Resting Energy Expenditure: From Cellular to Whole-Body Level, a Mechanistic Historical Perspective

Fluorescence Spectroscopy With Temperature Functional Tests in the Assessment of Markers of Intracellular Energy Metabolism: Spatial Heterogeneity and Reproducibility of Measurements

The fluorescence intensities of the cellular respiratory cofactors NADH (reduced nicotinamide adenine dinucleotide) and FAD++ (oxidized flavin adenine dinucleotide) reflect energy metabolism in skin and other tissues and can be quantified in vivo by fluorescence spectroscopy (FS). However, the variability of physiological parameters largely determines the reproducibility of measurement results and the reliability of the diagnostic test. In this prospective study, we evaluated the interday reproducibility of NADH and FAD++ fluorescence intensity measurements in the skin of 51 healthy volunteers assessed by the FS at baseline, after local cooling (10°C) and heating of the skin (35°C). Results showed that the fluorescence amplitude of NADH (AFNADH) in forearm skin was the most reproducible of the FS parameters studied. Assessment of AFNADH in the dorsal forearm in combination with a thermal functional test is the most promising method for clinical use for assessing energy metabolism in the skin.

Iron supplementation and iron accumulation promote adipocyte thermogenesis through PGC1α-ATGL-mediated lipolysis

Iron homeostasis is essential for maintaining metabolic health and iron disorder has been linked to chronic metabolic diseases. Increasing thermogenic capacity in adipose tissue has been considered as a potential approach to regulate energy homeostasis. Both Mitochondrial biogenesis and mitochondrial function are iron dependent and essential for adipocyte thermogenic capacity, but the underlying relationships between iron accumulation and adipose thermogenesis is unclear. Firstly, we confirmed that iron homeostasis and the iron regulatory markers (e.g. Tfr1, Hfe) are involved in cold induced thermogenesis in subcutaneous adipose tissues using RNA-seq and bioinformatic analysis. Secondly, an Hfe (Hfe-/-) deficient mouse model, in which tissues become overloaded with iron, was employed. We found iron accumulation caused by Hfe deficiency enhanced mitochondrial respiratory chain expression in subcutaneous white adipose in vivo and resulted in enhanced tissue thermogenesis with upregulation of PGC-1α and ATGL, mitochondrial biogenesis and lipolysis. To investigate the thermogenic capacity in vitro, stromal vascular fraction (SVF) from adipose tissues was isolated, followed with adipogenic differentiation. Primary adipocyte from Hfe-/- mice exhibited higher cellular oxygen consumption, associated with enhanced expression of mitochondrial oxidative respiratory chain protein, while primary adipocytes or SVFs from WT mice supplemented with iron citrate (FAC) exhibited similar effect in thermogenic capacity. Taken together, these findings indicate iron supplementation and iron accumulation (Hfe deficiency) can regulate adipocyte thermogenic capacity, suggesting a potential role for iron homeostasis in adipose tissues.

Resting energy expenditure in women with polycystic ovary syndrome

STUDY QUESTION

Is resting energy expenditure (REE) altered in women with polycystic ovary syndrome (PCOS)?

SUMMARY ANSWER

Women with PCOS have a reduction in REE, when corrected for fat-free mass, independent of PCOS clinical phenotypes and BMI categories.

WHAT IS KNOWN ALREADY

Obesity is an important issue in women with PCOS, in terms of frequency and pathophysiological implications. It has been hypothesized that obesity may be favoured by alterations in REE, but the studies have been limited and conflicting.

STUDY DESIGN, SIZE, DURATION

This case-control study was a comparison of 266 women with PCOS and 51 healthy controls, recruited in the Verona 3P study from 2010 to 2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Women with PCOS diagnosed by the Rotterdam criteria, with normal thyroid function and no interfering medications, were referred to the outpatient clinic of a tertiary care centre of endocrinology and metabolism for a measurement of REE. Healthy controls were recruited in the same period and submitted to the same procedure. In all subjects, REE was measured by indirect calorimetry and serum androgens were measured by LC-MS/MS. In women with PCOS, insulin sensitivity was assessed using the hyperinsulinemic-euglycemic clamp.

