Physiology of Energy Expenditure in the Weight-Reduced State

The brain-body energy conservation model of aging

Aging involves seemingly paradoxical changes in energy metabolism. Molecular damage accumulation increases cellular energy expenditure, yet whole-body energy expenditure remains stable or decreases with age. We resolve this apparent contradiction by positioning the brain as the mediator and broker in the organismal energy economy. As somatic tissues accumulate damage over time, costly intracellular stress responses are activated, causing aging or senescent cells to secrete cytokines that convey increased cellular energy demand (hypermetabolism) to the brain. To conserve energy in the face of a shrinking energy budget, the brain deploys energy conservation responses, which suppress low-priority processes, producing fatigue, physical inactivity, blunted sensory capacities, immune alterations and endocrine 'deficits'. We term this cascade the brain-body energy conservation (BEC) model of aging. The BEC outlines (1) the energetic cost of cellular aging, (2) how brain perception of senescence-associated hypermetabolism may drive the phenotypic manifestations of aging and (3) energetic principles underlying the modifiability of aging trajectories by stressors and geroscience interventions.

The past, present, and future of behavioral obesity treatment

Over the last century, hundreds of evaluations have been conducted to examine weight-management interventions related to diet, physical activity, and behavior therapy. These investigations have contributed to a growing body of knowledge that has consistently advanced the field of obesity treatment, while also revealing some persistent challenges. This narrative review summarizes key findings from randomized controlled trials conducted in adults that have combined diet, physical activity, and behavior therapy, an approach variously referred to as behavioral treatment, comprehensive lifestyle modification, or intensive lifestyle intervention. The review shows that current behavioral approaches induce average reductions in baseline body weight of 5 to 10% at 6 to 12 months. Such losses have proven effective in reducing the risk of type 2 diabetes in persons with impaired glucose tolerance and in improving other obesity-related complications. These benefits have also been associated with reductions in healthcare costs. Despite these advances, behavioral treatment is challenged by the need for larger losses to achieve optimal improvements in health, by difficulties associated with maintaining weight loss, and by barriers limiting access to treatment. New anti-obesity medications, when combined with behavioral obesity treatment, hold promise of addressing the first two issues.

Dietary sulfur amino acid restriction in humans with overweight and obesity: a translational randomized controlled trial

BACKGROUND

Dietary sulfur amino acid restriction (SAAR) improves metabolic health in animals. In this study, we investigated the effect of dietary SAAR on body weight, body composition, resting metabolic rate, gene expression profiles in white adipose tissue (WAT), and an extensive blood biomarker profile in humans with overweight or obesity.

METHODS

N = 59 participants with overweight or obesity (73% women) were randomized stratified by sex to an 8-week plant-based dietary intervention low (~ 2 g/day, SAAR) or high (~ 5.6 g/day, control group) in sulfur amino acids. The diets were provided in full to the participants, and both investigators and participants were blinded to the intervention. Outcome analyses were performed using linear mixed model regression adjusted for baseline values of the outcome and sex.

RESULTS

SAAR led to a ~ 20% greater weight loss compared to controls (β 95% CI - 1.14 (- 2.04, - 0.25) kg, p = 0.013). Despite greater weight loss, resting metabolic rate remained similar between groups. Furthermore, SAAR decreased serum leptin, and increased ketone bodies compared to controls. In WAT, 20 genes were upregulated whereas 24 genes were downregulated (FDR < 5%) in the SAAR group compared to controls. Generally applicable gene set enrichment analyses revealed that processes associated with ribosomes were upregulated, whereas processes related to structural components were downregulated.

CONCLUSION

Our study shows that SAAR leads to greater weight loss, decreased leptin and increased ketone bodies compared to controls. Further research on SAAR is needed to investigate the therapeutic potential for metabolic conditions in humans.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT04701346, registered Jan 8th 2021, https://www.

CLINICALTRIALS

gov/study/NCT04701346.

Giving weight to incretin-based pharmacotherapy for obesity-related sleep apnea: a revolution or a pipe dream?

