Issues in Measuring and Interpreting Energy Balance and Its Contribution to Obesity

Effects of ketone bodies on energy expenditure, substrate utilization, and energy intake in humans

The potential of ketogenic approaches to regulate energy balance has recently gained attention since ketones may influence both energy expenditure and energy intake. In this narrative review, we summarized the most relevant evidence about the role of ketosis on energy expenditure, substrate utilization, and energy intake in humans. We considered different strategies to induce ketosis, such as fasting, dietary manipulation, and exogenous ketone sources. In general, ketosis does not have a major influence on energy expenditure but promotes a shift in substrate utilization towards ketone body oxidation. The strategies to induce ketosis by reduction of dietary carbohydrate availability (e.g., ketogenic diets) do not independently influence energy intake, being thus equally effective for weight loss as diets with higher carbohydrate content. In contrast, the intake of medium-chain triglycerides and ketone esters induces ketosis and appears to increase energy expenditure and reduce energy intake in the context of high carbohydrate availability. These latter strategies lead to slightly enhanced weight loss. Unfortunately, distinguishing the effects of the various ketogenic strategies per se from the effects of other physiological responses is not possible with the available human data. Highly controlled, inpatient studies using targeted strategies to isolate the independent effects of ketones are required to adequately address this knowledge gap.

Prevalence of non-alcoholic fatty liver disease and its association with lifestyle habits in adults in Chile: a cross-sectional study from the National Health Survey 2016-2017

Non-alcoholic fatty liver disease (NAFLD) represents an excessive fat accumulation within the liver, usually associated with excess body weight. A liver biopsy is the gold standard for diagnosis, but it is inapplicable in population-based studies. In large populations, non-invasive methods could be used, which may also serve to identify potential protective factors. We aimed to (a) estimate NAFLD prevalence in the adult population in Chile by using non-invasive methods and (b) determine the association between the presence of NAFLD and lifestyle habits. The National Health Survey of Chile 2016–2017 was analysed. We included individuals aged 21–75 years, without infectious diseases nor risky alcohol consumption. NAFLD was detected by either fatty liver index (FLI; considers circulating TAG, circulating γ-glutamyl-transferase, BMI and waist circumference), lipid accumulation product (LAP; considers sex, circulating TAG and waist circumference) or their combination. Lifestyle habits were determined by questionnaires. We included 2774 participants, representative of 10 599 094 (9 831 644, 11 366 544) adults in Chile. NAFLD prevalence (95 % CI) was 39·4 % (36·2, 42·8) by FLI, 27·2 % (24·2, 30·4) by LAP and 23·5 % (20·7, 26·5) by their combination. The prevalence progressively increased with increasing BMI. Of note, less smoking and more moderate-vigorous physical activity and whole-grain consumption were associated with lower odds of having NAFLD, independently of BMI. At least one out of four adults in Chile is afflicted with NAFLD. Health promotion strategies focused on controlling excess body weight and promoting specific lifestyle habits are urgently required.

Time reallocation of physical behaviors induced by endurance exercise in physically active individuals

ABSTRACT

Increasing moderate-vigorous physical activity (MVPA) through exercise requires reallocating time from other physical behavior(s). We aimed to determine the reallocations induced by endurance exercise in physically active individuals. We also searched for behavioral compensatory responses, and explored the effect of exercise on daily energy expenditure. Fourteen participants (8 women; median age 37.8 [IQR 29.9–48.5] yr) exercised on Monday, Wednesday, and Friday mornings (cycling MVPA, 65 min/session; "exercise days"), and avoided exercising on Tuesday and Thursday ("rest days"). Time spent on sleep, sedentary behavior, light-intensity physical activity, and MVPA was determined each day by accelerometers and logs. An energy expenditure index was computed considering minutes spent on each behavior and fixed metabolic equivalents. We found that all participants had lower sleep and higher total (including exercise) MVPA on exercise days compared to rest days. Thus, on exercise vs. rest days, sleep was lower (490 [453–553] vs. 553 [497–599] min/day, respectively, P<0.001), and total MVPA was higher (86 [80–101] vs. 23 [15–45] min/day, respectively; P<0.001). No differences in other physical behaviors were detected. Notably, exercise not only induced reallocations (i.e. less time in other behaviors) but also behavioral compensatory responses in some participants (e.g. increased sedentary behavior). This rearrangement of physical behaviors manifested in exercise-induced increases in energy expenditure from 96 to 232 MET×min/day. In conclusion, active individuals reallocated time from sleep to accommodate morning exercise. Yet exercise induced variable rearrangements of behaviors, with some individuals manifesting compensatory responses. Understanding individual rearrangements may help improve exercise interventions.