MAIN RESULTS AND THE ROLE OF CHANCE

REE was similar in women with PCOS and controls. However, REE corrected for fat-free mass (REE/FFM) was significantly lower in women with PCOS than in controls (31.8 ± 4.0 vs 35.4 ± 3.9 kcal/kgFFM·day, P < 0.001). REE/FFM did not differ between normal-weight, overweight, or obese women with PCOS, and each of these subgroups showed lower REE/FFM values than controls. Reduced REE/FFM values were found in each phenotype of the syndrome. In multiple regression analysis, REE/FFM was independently associated with age and PCOS status, but not with fat mass. In PCOS women, REE/FFM was independently and directly associated with ovarian follicle number.

LIMITATIONS, REASONS FOR CAUTION

Limitations of the study are the cross-sectional design, which limits the causal inference of the results, and the unavailability of precise information about lifestyle factors, which may be potential confounders. Further prospective studies are needed to establish the importance of this phenomenon in contributing to the weight excess of PCOS.

WIDER IMPLICATIONS OF THE FINDINGS

A reduction of REE could potentially favour weight gain in women with PCOS and possibly contribute to the altered metabolic profile typical of this condition, even counteracting the therapeutic strategies aimed to reduce excess body fat in these women. Nevertheless, the presence of this abnormality in both obese/overweight and normal-weight patients suggests that other factors must play a role in this phenomenon.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by academic grants to PM from the University of Verona (FUR 2010-2022). All authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Estrogen deficiency reduces maximal running capacity and affects serotonin levels differently in the hippocampus and nucleus accumbens in response to acute exercise

Introduction

Estrogen deficiency is associated with unfavorable changes in body composition and metabolic health. While physical activity ameliorates several of the negative effects, loss of ovarian function is associated with decreased physical activity levels. It has been proposed that the changes in brain neurochemical levels and /or impaired skeletal muscle function may underlie this phenomenon.

Methods

We studied the effect of estrogen deficiency induced via ovariectomy (OVX) in female Wistar rats (n = 64). Rats underwent either sham or OVX surgery and were allocated thereafter into four groups matched for body mass and maximal running capacity: sham/control, sham/max, OVX/control, and OVX/max, of which the max groups had maximal running test before euthanasia to induce acute response to exercise. Metabolism, spontaneous activity, and maximal running capacity were measured before (PRE) and after (POST) the surgeries. Three months following the surgery, rats were euthanized, and blood and tissue samples harvested. Proteins were analyzed from gastrocnemius muscle and retroperitoneal adipose tissue via Western blot. Brain neurochemical markers were measured from nucleus accumbens (NA) and hippocampus (HC) using ultra-high performance liquid chromatography.

Results

OVX had lower basal energy expenditure and higher body mass and retroperitoneal adipose tissue mass compared with sham group (p ≤ 0.005). OVX reduced maximal running capacity by 17% (p = 0.005) with no changes in muscle mass or phosphorylated form of regulatory light chain (pRLC) in gastrocnemius muscle. OVX was associated with lower serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) level in the NA compared with sham (p = 0.007). In response to acute exercise, OVX was associated with low serotonin level in the HC and high level in the NA (p ≤ 0.024).

Discussion

Our results highlight that OVX reduces maximal running capacity and affects the response of brain neurochemical levels to acute exercise in a brain region-specific manner. These results may offer mechanistic insight into why OVX reduces willingness to exercise.

