time at which ≥ 50% of daily calories are consumed), eating jetlag (variability of the eating midpoint between non-working and working days), time from the midsleep point to first food intake, and time from last food intake to midsleep point were calculated. Body composition was determined by DXA. Blood pressure and fasting cardiometabolic risk factors (i.e., triglycerides, total cholesterol, high-density lipoprotein-cholesterol, low-density lipoprotein-cholesterol, and insulin resistance) were measured.

RESULTS

Meal timing was not associated with body composition (p > 0.05). The eating window was negatively related to HOMA-IR and cardiometabolic risk score in men (R² = 0.348, β = - 0.605; R² = 0.234, β = - 0.508; all p ≤ 0.003). The time from midsleep point to first food intake was positively related to HOMA-IR and cardiometabolic risk score in men (R² = 0.212, β = 0.485; R² = 0.228, β = 0.502; all p = 0.003). These associations remained after adjusting for confounders and multiplicity (all p ≤ 0.011).

CONCLUSIONS

Meal timing seems unrelated to body composition in young adults. However, a longer daily eating window and a shorter time from midsleep point to first food intake (i.e., earlier first food intake in a 24 h cycle) are associated with better cardiometabolic health in young men.

CLINICAL TRIAL REGISTRATION

NCT02365129 ( https://www.

CLINICALTRIALS

gov/ct2/show/NCT02365129?term=ACTIBATE&draw=2&rank=1 ).

Fecal microbiota composition is related to brown adipose tissue 18F-fluorodeoxyglucose uptake in young adults

OBJECTIVE

Human brown adipose tissue (BAT) has gained considerable attention as a potential therapeutic target for obesity and its related cardiometabolic diseases; however, whether the gut microbiota might be an efficient stimulus to activate BAT metabolism remains to be ascertained. We aimed to investigate the association of fecal microbiota composition with BAT volume and activity and mean radiodensity in young adults.

METHODS

82 young adults (58 women, 21.8 ± 2.2 years old) participated in this cross-sectional study. DNA was extracted from fecal samples and 16S rRNA sequencing was performed to analyse the fecal microbiota composition. BAT was determined via a static ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography-computed tomography scan (PET/CT) after a 2 h personalized cooling protocol. ¹⁸F-FDG uptake was also quantified in white adipose tissue (WAT) and skeletal muscles.

RESULTS

The relative abundance of Akkermansia, Lachnospiraceae sp. and Ruminococcus genera was negatively correlated with BAT volume, BAT SUVmean and BAT SUVpeak (all rho ≤ - 0.232, P ≤ 0.027), whereas the relative abundance of Bifidobacterium genus was positively correlated with BAT SUVmean and BAT SUVpeak (all rho ≥ 0.262, P ≤ 0.012). On the other hand, the relative abundance of Sutterellaceae and Bifidobacteriaceae families was positively correlated with ¹⁸F-FDG uptake by WAT and skeletal muscles (all rho ≥ 0.213, P ≤ 0.042). All the analyses were adjusted for the PET/CT scan date as a proxy of seasonality.

CONCLUSION

Our results suggest that fecal microbiota composition is involved in the regulation of BAT and glucose uptake by other tissues in young adults. Further studies are needed to confirm these findings.

CLINICAL TRIAL INFORMATION

ClinicalTrials.gov no. NCT02365129 (registered 18 February 2015).

Nef enhances HIV-1 replication and infectivity independently of SERINC5 in CEM T cells

A primary function of HIV-1 Nef is the enhancement of viral infectivity and replication. Whether counteraction of the antiretroviral proteins SERINC3 and SERINC5 is the cause of this positive influence on viral growth-rate and infectivity remains unclear. Here, we utilized CRISPR/Cas9 to knockout SERINC3 and SERINC5 in a leukemic CD4-positive T cell line (CEM) that displays nef-related infectivity and growth-rate phenotypes. Viral replication was attenuated in CEM cells infected with HIV-1 lacking Nef (HIV-1ΔNef). This attenuated growth-rate phenotype was observed regardless of whether the coding regions of the serinc3 or serinc5 genes were intact. Moreover, knockout of serinc5 alone or of both serinc5 and serinc3 together failed to restore the infectivity of HIV1ΔNef virions produced from infected CEM cells. Our results corroborate a similar study using another T-lymphoid cell line (MOLT-3) and indicate that the antagonism of SERINC3 and SERINC5 does not fully explain the virology of HIV-1 lacking Nef.

Dihydrocapsiate does not increase energy expenditure nor fat oxidation during aerobic exercise in men with overweight/obesity: a randomized, triple-blinded, placebo-controlled, crossover trial

Background

Prior evidence suggests that capsinoids ingestion may increase resting energy expenditure (EE) and fat oxidation (FATox), yet whether they can modulate those parameters during exercise conditions remains poorly understood. We hypothesized that dihydrocapsiate (DHC) ingestion would increase EE and specifically FATox during an acute bout of aerobic exercise at FATmax intensity (the intensity that elicits maximal fat oxidation during exercise [MFO]) in men with overweight/obesity. Since FATmax and MFO during aerobic exercise appear to be indicators of metabolic flexibility, whether DHC has an impact on FATox in this type of population is of clinical interest.

Methods

A total of 24 sedentary men (age = 40.2 ± 9.2 years-old; body mass index = 31.6 ± 4.5 kg/m² [n = 11 overweight, n = 13 obese]) participated in this randomized, triple-blinded, placebo-controlled, crossover trial (registered under ClinicalTrials.gov Identifier no. NCT05156697). On the first day, participants underwent a submaximal exercise test on a cycle ergometer to determine their MFO and FATmax intensity during exercise. After 72 hours had elapsed, the participants returned on 2 further days (≥ 72 hours apart) and performed a 60 min steady-state exercise bout (i.e. cycling at their FATmax, constant intensity) after ingesting either 12 mg of DHC or placebo; these conditions were randomized. Respiratory gas exchange was monitored by indirect calorimetry. Serum marker concentrations (i.e. glucose, triglycerides, non-esterified fatty acids (NEFAs), skin temperature, thermal perception, heart rate, and perceived fatigue) were assessed.

Results

There were no significant differences (P > 0.05) between DHC and placebo conditions in the EE and FATox during exercise. Similarly, no significant changes were observed in glucose, triglycerides, or NEFAs serum levels, neither in the skin temperature nor thermal perception across conditions. Heart rate and perceived fatigue did not differ between conditions.

Conclusions

DHC supplementation does not affect energy metabolism during exercise in men with overweight/obesity.

No evidence of brown adipose tissue activation after 24 weeks of supervised exercise training in young sedentary adults in the ACTIBATE randomized controlled trial

Exercise modulates both brown adipose tissue (BAT) metabolism and white adipose tissue (WAT) browning in murine models. Whether this is true in humans, however, has remained unknown. An unblinded randomized controlled trial (ClinicalTrials.gov ID: NCT02365129) was therefore conducted to study the effects of a 24-week supervised exercise intervention, combining endurance and resistance training, on BAT volume and activity (primary outcome). The study was carried out in the Sport and Health University Research Institute and the Virgen de las Nieves University Hospital of the University of Granada (Spain). One hundred and forty-five young sedentary adults were assigned to either (i) a control group (no exercise, n = 54), (ii) a moderate intensity exercise group (MOD-EX, n = 48), or (iii) a vigorous intensity exercise group (VIG-EX n = 43) by unrestricted randomization. No relevant adverse events were recorded. 97 participants (34 men, 63 women) were included in the final analysis (Control; n = 35, MOD-EX; n = 31, and VIG-EX; n = 31). We observed no changes in BAT volume (Δ Control: −22.2 ± 52.6 ml; Δ MOD-EX: −15.5 ± 62.1 ml, Δ VIG-EX: −6.8 ± 66.4 ml; P = 0.771) or ¹⁸F-fluorodeoxyglucose uptake (SUVpeak Δ Control: −2.6 ± 3.1 ml; Δ MOD-EX: −1.2 ± 4.8, Δ VIG-EX: −2.2 ± 5.1; p = 0.476) in either the control or the exercise groups. Thus, we did not find any evidence of an exercise-induced change on BAT volume or activity in young sedentary adults.