Obesity is a chronic disease affecting over 670 million adults globally, with multiple complications including obstructive sleep apnea (OSA). Substantial weight loss in patients with obesity-related OSA can reduce or even eliminate OSA as well as reduce sleepiness and improve cardio-metabolic health. Evidence suggests that these improvements exceed those that occur with device-based OSA therapies like continuous positive airway pressure which continue to be the first-line of therapy. Resistance to weight management as a first-line strategy to combat OSA could arise from the complexities in delivering and maintaining adequate weight management, particularly in sleep clinic settings. Recently, incretin-based pharmacotherapies including glucagon-like peptide 1 (GLP-1) receptor agonists alone or combined with glucose-dependent insulinotropic polypeptide (GIP) receptor agonists have been developed to target glycemic control in type 2 diabetes. These medications also slow gastric emptying and reduce energy intake. In randomized, placebo-controlled trials of these medications in diabetic and non-diabetic populations with obesity, participants on active medication lost up to 20% of their body weight, with corresponding improvements in blood pressure, lipid levels, physical functioning, and fat mass loss. Their adverse effects are predominantly gastrointestinal-related, mild, and transient. There are trials currently underway within individuals with obesity-related OSA, with a focus on reduction in weight, OSA severity, and cardio-metabolic outcomes. These medications have the potential to substantially disrupt the management of OSA. Pending coming data, we will need to consider pharmacological weight loss as a first-line therapy and how that influences training and management guidelines.

Mapping the complexities of Relative Energy Deficiency in Sport (REDs): development of a physiological model by a subgroup of the International Olympic Committee (IOC) Consensus on REDs

The 2023 International Olympic Committee (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs) notes that exposure to low energy availability (LEA) exists on a continuum between adaptable and problematic LEA, with a range of potential effects on both health and performance. However, there is variability in the outcomes of LEA exposure between and among individuals as well as the specific manifestations of REDs. We outline a framework for a 'systems biology' examination of the effect of LEA on individual body systems, with the eventual goal of creating an integrated map of body system interactions. We provide a template that systematically identifies characteristics of LEA exposure (eg, magnitude, duration, origin) and a variety of moderating factors (eg, medical history, diet and training characteristics) that could exacerbate or attenuate the type and severity of impairments to health and performance faced by an individual athlete. The REDs Physiological Model may assist the diagnosis of underlying causes of problems associated with LEA, with a personalised and nuanced treatment plan promoting compliance and treatment efficacy. It could also be used in the strategic prevention of REDs by drawing attention to scenarios of LEA in which impairments of health and performance are most likely, based on knowledge of the characteristics of the LEA exposure or moderating factors that may increase the risk of harmful outcomes. We challenge researchers and practitioners to create a unifying and dynamic physiological model for each body system that can be continuously updated and mapped as knowledge is gained.

Glucagon-like peptide-1/glucagon receptor agonism associates with reduced metabolic adaptation and higher fat oxidation: A randomized trial

OBJECTIVE

This study tested the hypothesis that treatment with the glucagon-like peptide-1/glucagon receptor agonist SAR425899 would lead to a smaller decrease in sleeping metabolic rate (SMR; kilocalories/day) than expected from the loss of lean and fat mass (metabolic adaptation).

METHODS

This Phase 1b, double-blind, randomized, placebo-controlled study was conducted at two centers in inpatient metabolic wards. Thirty-five healthy males and females with overweight and obesity (age = 36.5 ± 7.1 years) were randomized to a calorie-reduced diet (-1000 kcal/d) and escalating doses (0.06-0.2 mg/d) of SAR425899 (n = 17) or placebo (n = 18) for 19 days. SMR was measured by whole-room calorimetry.

RESULTS

Both groups lost weight (-3.68 ± 1.37 kg placebo; -4.83 ± 1.44 kg SAR425899). Those treated with SAR425899 lost more weight, fat mass, and fat free mass (p < 0.05) owing to a greater achieved energy deficit than planned. The SAR425899 group had a smaller reduction in body composition-adjusted SMR (p = 0.002) as compared with placebo, but not 24-hour energy expenditure. Fat oxidation and ketogenesis increased in both groups, with significantly greater increases with SAR425899 (p < 0.05).