Revitalizing Ancient Mitochondria with Nano-Strategies: Mitochondria-Remedying Nanodrugs Concentrate on Disease Control

Mitochondria, widely known as the energy factories of eukaryotic cells, have a myriad of vital functions across diverse cellular processes. Dysfunctions within mitochondria serve as catalysts for various diseases, prompting widespread cellular demise. Mounting research on remedying damaged mitochondria indicates that mitochondria constitute a valuable target for therapeutic intervention against diseases. But the less clinical practice and lower recovery rate imply the limitation of traditional drugs, which need a further breakthrough. Nanotechnology has approached favorable regiospecific biodistribution and high efficacy by capitalizing on excellent nanomaterials and targeting drug delivery. Mitochondria-remedying nanodrugs have achieved ideal therapeutic effects. This review elucidates the significance of mitochondria in various cells and organs, while also compiling mortality data for related diseases. Correspondingly, nanodrug-mediate therapeutic strategies and applicable mitochondria-remedying nanodrugs in disease are detailed, with a full understanding of the roles of mitochondria dysfunction and the advantages of nanodrugs. In addition, the future challenges and directions are widely discussed. In conclusion, this review provides comprehensive insights into the design and development of mitochondria-remedying nanodrugs, aiming to help scientists who desire to extend their research fields and engage in this interdisciplinary subject.

Resting energy expenditure based on equation estimation can predict renal outcomes in patients with type 2 diabetes mellitus and biopsy-proven diabetic kidney disease

AIMS

The aim of this study was to investigate the relationship between resting energy expenditure (REE) based on equation estimation and renal outcomes in patients with diabetes kidney disease (DKD).

METHODS

A total of 124 patients were enrolled from a retrospective cohort of Type 2 Diabetes mellitus (T2DM) patients with biopsy-proven DKD. Renal outcome defined as End-Stage Renal Disease (ESRD). To compare the predictive ability of different REE estimation equations on ESRD. Patients' REE was assessed according to the estimating equation with the best predictive power, and then the relationship between REE and ESRD risk was fitted using a restricted cubic spline curve (RCS) plot and REE cutoff values were obtained. Grouping using cutoff values, and ultimately evaluate the relationship between REE and the risk of ESRD using a Multivariate Cox regression model.

RESULTS

The strongest predictive validity for renal outcomes was the NDCKD-equation. The patients were divided into the higher-REE group (n = 78) and the lower-REE group (n = 46), based on the cutoff value. During the follow-up, 30 of 124 patients (24.2%) proceeded to ESRD. Multivariate Cox regression models showed that the risk of ESRD in patients with lower REE was 6.08 times increased compared with that in those with higher REE (HR = 6.08; 95% CI, 1.28-28.80, p = 0.023).

CONCLUSION

These findings suggested that the lower REE was an independent risk factor for unfavorable renal outcomes in patients with DKD.

Age But Not Menopausal Status Is Linked to Lower Resting Energy Expenditure

CONTEXT

It remains uncertain whether aging before late adulthood and menopause are associated with fat-free mass and fat mass-adjusted resting energy expenditure (REEadj).

OBJECTIVES

We investigated whether REEadj differs between middle-aged and younger women and between middle-aged women with different menopausal statuses. We repeated the age group comparison between middle-aged mothers and their daughters to partially control for genotype. We also explored whether serum estradiol and FSH concentrations explain REEadj in midlife.

METHODS

We divided 120 women, including 16 mother-daughter pairs, into age groups; group I (n = 26) consisted of participants aged 17 to 21, group II (n = 35) of those aged 22 to 38, and group III (n = 59) of those aged 41 to 58 years. The women in group III were further categorized as pre- or perimenopausal (n = 19), postmenopausal (n = 30), or postmenopausal hormone therapy users (n = 10). REE was assessed using indirect calorimetry, body composition using dual-energy X-ray absorptiometry, and hormones using immunoassays.

RESULTS

The REEadj of group I was 126 kcal/day [95% confidence interval (CI): 93-160] higher than that of group III, and the REEadj of group II was 88 kcal/day (95% CI: 49-127) higher. Furthermore, daughters had a 100 kcal/day (95% CI: 63-138 kcal/day) higher REEadj than their middle-aged mothers (all P < .001). In group III, REEadj was not lower in postmenopausal women and did not vary by sex hormone concentrations.