Exercise modulates brown adipose tissue (BAT) metabolism in murine models. Here the authors report that there is no evidence that 24 weeks of supervised exercise training modulates BAT volume or function in young sedentary adults in the ACTIBATE randomized controlled trial.

A larger brown fat volume and lower radiodensity are related to a greater cardiometabolic risk, especially in young men

OBJECTIVES

Brown adipose tissue (BAT) is important in the maintenance of cardiometabolic health in rodents. Recent reports appear to suggest the same in humans, although if this is true remains elusive partly because of the methodological bias that affected previous research. This cross-sectional work reports the relationships of cold-induced BAT volume, activity (peak standardized uptake, SUVpeak), and mean radiodensity (an inverse proxy of the triacylglycerols content) with the cardiometabolic and inflammatory profile of 131 young adults, and how these relationships are influenced by sex and body weight.

DESIGN

This is a cross-sectional study.

METHODS

Subjects underwent personalized cold exposure for 2 h to activate BAT, followed by static 18F-fluorodeoxyglucose PET-CT scanning to determine BAT variables. Information on cardiometabolic risk (CMR) and inflammatory markers was gathered, and a CMR score and fatty liver index (FLI) were calculated.

RESULTS

In men, BAT volume was positively related to homocysteine and liver damage markers concentrations (independently of BMI and seasonality) and the FLI (all P ≤ 0.05). In men, BAT mean radiodensity was negatively related to the glucose and insulin concentrations, alanine aminotransferase activity, insulin resistance, total cholesterol/HDL-C, LDL-C/HDL-C, the CMR score, and the FLI (all P ≤ 0.02). In women, it was only negatively related to the FLI (P < 0.001). These associations were driven by the results for the overweight and obese subjects. No relationship was seen between BAT and inflammatory markers (P > 0.05).

CONCLUSIONS

A larger BAT volume and a lower BAT mean radiodensity are related to a higher CMR, especially in young men, which may support that BAT acts as a compensatory organ in states of metabolic disruption.

Plasma Levels of Endocannabinoids and Their Analogues Are Related to Specific Fecal Bacterial Genera in Young Adults: Role in Gut Barrier Integrity

OBJECTIVE

To investigate the association of plasma levels of endocannabinoids with fecal microbiota.

METHODS

Plasma levels of endocannabinoids, anandamide (AEA) and 2-arachidonoylglycerol (2-AG), as well as their eleven analogues, and arachidonic acid (AA), were measured using liquid chromatography-tandem mass spectrometry in 92 young adults. DNA extracted from stool samples was analyzed using 16S rRNA gene sequencing. Lipopolysaccharide levels were measured in plasma samples.

RESULTS

Plasma levels of endocannabinoids and their analogues were not related to beta or alpha diversity indexes. Plasma levels of AEA and related N-acylethanolamines correlated positively with the relative abundance of Faecalibacterium genus (all rho ≥ 0.26, p ≤ 0.012) and Akkermansia genus (all rho ≥ 0.22, p ≤ 0.036), and negatively with the relative abundance of Bilophila genus (all rho ≤ -0.23, p ≤ 0.031). Moreover, plasma levels of 2-AG and other acylglycerols correlated positively with the relative abundance of Parasutterella (all rho ≥ 0.24, p ≤ 0.020) and Odoribacter genera (all rho ≥ 0.27, p ≤ 0.011), and negatively with the relative abundance of Prevotella genus (all rho ≤ -0.24, p ≤ 0.023). In participants with high lipopolysaccharide values, the plasma levels of AEA and related N-acylethanolamines, as well as AA and 2-AG, were negatively correlated with plasma levels of lipopolysaccharide (all rho ≤ -0.24, p ≤ 0.020).

CONCLUSION

Plasma levels of endocannabinoids and their analogues are correlated to specific fecal bacterial genera involved in maintaining gut barrier integrity in young adults. This suggests that plasma levels of endocannabinoids and their analogues may play a role in the gut barrier integrity in young adults.

Thermogenic responses to different clamped skin temperatures in cold-exposed men and women

Despite many decades of research examining thermoregulatory responses under varying cold stresses in humans, very little is known about the variability in metabolic heat production and shivering activity. Here, we used a novel closed-loop mean skin temperature clamping technique with a liquid-conditioned suit to isolate the effects of mean skin temperature on the subjective evaluation of thermal sensation, heat production, shivering responses, and oxidative fuel selection in young, lean and healthy men (n = 12) and women (n = 12). Our results showed a skin temperature-dependent increase in metabolic heat production (5.2±1.0 kJ/min, 5.9±1.0 kJ/min and 7.0±1.0 kJ/min with skin temperature maintained at 31°C, 29°C and 27°C, respectively; P< 0.0001) and shivering intensity in both men and women (0.6±0.1 %MVC, 1.1±0.4 %MVC and 2.5±0.7 %MVC, respectively; P<0.0001), including sex-dependent differences in heat production at all three temperatures (P < 0.005). Even when controlling for lean body mass and fat mass, sex differences persisted (P = 0.048 and P = 0.004, respectively), whereas controlling for differences in body surface area eliminated these differences. Interestingly, there were no sex differences in the cold-induced change in thermogenesis. Despite clamping skin temperature, there was tremendous variability in the rate of heat production and shivering intensity. Collectively this data suggests that many of the inter-individual differences in thermogenesis and shivering may be explained by differences in morphology and body composition.

Circulating concentrations of free triiodothyronine are associated with central adiposity and cardiometabolic risk factors in young euthyroid adults

Thyroid dysfunction is associated with classic cardiometabolic risk factors in humans. However, this relationship remains unclear in young euthyroid adults. The present work examines the associations of circulating thyroid hormones (THs) and thyroid-stimulating hormone (TSH) concentrations with body composition and cardiometabolic risk factors in young euthyroid adults. A total of 106 sedentary, euthyroid adults (72 women; 22 ± 2 years old) participated in this cross-sectional study. THs and TSH serum concentrations were determined in fasting conditions (6 h). Body composition (fat mass (FM), lean mass (LM), and visceral adipose tissue (VAT)) was determined by dual-energy X-ray absorptiometry, anthropometric parameters (weight, height, and waist circumference) were measured, and neck adipose tissue mass was quantified through computed tomography (CT) scanning. Cardiometabolic risk factors including fasting glucose and lipid metabolism markers, hepatic phosphatase and transaminases, and blood pressure were also assessed. Free triiodothyronine (FT3) concentration was positively associated with body mass index, LM, VAT, and waist circumference (all P ≤ 0.038). FT3 was also associated with glucose, insulin, HOMA-IR, fatty liver index, and blood pressure (all P < 0.024). All the associations were attenuated when adjusting for sex. In contrast, we found no associations of TSH or free thyroxine with any body composition parameter or cardiometabolic risk factors. In conclusion, FT3 is associated with central adiposity and cardiometabolic risk factors including insulin resistance, fatty liver index, and mean, systolic and diastolic blood pressure in young euthyroid adults. ClinicalTrials.gov identifier: NCT02365129.