CONCLUSIONS

SAR425899 led to reduced selective metabolic adaptation and increased lipid oxidation, which are believed to be beneficial for weight loss and weight-loss maintenance.

Leptin Increases: Physiological Roles in the Control of Sympathetic Nerve Activity, Energy Balance, and the Hypothalamic-Pituitary-Thyroid Axis

It is well established that decreases in plasma leptin levels, as with fasting, signal starvation and elicit appropriate physiological responses, such as increasing the drive to eat and decreasing energy expenditure. These responses are mediated largely by suppression of the actions of leptin in the hypothalamus, most notably on arcuate nucleus (ArcN) orexigenic neuropeptide Y neurons and anorexic pro-opiomelanocortin neurons. However, the question addressed in this review is whether the effects of increased leptin levels are also significant on the long-term control of energy balance, despite conventional wisdom to the contrary. We focus on leptin's actions (in both lean and obese individuals) to decrease food intake, increase sympathetic nerve activity, and support the hypothalamic-pituitary-thyroid axis, with particular attention to sex differences. We also elaborate on obesity-induced inflammation and its role in the altered actions of leptin during obesity.

The metabolic conditioning of obesity: A review of the pathogenesis of obesity and the epigenetic pathways that "program" obesity from conception

Understanding the developmental origins of health and disease is integral to overcome the global tide of obesity and its metabolic consequences, including atherosclerotic cardiovascular disease, type 2 diabetes, hyperlipidemia, and nonalcoholic fatty liver disease. The rising prevalence of obesity has been attributed, in part, to environmental factors including the globalization of the western diet and unhealthy lifestyle choices. In this review we argue that how and when such exposures come into play from conception significantly impact overall risk of obesity and later health outcomes. While the laws of thermodynamics dictate that obesity is caused by an imbalance between caloric intake and energy expenditure, the drivers of each of these may be laid down before the manifestation of the phenotype. We present evidence over the last half-century that suggests that the temporospatial evolution of obesity from intrauterine life and beyond is, in part, due to the conditioning of physiological processes at critical developmental periods that results in maladaptive responses to obesogenic exposures later in life. We begin the review by introducing studies that describe an association between perinatal factors and later risk of obesity. After a brief discussion of the pathogenesis of obesity, including the systemic regulation of appetite, adiposity, and basal metabolic rate, we delve into the mechanics of how intrauterine, postnatal and early childhood metabolic environments may contribute to adult obesity risk through the process of metabolic conditioning. Finally, we detail the specific epigenetic pathways identified both in preclinical and clinical studies that synergistically "program" obesity.

Acute Effects of Whole-Body Electromyostimulation on Energy Expenditure at Resting and during Uphill Walking in Healthy Young Men

The effects of the different electrical frequencies of whole-body electrical stimulation (WB-EMS) on energy expenditure (EE) and the respiratory exchange ratio (RER) remain poorly understood. This study aimed to determine the effects of different WB-EMS electrical frequencies on EE and the RER during supine resting and uphill walking. A total of 10 healthy and recreationally active men (21.6 ± 3.3 years old) participated in the present study. Participants completed two testing sessions in a randomized order. In each session, a variety of impulse frequencies (1 hertz (Hz), 2 Hz, 4 Hz, 6 Hz, 8 Hz, and 10 Hz) were applied in a randomized order, allowing a 10 min passive recovery between them. Oxygen consumption and carbon dioxide production were measured to calculate EE and the RER. All frequencies increased EE at rest (all p ≤ 0.001), with 4 Hz being the frequency producing the highest increase (Δ = 8.89 ± 1.49 kcal/min), as did 6 Hz (Δ = 8.05 ± 1.52 kcal/min) and 8 Hz (Δ = 7.04 ± 2.16 kcal/min). An increment in the RER at rest was observed with 4 Hz, 6 Hz, 8 Hz and 10 Hz (all p ≤ 0.016), but not with 1 Hz and 2 Hz (p ≥ 0.923). During uphill walking, the frequency that elicited the highest increase in EE was 6 Hz (Δ = 4.87 ± 0.84 kcal/min) compared to the unstimulated condition. None of the impulse frequencies altered the RER during uphill walking. WB-EMS increases EE in healthy young men both during resting and uphill walking.