CONCLUSIONS

We demonstrated that REEadj declines with age in women before late adulthood, also when controlling partially for genetic background, and that menopause may not contribute to this decline.

Recovery from FOLFOX chemotherapy-induced systemic and skeletal muscle metabolic dysfunction in mice

FOLFOX (5-fluorouracil, leucovorin, oxaliplatin) chemotherapy is used to treat colorectal cancer and can acutely induce metabolic dysfunction. However, the lasting effects on systemic and skeletal muscle metabolism after treatment cessation are poorly understood. Therefore, we investigated the acute and lasting effects of FOLFOX chemotherapy on systemic and skeletal muscle metabolism in mice. Direct effects of FOLFOX in cultured myotubes were also investigated. Male C57BL/6J mice completed four cycles (acute) of FOLFOX or PBS. Subsets were allowed to recover for 4 wk or 10 wk. Comprehensive Laboratory Animal Monitoring System (CLAMS) metabolic measurements were performed for 5 days before study endpoint. C2C12 myotubes were treated with FOLFOX for 24 hr. Acute FOLFOX attenuated body mass and body fat accretion independent of food intake or cage activity. Acute FOLFOX decreased blood glucose, oxygen consumption (V̇o2), carbon dioxide production (V̇co2), energy expenditure, and carbohydrate (CHO) oxidation. Deficits in V̇o2 and energy expenditure remained at 10 wk. CHO oxidation remained disrupted at 4 wk but returned to control levels after 10 wk. Acute FOLFOX reduced muscle COXIV enzyme activity, AMPK(T172), ULK1(S555), and LC3BII protein expression. Muscle LC3BII/I ratio was associated with altered CHO oxidation (r = 0.75, P = 0.03). In vitro, FOLFOX suppressed myotube AMPK(T172), ULK1(S555), and autophagy flux. Recovery for 4 wk normalized skeletal muscle AMPK and ULK1 phosphorylation. Our results provide evidence that FOLFOX disrupts systemic metabolism, which is not readily recoverable after treatment cessation. FOLFOX effects on skeletal muscle metabolic signaling did recover. Further investigations are warranted to prevent and treat FOLFOX-induced metabolic toxicities that negatively impact survival and life quality of patients with cancer.NEW & NOTEWORTHY The present study demonstrates that FOLFOX chemotherapy induces long-lasting deficits in systemic metabolism. Interestingly, FOLFOX modestly suppressed skeletal muscle AMPK and autophagy signaling in vivo and in vitro. The FOLFOX-induced suppression of muscle metabolic signaling recovered after treatment cessation, independent of systemic metabolic dysfunction. Future research should investigate if activating AMPK during treatment can prevent long-term toxicities to improve health and quality of life of patients with cancer and survivors.

The importance of fat-free mass and constituent tissue-organs in the control of human appetite

PURPOSE OF REVIEW

Traditional models of human appetite focus on the contribution of adipose tissue and the gastrointestinal tract, both of which exert mainly inhibitory influences. The purpose of this review is to consider the biological factors that influence the drive to eat.

RECENT FINDINGS

Fat-free mass is positively associated with objectively measured meal size and daily energy intake. These findings have been replicated in multiple populations across the life-course in laboratory and free-living studies. Studies have shown that the effect of fat-free mass is statistically mediated by resting metabolic rate, suggesting that energy expenditure per se may influence energy intake. A recent MRI study has reported that fasting hunger was associated with high metabolic rate organ (heart, liver, brain, kidneys) and skeletal muscle mass. Integrating measures of body composition at the tissue-organ level and markers of their metabolic function with appetitive measures could provide novel insight into the mechanisms that influence appetite.

SUMMARY

These recent findings suggest that fat-free mass and resting metabolic rate are determinants of energy intake. Consideration of fat-free mass and energy expenditure as physiological sources of appetitive signals helps reconcile the mechanisms underpinning the inhibition of eating with those that drive eating.