Exercise-induced changes on exerkines that might influence brown adipose tissue metabolism in young sedentary adults

In rodents, exercise alters the plasma concentration of exerkines that regulate white adipose tissue (WAT) browning or brown adipose tissue (BAT) metabolism. This study aims to analyse the acute and chronic effect of exercise on the circulating concentrations of 16 of these exerkines in humans. Ten young sedentary adults (6 female) performed a maximum walking effort test and a resistance exercise session. The plasma concentration of 16 exerkines was assessed before, and 3, 30, 60, and 120 minutes after exercise. Those exerkines modified by exercise were additionally measured in another 28 subjects (22 women). We also measured the plasma concentrations of the exerkines before and after a 24-week exercise program (endurance + resistance; 3-groups: control, moderate-intensity and vigorous-intensity) in 110 subjects (75 women). Endurance exercise acutely increased the plasma concentration of lactate, norepinephrine, brain-derived neurotrophic factor, interleukin 6, and follistatin-like protein 1 (3 minutes after exercise), and musclin and fibroblast growth factor 21 (30 and 60 minutes after exercise), decreasing the plasma concentration of leptin (30 minutes after exercise). Adiponectin, atrial natriuretic peptide (ANP), β-aminoisobutyric acid, meteorin-like, follistatin, pro-ANP, irisin and myostatin were not modified or not detectable. The resistance exercise session increased the plasma concentration of lactate 3 minutes after exercise. Chronic exercise did not alter the plasma concentration of these exerkines. In sedentary young adults, acute endurance exercise releases to the bloodstream exerkines that regulate BAT metabolism and WAT browning. In contrast, neither a low-volume resistance exercise session nor a 24-week training program modified plasma levels of these molecules.Trial registration: ClinicalTrials.gov identifier: NCT02365129..

Brown Adipose Tissue Volume and Fat Content Are Positively Associated With Whole-Body Adiposity in Young Men-Not in Women

Human brown adipose tissue (BAT) volume has consistently been claimed to be inversely associated with whole-body adiposity. However, recent advances in the assessment of human BAT suggest that previously reported associations may have been biased. The present cross-sectional study investigates the association of BAT volume, mean radiodensity, and 18F-fluorodeoxyglucose (18F-FDG) uptake (assessed via a static positron emission tomography [PET]-computed tomography [CT] scan after a 2-h personalized cold exposure) with whole-body adiposity (measured by DXA) in 126 young adults (42 men and 84 women; mean ± SD BMI 24.9 ± 4.7 kg/m2). BAT volume, but not 18F-FDG uptake, was positively associated with BMI, fat mass, and visceral adipose tissue (VAT) mass in men but not in women. These associations were independent of the date when the PET-CT was performed, insulin sensitivity, and body surface area. BAT mean radiodensity, an inverse proxy of BAT fat content, was negatively associated with BMI, fat mass, and VAT mass in men and in women. These results refute the widely held belief that human BAT volume is reduced in obese persons, at least in young adults, and suggest that it might even be the opposite in young men.

Feasibility of Three Different 8h Time-Restricted Eating Schedules Over 4 Weeks in Spanish Adults With Overweight/Obesity: A Pilot Randomized Controlled Trial

Objectives

To investigate the feasibility and acceptability of three different 8h time-restricted eating (TRE) schedules (i.e., early TRE, late TRE, and self-selected TRE) over 4 weeks in adults with overweight/obesity from southern Spain.

Methods

A total of 22 adults with overweight/obesity and a baseline eating window ≥12h (13 women; 48 ± 10 years old; body mass index: 32.7 ± 5.8 kg/m2) were randomly assigned to one of the three 8h-TRE schedules: early TRE (first meal within the first 2h after waking up), late TRE (first meal 5–7h after waking up), and self-selected TRE (self-selected eating window). Feasibility and acceptability were assessed by adherence to the intervention, adverse events and validated questionnaires to assess sleep quality, depression, and anxiety.

Results

All participants completed the intervention. Adherence remained ≥95% in the late and self-selected TRE groups during the intervention, whereas it decreased from 94% (first week) to 68% (fourth week) in the early TRE group. Total adherence was not associated with baseline eating window (P = 0.644). The mean intervention eating window was 7.9 ± 0.5h, 7.1 ± 0.5h, and 7.4 ± 0.5h for the early, late, and self-selected TRE, respectively. Differences were noted between early and late TRE groups (P = 0.019). No serious adverse events were reported and no differences were observed in headache, nausea, acidity, diarrhea, thirstiness, hunger, cravings, tiredness, stress, irritability, and anxiety eating among TRE groups. After the intervention, the early TRE improved depression using two different validated questionnaires (P = 0.007 and P = 0.018), although no differences were observed across TRE groups (P = 0.863 and P = 0.197). A trend to significant improvement in sleep quality (P = 0.067) was observed in the early TRE group after the intervention, albeit no differences were noticed across TRE groups (P = 0.277).

Conclusions

These results suggest that early TRE may have lower feasibility and acceptability than late and self-selected TRE in adults with overweight/obesity from southern Spain. However, early TRE appears to enhance depression and sleep quality. Lastly, no serious adverse events were noted; hence, TRE seems a safe nutrition.

Funding Sources

N/A.

Heart rate rather than heart rate variability is better associated with cardiorespiratory fitness in adults

This study aimed to examine the association of heart rate (HR) and heart rate variability (HRV) with cardiorespiratory fitness (CRF) in adults. This cross-sectional study included 204 participants: 132 young adults (67% women; 22.3 ± 2.3 years) and 72 middle-aged adults (53% women; 53.2 ± 5 years). HR and HRV were measured using a Polar RS800CX heart rate monitor. CRF was assessed using a metabolic cart during an incremental test. HR was negatively associated with CRF relative to body weight (BW) in young adults adjusting for sex, age, and physical activity (β ranged from -0.200 to -0.195; all P ≤ 0.022). These associations disappeared after including fat mass as a covariate (all P ≥ 0.106) while remained significant after adjusting for fat-free mass (FFM; all P ≤ 0.008). Neither HR nor HRV variables were associated with CRF expressed as absolute values or relative to FFM in young and middle-aged adults after adjusting for the abovementioned covariates (all P ≥ 0.074). Our results suggest that HR rather than HRV is better associated with CRF relative to BW in young adults. However, this association seems to be explained by the inclusion of fat mass in the calculation of CRF relative to BW.Highlights Heart rate and heart rate variability variables have been associated with cardiorespiratory fitness.Our present results, and previous literature, suggest that the "simple" measurement of the heart rate could be easier to obtain and interpret than the heart rate variability variables.The heart rate variable rather than the heart rate variability variables is better associated with cardiorespiratory fitness relative to body weight in healthy young adults.

Impact of an intermittent and localized cooling intervention on skin temperature, sleep quality and energy expenditure in free-living, young, healthy adults

Where people live and work together it is not always possible to modify the ambient temperature; ways must therefore be found that allow individuals to feel thermally comfortable in such settings. The Embr Wave® is a wrist-worn device marketed as a 'personal thermostat' that can apply a local cooling stimulus to the skin. The aim of the present study was to determine the effect of an intermittent mild cold stimulus of 25 °C for 15-20 s every 5 min over 3.5 days under free-living conditions on 1) skin temperature, 2) perception of skin temperature, 3) sleep quality and 4) resting energy expenditure (REE) in young, healthy adults. Ten subjects wore the device for 3.5 consecutive days. This intervention reduced distal skin temperature after correcting for personal ambient temperature (P < 0.05), but did not affect the subjects' the perception of skin temperature, sleep quality or REE (all P ≥ 0.051). Thus, this intermittent mild cold regime can reduce distal skin temperature, and wearing it under free-living conditions for 3.5 days does not seem to impair the perception of skin temperature and sleep quality or modify REE.