Ketogenic Diet and Weight Loss: Is There an Effect on Energy Expenditure?

A dysregulation between energy intake (EI) and energy expenditure (EE), the two components of the energy balance equation, is one of the mechanisms responsible for the development of obesity. Conservation of energy equilibrium is deemed a dynamic process and alterations of one component (energy intake or energy expenditure) lead to biological and/or behavioral compensatory changes in the counterpart. The interplay between energy demand and caloric intake appears designed to guarantee an adequate fuel supply in variable life contexts. In the past decades, researchers focused their attention on finding efficient strategies to fight the obesity pandemic. The ketogenic or “keto” diet (KD) gained substantial consideration as a potential weight-loss strategy, whereby the concentration of blood ketones (acetoacetate, 3-β-hydroxybutyrate, and acetone) increases as a result of increased fatty acid breakdown and the activity of ketogenic enzymes. It has been hypothesized that during the first phase of KDs when glucose utilization is still prevalent, an increase in EE may occur, due to increased hepatic oxygen consumption for gluconeogenesis and for triglyceride-fatty acid recycling. Later, a decrease in 24-h EE may ensue due to the slowing of gluconeogenesis and increase in fatty acid oxidation, with a reduction of the respiratory quotient and possibly the direct action of additional hormonal signals.

Effects of Intermittent Fasting on Cardiometabolic Health: An Energy Metabolism Perspective

This review summarizes the effects of different types of intermittent fasting (IF) on human cardiometabolic health, with a focus on energy metabolism. First, we discuss the coordinated metabolic adaptations (energy expenditure, hormonal changes and macronutrient oxidation) occurring during a 72 h fast. We then discuss studies investigating the effects of IF on cardiometabolic health, energy expenditure and substrate oxidation. Finally, we discuss how IF may be optimized by combining it with exercise. In general, IF regimens improve body composition, ectopic fat, and classic cardiometabolic risk factors, as compared to unrestricted eating, especially in metabolically unhealthy participants. However, it is still unclear whether IF provides additional cardiometabolic benefits as compared to continuous daily caloric restriction (CR). Most studies found no additional benefits, yet some preliminary data suggest that IF regimens may provide cardiometabolic benefits in the absence of weight loss. Finally, although IF and continuous daily CR appear to induce similar changes in energy expenditure, IF regimens may differentially affect substrate oxidation, increasing protein and fat oxidation. Future tightly controlled studies are needed to unravel the underlying mechanisms of IF and its role in cardiometabolic health and energy metabolism.

Is Glucagon Receptor Activation the Thermogenic Solution for Treating Obesity?

A major challenge of obesity therapy is to sustain clinically relevant weight loss over time. Achieving this goal likely requires both reducing daily caloric intake and increasing caloric expenditure. Over the past decade, advances in pharmaceutical engineering of ligands targeting G protein-coupled receptors have led to the development of highly effective anorectic agents. These include mono-agonists of the GLP-1R and dual GIPR/GLP-1R co-agonists that have demonstrated substantial weight loss in experimental models and in humans. By contrast, currently, there are no medicines available that effectively augment metabolic rate to promote weight loss. Here, we present evidence indicating that activation of the GCGR may provide a solution to this unmet therapeutic need. In adult humans, GCGR agonism increases energy expenditure to a magnitude sufficient for inducing a negative energy balance. In preclinical studies, the glucagon-GCGR system affects key metabolically relevant organs (including the liver and white and brown adipose tissue) to boost whole-body thermogenic capacity and protect from obesity. Further, activation of the GCGR has been shown to augment both the magnitude and duration of weight loss that is achieved by either selective GLP-1R or dual GIPR/GLP-1R agonism in rodents. Based on the accumulation of such findings, we propose that the thermogenic activity of GCGR agonism will also complement other anti-obesity agents that lower body weight by suppressing appetite.