Reliability of resting metabolic rate between and within day measurements using the Vyntus CPX system and comparison against predictive formulas

Background: To detect longitudinal changes of resting metabolic rate (RMR) resulting from the effects of energetic stress, reliable RMR measurements are crucial. The Vyntus CPX is a new automated indirect calorimetry system for which RMR reliability has not been determined. Additionally, its agreement with common predictive RMR formulas is unknown. Aim: To determine the within and between-day reliability of RMR measurements using the Vyntus CPX system and its agreement with predictive RMR formulas. Methods: Young (31  ±  7 years) healthy participants (n = 26, 12 females, 14 males) completed three measurements of RMR, two consecutive measures on the same day, one the day before/after, all under standardised conditions. Reliability was assessed with pairwise comparisons of between-day at the same time (BDST), within day consecutive measurements (WDCM) and between-day different time (BDDT), for parameters of reliability (mean change (MC), intraclass correlation (ICC) and typical error of measurement (TEM)). Measured RMR values (kcal/day) were compared against predictive values of 4 common formulas. Results: Parameters of reliability (mean, (95% confidence interval)) were: -BDST: MC, 0.2(-2.3-2.7)% (p = 0.67); ICC, 0.92(0.84-0.97); TEM, 4.5(3.5-6.2)%. -WDCM: MC, -2.5(-6.2-1.3)% (p = 0.21); ICC, 0.88(0.74-0.88); TEM, 7.0(5.4-9.8)%. -BDDT: MC, -1.5(-4.8-1.9)% (p = 0.57); ICC, 0.90(0.76-0.95); TEM, 6.1(4.8-8.5)%. RMR_ratios (measured/predicted) were: 1.04  ±  0.14 (Nelson, p = 0.13), 1.03  ±  0.10 (Mifflin, p = 0.21), 0.98  ±  0.09 (Harris-benedict, p = 0.30), 0.95  ±  0.11 (Cunningham₁₉₈₀, p = 0.01), 1.00  ±  0.12 (Cunningham₁₉₉₁, p = 0.90) and 0.96  ±  0.13 (DXA, p = 0.03). Conclusions: The Vyntus CPX is reliable and measured RMR values agreed with four predictive formulas but are lower than Cunningham₁₉₈₀ and DXA RMR estimates for this population.

Resting and exercise metabolic characteristics in obese children with insulin resistance

Purpose: This study aimed to explore the characteristics of resting energy expenditure (REE) and lipid metabolism during incremental load exercise in obese children and adolescents with insulin resistance (IR) to provide evidence for exercise intervention in obese children and adolescents with IR.

Method: From July 2019 to August 2021, 195 obese children and adolescents aged 13–17 were recruited through a summer camp. The participants were divided into IR (n = 67) and no-IR (without insulin resistance, n = 128) groups and underwent morphology, blood indicators, body composition, and resting energy consumption gas metabolism tests. Thirty participants each were randomly selected from the IR and no-IR groups to carry out the incremental treadmill test.

Results: Significant metabolic differences in resting and exercise duration were found between the IR and no-IR groups. In the resting state, the resting metabolic equivalents (4.33 ± 0.94 ml/min/kg vs. 3.91 ± 0.73 ml/min/kg, p = 0.001) and REE (2464.03 ± 462.29 kcal/d vs. 2143.88 ± 380.07 kcal/d, p &lt; 0.001) in the IR group were significantly higher than in the no-IR group. During exercise, the absolute maximal fat oxidation (0.33 ± 0.07 g/min vs. 0.36 ± 0.09 g/min, p = 0.002) in the IR group was significantly lower than in the no-IR group; maximal fat oxidation intensity (130.9 ± 8.9 bpm vs. 139.9 ± 7.4 bpm, p = 0.040) was significantly lower in the IR group.

Conclusion: Significant resting and exercise metabolic differences were found between obese IR and no-IR children and adolescents. Obese IR children and adolescents have higher REE and lower maximal fat oxidation intensity than obese no-IR children and adolescents.