Eating Behavior, Physical Activity and Exercise Training: A Randomized Controlled Trial in Young Healthy Adults

Regular physical activity (PA) is an important part of the treatment of several medical conditions, including overweight and obesity, in which there may be a weakened appetite control. Eating behaviour traits influence weight control and may be different in active and sedentary subjects. This paper reports the relationships between the time spent in sedentary behaviour and physical activity (PA) of different intensity, and eating behaviour traits in young, healthy adults. Additionally, it reports the results of a six-month-long, randomized, controlled trial to examine the effect of an exercise intervention on eating behaviour traits. A total of 139 young (22.06 ± 2.26 years) healthy adults (68.35% women) with a Body Mass Index (BMI) of 24.95 ± 4.57 kg/m² were enrolled. Baseline assessments of habitual PA were made using wrist-worn triaxial accelerometers; eating behaviour traits were examined via the self-reported questionnaires: Binge Eating, Three-Factor Eating Questionnaire-R18 and Control of Eating Questionnaire. The subjects were then randomly assigned to one of three groups: control (usual lifestyle), moderate-intensity exercise (aerobic and resistance training 3¨C4 days/week at a heart rate equivalent to 60% of the heart rate reserve (HRres) for the aerobic component, and at 50% of the 1 repetition maximum (RM) for the resistance component), or vigorous-intensity exercise (the same training but at 80% HRres for half of the aerobic training, and 70% RM for the resistance training). At baseline, sedentary behaviour was inversely associated with binge eating (r = −0.181, p < 0.05) and with uncontrolled eating (r = −0.286, p = 0.001). Moderate PA (MPA) was inversely associated with craving control (r = −0.188, p < 0.05). Moderate-to-vigorous PA (MVPA) was directly associated with binge eating (r = 0.302, p < 0.001) and uncontrolled eating (r = 0.346, p < 0.001), and inversely associated with craving control (r = −0.170, p < 0.015). Overall, PA was directly associated with binge eating (r = 0.275, p = 0.001), uncontrolled eating (r = 0.321, p < 0.001) and emotional eating (r = 0.204, p < 0.05). Additionally, only emotional eating was modified by the intervention, increasing in the vigorous-intensity exercise group (p < 0.05). In summary, we observed that time spent in sedentary behaviour/PA of different intensity is associated with eating behaviour traits, especially binge eating in young adults. In contrast, the six-month exercise intervention did not lead to appreciable changes in eating behaviour traits.

Neck adipose tissue accumulation is associated with higher overall and central adiposity, a higher cardiometabolic risk, and a pro-inflammatory profile in young adults

OBJECTIVES

Neck adipose tissue (NAT) volume increases with general adiposity, with fat accumulating in different neck tissue compartments. In patients with certain malignant/benign tumours, the accumulation of NAT, and certain NAT distributions, have been associated with cardiometabolic risk (CMR). However, it is unknown whether the same relationships exist in healthy people, and whether NAT accumulation and distribution are related to the inflammatory status.

METHODS

In this cross-sectional study, 139 young healthy adults (68% women) underwent a computed tomography scan to quantify the volume of compartmental (i.e., subcutaneous, intermuscular and perivertebral) and total NAT at the height of vertebra C5. Anthropometric indicators were measured, and body composition determined using dual energy X-ray absorptiometry. Information on CMR factors (i.e., blood glycaemic and lipid markers, blood pressure and physical fitness) was also gathered, and a CMR score calculated. Several plasma cytokines and serum components of the innate immune system were measured to determine the inflammatory status.

RESULTS

Compartmental and total NAT volumes were directly related to body mass index (BMI), and lean, fat, and visceral adipose tissue (VAT) masses (all, P ≤ 0.05). Larger compartmental (especially intermuscular) and total NAT volumes were directly associated with the CMR score, several CMR factors (i.e., glycaemic and lipid markers and blood pressure), and the C3, C4 and leptin concentrations. They were, however, inversely correlated with the CMR factors high density lipoprotein-cholesterol (HDL-C) and physical fitness, and with the adiponectin concentration (all P ≤ 0.05). Several of these associations remained statistically significant (P ≤ 0.05) after adjustment for BMI, body fat percentage or VAT mass. Overall, results did not change after applying false discovery rate correction.

CONCLUSIONS

NAT volume and its distribution among different tissue compartments is associated with the CMR and inflammatory profile of young healthy adults. Total NAT volume appears to be as valuable as VAT mass in terms of predicting CMR and inflammatory status.

Energy Expenditure and Macronutrient Oxidation in Response to an Individualized Nonshivering Cooling Protocol

OBJECTIVE

This study aimed to describe the energy expenditure (EE) and macronutrient oxidation response to an individualized nonshivering cold exposure in young healthy adults.

METHODS

Two different groups of 44 (study 1: 22.1  [SD 2.1] years old, 25.6  [SD 5.2] kg/m² , 34% men) and 13 young healthy adults (study 2: 25.6  [SD 3.0] years old, 23.6  [SD 2.4] kg/m² , 54% men) participated in this study. Resting metabolic rate (RMR) and macronutrient oxidation rates were measured by indirect calorimetry under fasting conditions in a warm environment (for 30 minutes) and in mild cold conditions (for 65 minutes, with the individual wearing a water-perfused cooling vest set at an individualized temperature adjusted to the individual's shivering threshold).

RESULTS

In study 1, EE increased in the initial stage of cold exposure and remained stable for the whole cold exposure (P < 0.001). Mean cold-induced thermogenesis (9.56 ± 7.9 kcal/h) was 13.9% ± 11.6% of the RMR (range: -14.8% to 39.9% of the RMR). Carbohydrate oxidation decreased during the first 30 minutes of the cold exposure and later recovered up to the baseline values (P < 0.01) in parallel to opposite changes in fat oxidation (P < 0.01). Results were replicated in study 2.

CONCLUSIONS

A 1-hour mild cold exposure individually adjusted to elicit maximum nonshivering thermogenesis induces a very modest increase in EE and a shift of macronutrient oxidation that may underlie a shift in thermogenic tissue activity.

Association between dietary factors and brown adipose tissue volume/18F-FDG uptake in young adults

OBJECTIVE

To study the association between usual dietary factors (dietary energy density, nutrient intake, food group consumption, and dietary pattern) and brown adipose tissue (BAT) volume/¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) uptake after personalized cold exposure in young healthy adults.

METHODS

A total of 122 young adults (n = 82 women; 22.0 ± 2.1 years old; 24.8 ± 4.8 kg/m²) took part in this cross-sectional study. Dietary factors were measured via a food frequency questionnaire and three non-consecutive 24 h recalls. Dietary energy density (foods and caloric beverages included) and macronutrient intakes were subsequently estimated using EvalFINUT® software, food group consumption was estimated from the food frequency questionnaire, and different dietary patterns and quality indices were determined according to the reference methods. BAT volume, BAT ¹⁸F-FDG uptake, and skeletal muscle ¹⁸F-FDG uptake were assessed by static ¹⁸F-FDG positron-emission tomography and computed tomography (PET-CT) scans after a 2 h personalized exposure to cold.

RESULTS

A direct association was detected between dietary energy density and BAT Standardized Uptake Value (SUV)mean (β = 0.215; R² = 0.044; P = 0.022), and between ethanol consumption and BAT volume (β = 0.215; R² = 0.044; P = 0.022). The a priori Mediterranean dietary pattern was inversely associated with BAT SUVmean and SUVpeak (β = -0.273; R² = 0.075; P = 0.003 and β = -0.255; R² = 0.066; P = 0.005 respectively). In addition, the diet quality index for a Mediterranean diet and a pro-inflammatory dietary pattern (as determined via the dietary inflammatory index) were directly associated with BAT SUVmean and SUVpeak (SUVmean: β = 0.238; R² = 0.053; P = 0.013 and β = 0.256; R² = 0.052; P = 0.012 respectively; SUVpeak: β = 0.278; R² = 0.073; P = 0.003 and β = 0.248; R² = 0.049; P = 0.016 respectively). After controlling for multiplicity and possible confounders (sex, the evaluation wave and BMI), all the detected associations persisted.