Intrinsic cardiorespiratory fitness modulates clinical and molecular response to caloric restriction

OBJECTIVE

Caloric restriction (CR) is one extrinsic intervention that can improve metabolic health, and it shares many phenotypical parallels with intrinsic high cardiorespiratory fitness (CRF), including reduced adiposity, increased cardiometabolic health, and increased longevity. CRF is a highly heritable trait in humans and has been established in a genetic rat model selectively bred for high (HCR) and low (LCR) CRF, in which the HCR live longer and have reduced body weight compared to LCR. This study addresses whether the inherited high CRF phenotype occurs through similar mechanisms by which CR promotes health and longevity.

METHODS

We compared HCR and LCR male rats fed ad libitum (AL) or calorically restricted (CR) for multiple physiological, metabolic, and molecular traits, including running capacity at 2, 8, and 12 months; per-hour metabolic cage activity over daily cycles at 6 and 12 months; and plasma lipidomics, liver and muscle transcriptomics, and body composition after 12 months of treatment.

RESULTS

LCR-CR developed a physiological profile that mirrors the high-CRF phenotype in HCR-AL, including reduced adiposity and increased insulin sensitivity. HCR show higher spontaneous activity than LCR. Temporal modeling of hourly energy expenditure (EE) dynamics during the day, adjusted for body weight and hourly activity levels, suggest that CR has an EE-suppressing effect, and high-CRF has an EE-enhancing effect. Pathway analysis of gene transcripts indicates that HCR and LCR both show a response to CR that is similar in the muscle and different in the liver.

CONCLUSIONS

CR provides LCR a health-associated positive effect on physiological parameters that strongly resemble HCR. Analysis of whole-body EE and transcriptomics suggests that HCR and LCR show line-dependent responses to CR that may be accreditable to difference in genetic makeup. The results do not preclude the possibility that CRF and CR pathways may converge.

Finding balance: understanding the energetics of time-restricted feeding in mice

Over the course of mammalian evolution, the ability to store energy likely conferred a survival advantage when food became scarce. A long-term increase in energy storage results from an imbalance between energy intake and energy expenditure, two tightly regulated parameters that generally balance out to maintain a fairly stable body weight. Understanding the molecular determinants of this feat likely holds the key to new therapeutic development to manage obesity and associated metabolic dysfunctions. Time-restricted feeding (TRF), a dietary intervention that limits feeding to the active phase, can prevent and treat obesity and metabolic dysfunction in rodents fed a high-fat diet, likely by exerting effects on energetic balance. Even when body weight is lower in mice on active-phase TRF, food intake is generally isocaloric as compared with ad libitum fed controls. This discrepancy between body weight and energy intake led to the hypothesis that energy expenditure is increased during TRF. However, at present, there is no consensus in the literature as to how TRF affects energy expenditure and energy balance as a whole, and the mechanisms behind metabolic adaptation under TRF are unknown. This review examines our current understanding of energy balance on TRF in rodents and provides a framework for future studies to evaluate the energetics of TRF and its molecular determinants.