Rates of protein synthesis are maintained in brain but reduced in skeletal muscle during dietary sulfur amino acid restriction

Dietary interventions such as sulfur amino acid restriction (SAAR) target multiple drivers of aging, and show promise for preventing or delaying the onset of chronic diseases. SAAR promotes metabolic health and longevity in laboratory animals. The effects of SAAR on proteostasis remain relatively unexplored. We previously reported that SAAR promotes mitochondrial proteostatic maintenance, despite suppression of global protein synthesis, in two peripheral tissues, the liver and skeletal muscle. However, the brain, a tissue vulnerable to age-related neurodegenerative diseases due to the loss of proteostasis, has not been thoroughly studied. Therefore, we sought to reveal proteostatic responses in the brains of mice fed SAAR for 35 days. Here, we demonstrate that male C57Bl/6J mice fed two levels of SAAR maintained rates of protein synthesis in all sub-cellular fractions of the pre-frontal cortex. In comparison, rates of skeletal muscle protein synthesis in SAAR fed mice were slower than control-fed mice. To gain mechanistic insight, we examined several key nutrient/energy sensitive signaling proteins: AMP-activated protein kinase (AMPK), eukaryotic initiation factor 2 (eIF2), and ribosomal protein S6 (rpS6). SAAR had minimal to modest effects on the total abundance and phosphorylation of these proteins in both tissues. Our results indicate that the pre-frontal cortex in brain is resistant to perturbations in protein synthesis in mice fed SAAR, unlike skeletal muscle, which had a reduction in global protein synthesis. The results from this study demonstrate that proteostatic control in brain is of higher priority than skeletal muscle during dietary SAAR.

Phenotypic differences between people varying in muscularity

BACKGROUND

Body mass is the primary metabolic compartment related to a vast number of clinical indices and predictions. The extent to which skeletal muscle (SM), a major body mass component, varies between people of the same sex, weight, height, and age is largely unknown. The current study aimed to explore the magnitude of muscularity variation present in adults and to examine if variation in muscularity associates with other body composition and metabolic measures.

METHODS

Muscularity was defined as the difference (residual) between a person's actual and model-predicted SM mass after controlling for their weight, height, and age. SM prediction models were developed using data from a convenience sample of 492 healthy non-Hispanic (NH) White adults (ages 18-80 years) who had total body SM and SM surrogate, appendicular lean soft tissue (ALST), measured with magnetic resonance imaging and dual-energy X-ray absorptiometry, respectively; residual SM (SM_R ) and ALST were expressed in kilograms and kilograms per square meter. ALST mass was also evaluated in a population sample of 8623 NH-White adults in the 1999-2006 National Health and Nutrition Examination Survey. Associations between muscularity and variation in the residual mass of other major organs and tissues and resting energy expenditure were evaluated in the convenience sample.

RESULTS

The SM, on average, constituted the largest fraction of body weight in men and women up to respective BMIs of 35 and 25 kg/m² . SM in the convenience sample varied widely with a median of 31.2 kg and an SM_R inter-quartile range/min/max of 3.35 kg/-10.1 kg/9.0 kg in men and 21.1 kg and 2.59 kg/-7.2 kg/7.5 kg in women; per cent of body weight as SM at 25th and 75th percentiles for men were 33.1% and 39.6%; corresponding values in women were 24.2% and 30.8%; results were similar for SM_R indices and for ALST measures in the convenience and population samples. Greater muscularity in the convenience sample was accompanied by a smaller waist circumference (men/women: P < 0.001/=0.085) and visceral adipose tissue (P = 0.014/0.599), larger liver (P = 0.065/<0.001), kidneys (P = 0.051/<0.009), and bone mineral (P < 0.001/<0.001), and larger magnitude resting energy expenditure (P < 0.001/<0.001) than predicted for the same sex, age, weight, and height.

CONCLUSIONS

Muscle mass is the largest body compartment in most adults without obesity and is widely variable in mass across people of similar body size and age; and high muscularity is accompanied by distinct body composition and metabolic characteristics. This previously unrecognized heterogeneity in muscularity in the general population has important clinical and research implications.