CONCLUSION

Dietary factors are slightly associated with BAT volume and/or ¹⁸F-FDG uptake after a personalized cold exposure in young adults. Our results provide an overall picture of the potential relationships between dietary factors and BAT-related variables in humans.

Beyond general resistance training. Hypertrophy versus muscular endurance training as therapeutic interventions in adults with type 2 diabetes mellitus: A systematic review and meta-analysis

Resistance training (RT) is a powerful first-line intervention for the management of type 2 diabetes mellitus (T2DM). Nonetheless, the effects of the most frequent RT (hypertrophy training [HT] and muscular endurance training [MERT]) employed for the management of T2DM, and which type of RT might exert superior effects, remain elusive. Thus, this review aims to assess the effects of HT and MERT on glycaemic control, physical fitness, body composition, lipid profile, blood pressure, C-reactive protein, and quality of life in patients with T2DM; to analyse which particular RT is more effective; to assess the effects of general RT; and to identify RT components, characteristics of patients, and medications that could mediate the effects of RT. Randomized controlled trials (RCT) and non-RCT (RT≥ 4 weeks) in adults with T2DM were selected. Both HT and MERT improved HbA1c, insulin levels and sensitivity, muscle strength, body mass index, waist circumference, and fat mass. Additionally, HT improved glucose, cardiorespiratory fitness, fat percentage, lean body mass, lipid profile, systolic blood pressure, and C-reactive protein, and MERT improved weight. Overall, HT and MERT exert beneficial effects well comparable with aerobic training. Both types of RT can be used as potent therapeutic interventions for the management of T2DM depending on patients' limitations/preferences.

Body Composition Impact on Sleep in Young Adults: The Mediating Role of Sedentariness, Physical Activity, and Diet

Obesity and sleep disturbances are both related to endocrine and metabolic alterations, cardiovascular disease, and impaired daytime functioning and mood. However, the bidirectional relationship between these conditions and the underlying mechanisms still remain unclear. This study aimed to investigate the potential association of anthropometric and body composition parameters with sleep in young adults, considering the mediating role of sedentariness, physical activity, and diet. A total of 187 adults aged 18–25 (35.29% men) participated in the study. Body mass index (BMI), waist–hip ratio, and waist–height ratio were calculated, and a dual-energy X-ray absorptiometry scanner was used to assess body composition. Sedentary time and physical activity, as well as sleep duration and quality, were objectively and subjectively measured using accelerometry and the Pittsburgh Sleep Quality Index. An inverse association was found between BMI and total sleep time (β = −0.165, p = 0.029). Waist–hip ratio and lean mass index were also negatively associated with total sleep time (β = −0.222, p = 0.007, and β = −0.219, p = 0.004) and sleep efficiency (β = −0.174, p = 0.037, and β = −0.188, p = 0.013). Sedentary time moderated by sex explained the association of BMI with total sleep time such that a high BMI was related to higher sedentariness in men which, in turn, was significantly associated with shorter sleep duration. Sedentary time is, therefore, a link/risk factor mediating the association of high BMI with short sleep duration in healthy young men.

Sleep duration and quality are not associated with brown adipose tissue volume or activity-as determined by 18F-FDG uptake, in young, sedentary adults

Study Objectives

Short sleep duration and sleep disturbances have been related to obesity and metabolic disruption. However, the behavioral and physiological mechanisms linking sleep and alterations in energy balance and metabolism are incompletely understood. In rodents, sleep regulation is closely related to appropriate brown adipose tissue (BAT) thermogenic activity, but whether the same is true in humans has remained unknown. The present work examines whether sleep duration and quality are related to BAT volume and activity (measured by ¹⁸F-FDG) and BAT radiodensity in humans.

Methods

A total of 118 healthy adults (69% women, 21.9 ± 2.2 years, body mass index: 24.9 ± 4.7 kg/m²) participated in this cross-sectional study. Sleep duration and other sleep variables were measured using a wrist-worn accelerometer for seven consecutive days for 24 hours per day. The Pittsburgh Sleep Quality Index was used to assess sleep quality. All participants then underwent a personalized cold exposure to determine their BAT volume, activity, and radiodensity (a proxy of the intracellular triglyceride content), using static positron emission tomography combined with computed tomography (PET/CI) scan.

Results

Neither sleep duration nor quality was associated with BAT volume or activity (the latter represented by the mean and peak standardized ¹⁸F-FDG uptake values) or radiodensity (all p > .1). The lack of association remained after adjusting the analyses for sex, date of PET/CT, and body composition.

Conclusions

Although experiments in rodent models indicate a strong relationship to exist between sleep regulation and BAT function, it seems that sleep duration and quality may not be directly related to the BAT variables examined in the present work.

Clinical Trial Registration

NCT02365129 (ClinicalTrials.gov).

Brown adipose tissue volume and 18F-fluorodeoxyglucose uptake are not associated with energy intake in young human adults

BACKGROUND

Several studies have explored the role of human brown adipose tissue (BAT) in energy expenditure. However, the link between BAT and appetite regulation needs to be more rigorously examined.

OBJECTIVES

We aimed to investigate the associations of BAT volume and 18F-fluordeoxyglucose (18F-FDG) uptake after a personalized cold exposure with energy intake and appetite-related sensations in young healthy humans.

METHODS

A total of 102 young adults (65 women; age: 22.08 ± 2.17 y; BMI: 25.05 ± 4.93 kg/m 2) took part in this cross-sectional study. BAT volume, BAT 18F-FDG uptake, and skeletal muscle 18F-FDG uptake were assessed by means of static 18F-FDG positron-emission tomography and computed tomography scans after a 2-h personalized exposure to cold. Energy intake was estimated via an objectively measured ad libitum meal and three nonconsecutive 24-h dietary recalls. Appetite-related sensations (i.e., hunger and fullness) were recorded by visual analog scales before and after a standardized breakfast (energy content = 50% of basal metabolic rate) and the ad libitum meal. Body composition was assessed by a whole-body DXA scan.

RESULTS

BAT volume and 18F-FDG uptake were not associated with quantified ad libitum energy intake (all P > 0.088), nor with habitual energy intake estimated from the 24-h dietary recalls (all P  > 0.683). Lean mass was positively associated with both the energy intake from the ad libitum meal (β: 17.612, R2 = 0.213; P < 0.001) and the habitual energy intake (β: 16.052, R2 = 0.123; P = 0.001). Neither the interaction BAT volume × time elapsed after meal consumption nor that of BAT 18F-FDG uptake × time elapsed after meal consumption had any significant influence on appetite-related sensations after breakfast or after meal consumption (all P > 0.3).

CONCLUSIONS

Neither BAT volume, nor BAT 18F-FDG uptake after cold stimulation, are related to appetite regulation in young adults. These results suggest BAT plays no important role in the regulation of energy intake in humans.This trial was registered at clinicaltrials.gov as NCT02365129.

Impact of Using Different Levels of Threshold-Based Artefact Correction on the Quantification of Heart Rate Variability in Three Independent Human Cohorts

Heart rate variability (HRV) is a non-invasive indicator of autonomic nervous system function. HRV recordings show artefacts due to technical and/or biological issues. The Kubios software is one of the most used software to process HRV recordings, offering different levels of threshold-based artefact correction (i.e., Kubios filters). The aim of the study was to analyze the impact of different Kubios filters on the quantification of HRV derived parameters from short-term recordings in three independent human cohorts. A total of 312 participants were included: 107 children with overweight/obesity (10.0 ± 1.1 years, 58% men), 132 young adults (22.2 ± 2.2 years, 33% men) and 73 middle-aged adults (53.6 ± 5.2 years, 48% men). HRV was assessed using a heart rate monitor during 10–15 min, and the Kubios software was used for HRV data processing using all the Kubios filters available (i.e., 6). Repeated-measures analysis of variance indicated significant differences in HRV derived parameters in the time-domain (all p < 0.001) across the Kubios filters in all cohorts, moreover similar results were observed in the frequency-domain. When comparing two extreme Kubios filters, these statistical differences could be clinically relevant, e.g. more than 10 ms in the standard deviation of all normal R-R intervals (SDNN). In conclusion, the results of the present study suggest that the application of different Kubios filters had a significant impact on HRV derived parameters obtained from short-term recordings in both time and frequency-domains.