Reproducibility of the energy metabolism response to an oral glucose tolerance test: influence of a postcalorimetric correction procedure

PURPOSE

Metabolic flexibility (MetF), which is a surrogate of metabolic health, can be assessed by the change in the respiratory exchange ratio (RER) in response to an oral glucose tolerance test (OGTT). We aimed to determine the day-to-day reproducibility of the energy expenditure (EE) and RER response to an OGTT, and whether a simulation-based postcalorimetric correction of metabolic cart readouts improves day-to-day reproducibility.

METHODS

The EE was assessed (12 young adults, 6 women, 27 ± 2 years old) using an Omnical metabolic cart (Maastricht Instruments, Maastricht, The Netherlands) after an overnight fast (12 h) and after a 75-g oral glucose dose on 2 separate days (48 h). On both days, we assessed EE in 7 periods (one 30-min baseline and six 15-min postprandial). The ICcE was performed immediately after each recording period, and capillary glucose concentration (using a digital glucometer) was determined.

RESULTS

We observed a high day-to-day reproducibility for the assessed RER (coefficients of variation [CV] < 4%) and EE (CVs < 9%) in the 7 different periods. In contrast, the RER and EE areas under the curve showed a low day-to-day reproducibility (CV = 22% and 56%, respectively). Contrary to our expectations, the postcalorimetric correction procedure did not influence the day-to-day reproducibility of the energy metabolism response, possibly because the Omnical's accuracy was ~ 100%.

CONCLUSION

Our study demonstrates that the energy metabolism response to an OGTT is poorly reproducible (CVs > 20%) even using a very accurate metabolic cart. Furthermore, the postcalorimetric correction procedure did not influence the day-to-day reproducibility. Trial registration NCT04320433; March 25, 2020.

Associations between Intra-Assessment Resting Metabolic Rate Variability and Health-Related Factors

In humans, the variation in resting metabolic rate (RMR) might be associated with health-related factors, as suggested by previous studies. This study explored whether the intra-assessment RMR variability (expressed as a coefficient of variation (CV; %)) is similar in men and women and if it is similarly associated with diverse health-related factors. The RMR of 107 young, and relatively healthy adults, was assessed using indirect calorimetry. Then, the CV for volumes of oxygen consumption (VO2) and carbon dioxide production (VCO2), respiratory exchange ratio (RER), and resting energy expenditure (REE) were computed as indicators of intra-assessment RMR variability. Body composition, cardiorespiratory fitness (peak VO2 uptake), circulating cardiometabolic risk factors, and heart rate and its variability (HR and HRV) were assessed. Men presented higher CVs for VO2, VCO2, and REE (all p ≤ 0.001) compared to women. Furthermore, in men, the intra-assessment RER variability was associated with vagal-related HRV parameters and with mean HR (standardized β = −0.36, −0.38, and 0.41, respectively; all p < 0.04). In contrast, no associations were observed in women. In conclusion, men exhibited higher variability (CVs for VO2, VCO2, and REE) compared to women. The CV for RER could be a potential marker of cardiometabolic risk in young men.

Work/household, transport, and leisure domains account for the sex gap in physical activity in Chile

Background

Women usually have lower levels of moderate-vigorous physical activity (MVPA) than men. This sex gap can be accounted for by differences in MVPA in the work/household, transport, and/or leisure domains. Identifying where the differences lay in a context-specific manner may help close the gap. We aimed to compare MVPA by domain, and the relative contribution of each domain to total MVPA, between men and women in Chile.

Methods

We analyzed the cross-sectional National Health Survey of Chile 2016-2017 (n = 5,056, 64% women, ≥18 years old). MVPA was estimated with the Global Physical Activity Questionnaire. MVPA was expressed in MET × min/week, and the relative contribution to total MVPA by each domain was expressed as percentage. Analyses were conducted including all participants, and also including participants reporting >0 MET × min/week of MVPA (relative contributions can only be computed in the latter).