Association of Serum Adipokines and Resting Energy Expenditure in Patients With Chronic Kidney Disease

Background and Aim

Metabolic disorders are prevalent in patients with chronic kidney disease (CKD) and may lead to protein energy wasting (PEW). Adipokines improve connections between PEW and energy metabolism. We aimed to determine the relationship between adipokine levels and resting energy expenditure (REE) in patients with CKD.

Methods

A total of 208 patients in non-dialyzed CKD stages 3–5 were enrolled in this cross-sectional study. Serum adipokines (leptin, adiponectin, and interleukin 6 (IL-6) were measured using enzyme-linked immunosorbent assay. Patient's REE was measured using indirect calorimetry. Fat mass (FM) and lean tissue mass (LTM) were measured using multiple-frequency bioimpedance analysis. Spearman correlation analyses and multivariate linear regression models were used to assess the association between serum adipokines and REE.

Results

The mean age was 52.7 ± 14.6 years, and 26.9, 26.4, and 46.7% of our participants had CKD stages 3, 4, and 5, respectively. The median values of serum adiponectin, leptin, and IL-6 were 470.4 (range, 291.1–802.2), 238.1 (range, 187.9–418.4), and 4.0 (range, 2.4–9.5) pg/mL, respectively. The male participants had significantly lower FM% (P = 0.001) and lower leptin levels (P < 0.001) than the female participants. After adjusting for age, diabetes, high-sensitivity C-reactive protein, intact parathyroid hormone, LTM, and FM, multiple linear regression analysis revealed that serum leptin levels were significantly positively associated with REE in men rather than in women (P < 0.05). Serum adiponectin levels were inversely associated with REE in men, but this association disappeared while FM was additionally adjusted. Adiponectin levels in women were not correlated with REE (P > 0.05). IL-6 was not significantly associated with REE in either men or women.

Conclusions

A sex-specific relationship between serum adipokines (leptin and adiponectin) and REE was observed in patients with CKD stages 3–5, which was partly confounded by FM.

Are metabolic adaptations to weight changes an artefact?

BACKGROUND

Adaptive thermogenesis (AT) is currently defined as the fat-free mass (FFM)-independent change in resting energy expenditure (REE) in response to caloric restriction (CR) or overfeeding (OF). So far, the impact of changes in the anatomical and molecular composition of FFM on AT has not been addressed.

OBJECTIVES

To assess the impact of changes in FFM composition on AT.

METHODS

FFM was assessed in 32 healthy young men during controlled 21-d CR and 14 d of subsequent OF. Anatomical (i.e., the organ/tissue level) and molecular (i.e., water, mineral, and protein content and thus body density) composition of FFM were characterized. REE was measured by indirect calorimetry.

RESULTS

With CR, body weight and REE decreased by 4.2 ± 0.9 kg and 173 ± 107 kcal/d, respectively, with corresponding increases of 3.5 ± 1.2 kg and 194 ± 110 kcal/d during OF (P < 0.001 for all changes). Changes in FFM explained 56.7% and 66.7% of weight loss and weight gain, respectively. Weight changes were associated with changes in various anatomical (i.e., masses of skeletal muscle, liver, kidneys, and brain) and molecular components (total body water, protein, and bone minerals) of FFM. After adjustments for changes in FFM only, AT was 116 ± 127 (P < 0.001) and 27 ± 115 kcal/d (NS) with CR and OF, respectively. Adjustments for FFM and its anatomical and molecular composition reduced AT in response to CR to 83 ± 116 and 122 ± 123 kcal/d (P < 0.05 and P < 0.001) whereas during OF, AT became significant at 87 ± 146 kcal/d (anatomical; P < 0.05) and 86 ± 118 kcal/d (molecular; P < 0.001).

CONCLUSIONS

Adjusting changes in REE with under- and overfeeding for the corresponding changes in the anatomical and molecular composition of FFM decreased AT after CR and increased AT after OF, but overall adjusted AT was likely not large enough in magnitude to be able to prevent weight loss or resist weight gain.