Comparability of accelerometer signal aggregation metrics across placements and dominant wrist cut points for the assessment of physical activity in adults

Large epidemiological studies that use accelerometers for physical behavior and sleep assessment differ in the location of the accelerometer attachment and the signal aggregation metric chosen. This study aimed to assess the comparability of acceleration metrics between commonly-used body-attachment locations for 24 hours, waking and sleeping hours, and to test comparability of PA cut points between dominant and non-dominant wrist. Forty-five young adults (23 women, 18–41 years) were included and GT3X + accelerometers (ActiGraph, Pensacola, FL, USA) were placed on their right hip, dominant, and non-dominant wrist for 7 days. We derived Euclidean Norm Minus One g (ENMO), Low-pass filtered ENMO (LFENMO), Mean Amplitude Deviation (MAD) and ActiGraph activity counts over 5-second epochs from the raw accelerations. Metric values were compared using a correlation analysis, and by plotting the differences by time of the day. Cut points for the dominant wrist were derived using Lin’s concordance correlation coefficient optimization in a grid of possible thresholds, using the non-dominant wrist estimates as reference. They were cross-validated in a separate sample (N = 36, 10 women, 22–30 years). Shared variances between pairs of acceleration metrics varied across sites and metric pairs (range in r²: 0.19–0.97, all p < 0.01), suggesting that some sites and metrics are associated, and others are not. We observed higher metric values in dominant vs. non-dominant wrist, thus, we developed cut points for dominant wrist based on ENMO to classify sedentary time (<50 mg), light PA (50–110 mg), moderate PA (110–440 mg) and vigorous PA (≥440 mg). Our findings suggest differences between dominant and non-dominant wrist, and we proposed new cut points to attenuate these differences. ENMO and LFENMO were the most similar metrics, and they showed good comparability with MAD. However, counts were not comparable with ENMO, LFENMO and MAD.

Objective and subjective measures of physical functioning in women with fibromyalgia: what type of measure is associated most clearly with subjective well-being?

PURPOSE

To find modifiable factors that are related to subjective well-being would be valuable for improving interventions in fibromyalgia. Physical activity, sedentary behaviour, and physical fitness may represent potential areas to optimize treatment regimens. In fibromyalgia, there is a discordance between clinical observations and patient-reported outcomes (objective and subjective assessments). Therefore, the present study aims at analyzing the associations of objective and subjective evaluations of physical activity, sedentary behaviour, and physical fitness with subjective well-being and determine if and how objective and subjective associations differ.

METHODS

In this population-based cross-sectional study participated 375 women with fibromyalgia from the al-Ándalus project (Spain). Physical activity, sedentary behaviour, and physical fitness were objectively (accelerometers and performance testing) and subjectively (questionnaires) measured. Participants self-reported their levels of positive affect, negative affect, and life satisfaction.

RESULTS

In the most conservative multivariate analysis, we found independent associations of the objective measures of physical activity with positive affect and life satisfaction and sedentary behaviour with positive affect. No such relationship was seen with subjective measures of the same behaviours. Moreover, we observed that objective and subjective physical fitness evaluations were independent of each other related to subjective well-being.

CONCLUSIONS

Independent associations of the objective measures (but not the subjective assessments) of physical activity with positive affect and life satisfaction, and of sedentary behaviour with positive affect were observed. However, objective measures and subjective appraisals of physical fitness appear to be independently related to well-being, which should be considered when developing physical exercise interventions for fibromyalgia.Implications for rehabilitationThe analysis of concurrent associations of objective and subjective evaluations of physical functioning with subjective well-being offers indications for modifiable targets in rehabilitation that can improve well-being in fibromyalgia.Exercise-based rehabilitation may help women with fibromyalgia to improve subjective well-being, particularly positive affect.Rehabilitation should focus on both the objective physical performance of women with fibromyalgia and on their perceptions of what they can do physically.When rehabilitation aims at enhancing positive affect or life satisfaction by changing the lifestyle of women with fibromyalgia, physical activity and sedentary behaviour should be objectively monitored.

Relationship between the Daily Rhythm of Distal Skin Temperature and Brown Adipose Tissue 18F-FDG Uptake in Young Sedentary Adults

The present study examines whether the daily rhythm of distal skin temperature (DST) is associated with brown adipose tissue (BAT) metabolism as determined by ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) uptake in young adults. Using a wireless thermometer (iButton) worn on the nondominant wrist, DST was measured in 77 subjects (26% male; age 22 ± 2 years; body mass index 25.2 ± 4.8 kg/m²) for 7 consecutive days. The temperatures to which they were habitually exposed over the day were also recorded. The interday stability of DST was calculated from the collected data, along with the intraday variability and relative amplitude; the mean temperature of the 5 and 10 consecutive hours with the maximum and minimum DST values, respectively; and when these hours occurred. Following exposure to cold, BAT volume and mean and peak standardized ¹⁸F-FDG uptake (SUV_mean and SUV_peak) were determined for each subject via static ¹⁸F-FDG positron emission tomography/computed tomography scanning. Relative amplitude and the time at which the 10 consecutive hours of minimum DST values occurred were positively associated with BAT volume, SUV_mean, and SUV_peak (p ≤ 0.02), whereas the mean DST of that period was inversely associated with the latter BAT variables (p ≤ 0.01). The interday stability and intraday variability of the DST were also associated (directly and inversely, respectively) with BAT SUV_peak (p ≤ 0.02 for both). All of these associations disappeared, however, when the analyses were adjusted for the ambient temperature to which the subjects were habitually exposed. Thus, the relationship between the daily rhythm of DST and BAT activity estimated by ¹⁸F-FDG uptake is masked by environmental and likely behavioral factors. Of note is that those participants exposed to the lowest ambient temperature showed 3 to 5 times more BAT volume and activity compared with subjects who were exposed to a warmer ambient temperature.

Relationships between cardiorespiratory fitness/muscular strength and 18F-fluorodeoxyglucose uptake in brown adipose tissue after exposure to cold in young, sedentary adults

Humans have metabolically active brown adipose tissue (BAT). However, what is the relation between exercise or physical activity with this tissue remains controversial. Therefore, the main aim of the present study is to examine whether cardiorespiratory fitness and muscular strength are associated with brown adipose tissue (BAT) volume and activity after exposure to cold in young, sedentary adults. Cardiorespiratory fitness was determined in 119 young, healthy, sedentary adults (68% women, age 21.9 ± 2.1 years, body mass index 25 ± 4.8 kg/m2) via the maximum treadmill exercise test, and their muscular strength assessed by the handgrip strength test and the 1-repetition maximum bench and leg press tests. Some days later, all subjects were exposed to 2 h of personalized exposure to cold and their cold-induced BAT volume and activity determined by a combination of 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography and computed tomography scan. Cardiorespiratory fitness was associated with neither the BAT volume nor BAT activity (P ≥ 0.05). However, handgrip strength with respect to lean body mass was positively (though weakly) associated with BAT activity as represented by the 18F-FDG mean standardised uptake value (SUV) (β = 3.595, R2 = 0.039, P = 0.031) and SUVpeak value (β = 15.314, R2 = 0.037, P = 0.035). The above relationships remained after adjusting for several confounders. No other associations were found. Handgrip strength with respect to lean body mass is positively associated with BAT activity (SUVmean and SUVpeak) in young adults after exposure to cold - but only weakly. Further studies are needed to reveal the relationship between muscular fitness and human BAT characteristics.