Results

Including all participants, women (vs. men) had lower MVPA (median [25-75th percentile]) for work/household (0 [0-960] vs. 0 [0-5,760] MET × min/week), for transport (360 [0-1,200] vs. 600 [0-1,680] MET × min/week), and for leisure domains (0 [0-0] vs. 0 [0-480] MET × min/week). Including only participants with >0 MET × min/week of MVPA, women (vs. men) had lower mean relative contributions to total MVPA from work/household (31.3 vs. 35.9%) and leisure domains (10.8 vs. 16.3%, respectively), but higher from the transport domain (57.9 vs. 47.8%).

Conclusion

In Chile, differences in all physical activity domains account for the sex gap in MVPA. Strategies to break job stereotypes, increase opportunities for leisure, and ease active transport are required to encourage MVPA in women.

Predictive equations for energy expenditure in adult humans: From resting to free-living conditions

Humans acquire energy from the environment for survival. A central question for nutritional sciences is how much energy is required to sustain cellular work while maintaining an adequate body mass. Because human energy balance is not exempt from thermodynamic principles, the energy requirement can be approached from the energy expenditure. Conceptual and technological advances have allowed understanding of the physiological determinants of energy expenditure. Body mass, sex, and age are the main factors determining energy expenditure. These factors constitute the basis for predictive equations for resting (REE) and total (TEE) energy expenditure in healthy adults. These equations yield predictions that differ up to ~400 kcal/d for REE and ~550 kcal/d for TEE. Identifying additional factors accounting for such variability and the most valid equations appears relevant. This review used novel approaches based on mathematical modeling of REE and analyses of the data from which REE predictive equations were generated. As for TEE, R² and SE were considered because only a few predictive equations are available. From these analyses, Oxford's and Plucker's equations appear valid for predicting REE and TEE in adults, respectively.

Metabolic health and its association with lifestyle habits according to nutritional status in Chile: A cross-sectional study from the National Health Survey 2016-2017

BACKGROUND

Lifestyle habits associate with metabolic health in overall populations. Whether such association is similar among subjects with a different nutritional status has been less studied. We aimed to (i) determine the prevalence of metabolic phenotypes in Chile, and (ii) determine the association between lifestyle habits and metabolic health according to the nutritional status.

METHODS

The National Health Survey of Chile 2016-2017 was analyzed. A metabolically unhealthy phenotype was defined as manifesting ≥3 of the following risk factors: elevated blood pressure, elevated triglycerides, elevated glucose, elevated waist circumference, or reduced high-density lipoprotein cholesterol. Individuals manifesting <2 risk factors were considered as healthy. The nutritional status was defined as normal weight (18.5 to <25 kg/m2), overweight (25 to <30 kg/m2) or obesity (≥30 kg/m2). Questionnaires were used to estimate smoking habits, alcohol intake, sedentary behavior, moderate-vigorous physical activity, fruits/vegetables consumption, and fish/seafood consumption. The association (odds ratio [95%CI]) between lifestyle habits and metabolic health was determined within each nutritional status, adjusting for age, sex, BMI (in kg/m2), and education.

RESULTS

The prevalence of a metabolically unhealthy phenotype was 36% in the overall sample. Such a prevalence was 7%, 33% and 58% among subjects with normal weight, overweight and obesity, respectively. In subjects with normal weight, the highest quartile of fruits/vegetables consumption was associated with reduced odds of having a metabolically unhealthy phenotype (0.09 [0.01-0.48]). In subjects with obesity, the highest quartile of moderate-vigorous physical activity was associated with reduced odds of having a metabolically unhealthy phenotype (0.29 [0.09-0.91]).

CONCLUSION

One third of the Chilean population manifests an unhealthy phenotype. We identified associations between lifestyle habits and metabolic health that are specific to the nutritional status. Thus, emphasizing fruits/vegetables consumption in subjects with normal weight, and physical activity in subjects with obesity, may maximize the benefits of public health interventions.