Energy expenditure differences across lying, sitting, and standing positions in young healthy adults

The time spent in sedentary behaviour represents an important public health burden. To reduce sedentary time in the general population, the simplest, most effective, and most accessible method is to decrease lying and sitting time. We aimed to compare differences on energy expenditure (EE) across lying, sitting, and standing positions; and to analyse the associations between the change on EE of changing from one position to another and anthropometric and body composition parameters in young healthy adults. A total of 55 (69% women) young healthy adults aged 21.7 ± 2.2 participated in the study. We measured EE by indirect calorimetry across lying, sitting, and standing positions following the standard procedures. The EE was significantly higher in standing than in both lying and sitting positions (mean difference: 0.121±0.292 and 0.125±0.241 kcal/min, respectively; all P<0.001), and no differences were observed between lying and sitting positions (P = 1.000). There was a negative association between the EE differences in sitting vs. standing position and lean body mass (P = 0.048), yet no associations between EE differences with the rest of the anthropometric and body composition parameters were observed in each position pair studied (all P>0.321). Our findings support the fact that increasing the time spent standing could be a simple strategy to slightly increase EE. Therefore, our results have important clinical implications including a better monitoring, characterizing, and promoting countermeasures to sedentariness through low-level physical activities.

The Mediating Role of Brown Fat and Skeletal Muscle Measured by 18 F-Fluorodeoxyglucose in the Thermoregulatory System in Young Adults

OBJECTIVE

This study aimed to examine whether brown adipose tissue (BAT) or skeletal muscle activity mediates the relationship between personal level of environmental temperature (Personal-ET) and wrist skin temperature (WT). Moreover, we examined whether BAT and skeletal muscle have a mediating role between Personal-ET and WT (as a proxy of peripheral vasoconstriction/vasodilation).

METHODS

The levels of BAT were quantified by cold-induced ¹⁸ F-fluorodeoxyglucose-positron emission tomography/computed tomography scan and measured the Personal-ET and WT by using iButtons (Maxim Integrated, Dallas, Texas) in 75 participants (74.6% women).

RESULTS

The study found that BAT volume and metabolic activity played a positive and significant role (up to 25.4%) in the association between Personal-ET and WT. In addition, at the coldest temperatures, the participants with lower levels of WT (inducing higher peripheral vasoconstriction) had higher levels of BAT outcomes, whereas in warm temperatures, participants with higher levels of WT (inducing higher peripheral vasodilation) had lower levels of BAT outcomes. The study did not find any mediating role of skeletal muscle activity.

CONCLUSIONS

BAT volume and metabolic activity play a role in the relationship between Personal-ET and WT. Moreover, the data suggest that there are two distinct phenotypes: individuals who respond better to the cold, both through nonshivering thermogenesis and peripheral vasoconstriction, and individuals who respond better to the heat.

Supraclavicular skin temperature measured by iButtons and 18F-fluorodeoxyglucose uptake by brown adipose tissue in adults

Currently, 18 [F]-Fluorodeoxyglucose (¹⁸F-FDG) in combination with a positron emission tomography/computed tomography (PET/CT) scan analysis is the most commonly used method to quantify human BAT volume and activity. However, this technique presents several drawbacks which negatively affect participant's health. The aim of the present work is to determine whether supraclavicular skin temperature can be used as an indirect marker of cold-induced BAT and skeletal muscle ¹⁸F-FDG uptake in adults, while taking into account body composition. We performed a personalized cooling protocol just before an ¹⁸F-FDG-PET/CT scan, and we measured supraclavicular skin temperature before (in warm conditions) and after the cooling protocol in 88 adults (n = 57 women, mean age: 21.9 ± 2.1 years old, body mass index: 24.5 ± 4.3 km/m²). We found that supraclavicular skin temperature at the warm and cold periods was weakly and positively associated with BAT activity (SUV_mean and SUV_peak: β = 3.000; R² = 0.072; P = 0.022 and β = 2.448; R² = 0.060; P = 0.021), but not with skeletal muscle ¹⁸F-FDG uptake, after controlling for body composition. We performed further analyses and the positive associations persisted only in the group of women. In conclusion, supraclavicular skin temperature in warm and cold conditions seems to be related with cold-induced ¹⁸F-FDG uptake by BAT only in women, although the low explained variance of these associations means that there are other factors involved in the supraclavicular skin temperature.

Concurrent validity of supraclavicular skin temperature measured with iButtons and infrared thermography as a surrogate marker of brown adipose tissue

Brown adipose tissue (BAT) thermogenic activity is commonly assessed with a positron emission tomography with computed tomography scan (PET/CT). This technique has several limitations and alternative techniques are needed. Supraclavicular skin temperature measured with iButtons and infrared thermography (IRT) has been proposed as an indirect marker of BAT activity. We studied the concurrent validity of skin temperature measured with iButtons vs. IRT and the association of supraclavicular skin temperature measured with iButtons and IRT with BAT. We measured skin temperature upon a shivering threshold test with iButtons and IRT in 6 different regions in 12 participants (n = 2 men). On a separate day, we determined supraclavicular skin temperature with an iButton and IRT after 2 h of a personalized cooling protocol. Thereafter, we quantified BAT volume and activity by PET/CT. We observed that the absolute differences between the devices were statistically different from 0 (all P < 0.05) after the shivering threshold test. Moreover, we did not find any association between supraclavicular skin temperature measured with iButtons or IRT and BAT ¹⁸F-FDG activity (r = -0.213; P = 0.530 and r = -0.079; P = 0.817). However, we observed a negative association of supraclavicular skin temperature measured by IRT with BAT ¹⁸F-FDG volume (r = -0.764; P = 0.006), but not with supraclavicular skin temperature measured with iButtons (r = -0.546; P = 0.082). In light of these results, we concluded that the measurement of skin temperature obtained by iButtons and IRT are not comparable. Furthermore, it seems that supraclavicular skin temperature is not associated with BAT ¹⁸F-FDG activity, but it appears to be negatively associated with BAT ¹⁸F-FDG volume in the case of IRT.

Association of Objectively Measured Physical Activity With Brown Adipose Tissue Volume and Activity in Young Adults

PURPOSE

Human brown adipose tissue (BAT) has gained considerable attention as a potential therapeutic target for obesity and type 2 diabetes; however, whether physical activity (PA) might be an efficient stimulus to activate and recruit BAT remains to be ascertained. We aimed to examine whether objectively measured PA levels were associated with BAT volume and activity in young sedentary adults. We additionally examined the association of PA levels with the skeletal muscles activity.

METHODS

A total of 130 young healthy and sedentary adults (67% women; age, 21.9 ± 2.1 years old; body mass index, 25 ± 4.8 kg/m2) participated in this cross-sectional study. PA was objectively measured with a wrist-worn accelerometer for 7 consecutive days. Age-specific cut points were applied to classify wrist accelerations into sedentary time and different PA intensities (i.e., light, moderate, vigorous, moderate-vigorous). The participants underwent 2 hours of a personalized cold exposure to determine the cold-induced BAT volume and activity and the skeletal muscles activity by means of an 18F-fluorodeoxyglucose positron emission tomography combined with a CT scan.

RESULTS

Objectively measured PA intensity levels were neither associated with BAT volume and activity nor with the skeletal muscles activity (all P > 0.05). The results remained after adjusting for sex, waking time, and environmental temperature.

CONCLUSIONS

Although PA plays an important role in the prevention of obesity and related comorbidities, it seems that other physiological mechanisms rather than brown adipocyte activation or recruitment might moderate its beneficial metabolic effects in young sedentary adults.

Evidence of high 18 F-fluorodeoxyglucose uptake in the subcutaneous adipose tissue of the dorsocervical area in young adults

NEW FINDINGS

What is the central question of this study? In some studies, biopsies have been performed of the subcutaneous adipose tissue in the abdomen, and they failed to find browning markers. Is the abdomen the right place to take biopsies? What is the main finding and its importance? For first time, we observed that the glucose uptake in the dorsocervical subcutaneous adipose tissue is higher in comparison to other areas of subcutaneous adipose tissue.

ABSTRACT

Neonates have subcutaneous brown adipose tissue (BAT) in the dorsocervical area, and it is thought that these depots gradually disappear with age. Here, we determined that young adults have high ¹⁸ F-flurodeoxyglucose (¹⁸ F-FDG) uptake in the subcutaneous adipose tissue (SAT) of the dorsocervical area. A total of 133 young adults (age 22 ± 2 years; body mass index 25 ± 5 kg m² ) were included in the study. We performed a shivering threshold test for every participant. Later, we performed 2 h of personalized cold exposure, immediately before a positron emission tomography/computed tomography scan. We showed that 23 of 133 participants had ¹⁸ F-FDG uptake in the dorsocervical area that achieved the criteria to be considered BAT, mainly in women (96%, n = 22 of 23). In the whole sample, the glucose uptake in the SAT of the dorsocervical area was positively correlated with BAT volume and activity located in the supraclavicular area. We showed that the ¹⁸ F-FDG uptake of the SAT of the dorsocervical area in humans is different from that of other SAT areas. Future studies are warranted to confirm the brown signature of this tissue.

Association of wrist and ambient temperature with cold-induced brown adipose tissue and skeletal muscle [18F]FDG uptake in young adults

Brown adipose tissue (BAT) activity is influenced by the outdoor temperature variation. However, people spend most of their time indoors, especially in colder regions and during cold seasons. Therefore, outdoor temperature is probably not an accurate tool to quantify the exposure of the participants before BAT quantification. We studied the association of wrist and personal environmental temperatures with cold-induced BAT and skeletal muscle [18F]fluorodeoxyglucose ([18F]FDG) uptake in adults. A total of 74 participants wore two iButtons during 7 days to measure wrist temperature (WT) and personal level of environmental temperature (Personal-ET). Thereafter, we performed a 2-h personalized cooling protocol before performing an [18F]FDG-PET/CT scan. WT was negatively associated with BAT volume ( R2 = 0.122; P = 0.002) and BAT activity [standardized uptake value (SUV)peak, R2 = 0.083; P = 0.012]. Moreover, Personal-ET was negatively associated with BAT volume ( R2 = 0.164; P < 0.001), BAT activity (SUVmean and SUVpeak, all R2 ≥ 0.167; P < 0.001), and skeletal muscle activity (SUVpeak, R2 = 0.122; P = 0.002). Interestingly, the time exposed to a certain Personal-ET (16–20°C) positively correlated only with [18F]FDG uptake by BAT (volume and activity; all P ≤ 0.05), whereas the time exposed to 12–15°C positively correlated only with measures of [18F]FDG uptake by skeletal muscle activity (all P ≤ 0.05). This study shows that WT and Personal-ET are associated with [18F]FDG uptake by BAT and skeletal muscle activity in adults within certain temperature thresholds. Moreover, our results suggest that [18F]FDG uptake by human BAT or skeletal muscle can be activated or inhibited in different ranges of ambient temperatures exposures. Results should be taken with caution because the observed associations were relatively weak.

Brown Adipose Tissue and Skeletal Muscle 18F-FDG Activity After a Personalized Cold Exposure Is Not Associated With Cold-Induced Thermogenesis and Nutrient Oxidation Rates in Young Healthy Adults

Cold induced thermogenesis (CIT) in humans results mainly from the combination of both brown adipose tissue (BAT) and skeletal muscle thermogenic activity. The relative contribution of both tissues to CIT and to cold induced nutrient oxidation rates (CI-NUTox) remains, however, to be elucidated. We investigated the association of BAT and skeletal muscle activity after a personalized cold exposure with CIT and CI-NUTox in 57 healthy adults (23.0 ± 2.4 years old; 25.1 ± 4.6 kg/m²; 35 women). BAT and skeletal muscle (paracervical, sternocleidomastoid, scalene, longus colli, trapezius, parathoracic, supraspinatus, subscapular, deltoid, pectoralis major, and triceps brachii) metabolic activity were assessed by means of a ¹⁸Fluorodeoxyglucose positron emission tomography-computed tomography scan preceded by a personalized cold exposure. The cold exposure consisted in remaining in a mild cold room for 2 h at 19.5–20°C wearing a water perfused cooling vest set at 3.8°C above the individual shivering threshold. On a separate day, we estimated CIT and CI-NUTox by indirect calorimetry under fasting conditions for 1 h of personalized cold exposure. There was no association of BAT volume or activity with CIT or CI-NUTox (all P > 0.2). Similarly, the skeletal muscle metabolic activity was not associated either with CIT or CI-NUTox (all P > 0.2). The results persisted after controlling for sex, the time of the day, and the date when CIT was assessed. Our results suggest that human BAT activity and skeletal muscle ¹⁸F-FDG activity are not associated to CIT in young healthy adults. Inherent limitations of the available radiotracers for BAT detection and muscle activity quantification may explain why we failed to detect a physiologically plausible association.

Physiological responses to acute cold exposure in young lean men

The aim of this study was to comprehensively describe the physiological responses to an acute bout of mild cold in young lean men (n = 11, age: 23 ± 2 years, body mass index: 23.1 ± 1.2 kg/m2) to better understand the underlying mechanisms of non-shivering thermogenesis and how it is regulated. Resting energy expenditure, substrate metabolism, skin temperature, thermal comfort perception, superficial muscle activity, hemodynamics of the forearm and abdominal regions, and heart rate variability were measured under warm conditions (22.7 ± 0.2°C) and during an individualized cooling protocol (air-conditioning and water cooling vest) in a cold room (19.4 ± 0.1°C). The temperature of the cooling vest started at 16.6°C and decreased ~ 1.4°C every 10 minutes until participants shivered (93.5 ± 26.3 min). All measurements were analysed across 4 periods: warm period, at 31% and at 64% of individual´s cold exposure time until shivering occurred, and at the shivering threshold. Energy expenditure increased from warm period to 31% of cold exposure by 16.7% (P = 0.078) and to the shivering threshold by 31.7% (P = 0.023). Fat oxidation increased by 72.6% from warm period to 31% of cold exposure (P = 0.004), whereas no changes occurred in carbohydrates oxidation. As shivering came closer, the skin temperature and thermal comfort perception decreased (all P<0.05), except in the supraclavicular skin temperature, which did not change (P>0.05). Furthermore, the superficial muscle activation increased at the shivering threshold. It is noteworthy that the largest physiological changes occurred during the first 30 minutes of cold exposure, when the participants felt less discomfort.

Differences between the most used equations in BAT-human studies to estimate parameters of skin temperature in young lean men

Cold exposure is necessary to activate human brown adipose tissue (BAT), resulting in heat production. Skin temperature is an indirect measure to monitor the body's reaction to cold. The aim of this research was to study whether the most used equations to estimate parameters of skin temperature in BAT-human studies measure the same values of temperature in young lean men (n = 11: 23.4 ± 0.5 years, fat mass: 19.9 ± 1.2%). Skin temperature was measured with 26 ibuttons at 1-minute intervals in warm and cold room conditions. We used 12 equations to estimate parameters of mean, proximal, and distal skin temperature as well as skin temperature gradients. Data were analysed with Temperatus software. Significant differences were found across equations to measure the same parameters of skin temperature in warm and cold room conditions, hampering comparison across studies. Based on these findings, we suggest to use a set of 14 ibuttons at anatomical positions reported by ISO STANDARD 9886:2004 plus five ibuttons placed on the right supraclavicular fossa, right middle clavicular bone, right middle upper forearm, right top of forefinger, and right upper chest.