Brown adipose tissue, or BAT, is often described as the body’s biological furnace. Unlike white adipose tissue, which stores energy in the form of large lipid droplets, brown fat burns energy to generate heat, a process known as thermogenesis. This is accomplished largely through uncoupling protein 1, or UCP1, which short-circuits the mitochondrial proton gradient to release energy as heat rather than storing it as ATP. In humans, BAT activity declines with age and obesity, and reduced BAT function has been linked to impaired postprandial glucose clearance, meaning the body’s ability to handle blood sugar spikes after meals. This connection has fueled interest in BAT activation as a therapeutic target for metabolic disease.

The Zagreb team, led by Nikola Habek and Aleksandra Dugandžić, focused on uroguanylin, a peptide hormone that binds to guanylate cyclase C receptors and has previously been implicated in appetite regulation and gut-brain signaling. Uroguanylin is synthesized as an inactive precursor, proguanylin-like pro-uroguanylin (proUGN), which is then cleaved into its active form. While UGN’s role in the intestine is well characterized, its expression and function within the central nervous system, particularly in relation to thermoregulation, have remained poorly understood. The researchers set out to determine whether brain-derived UGN contributes to the regulation of BAT activity, and whether this contribution differs between the sexes.

To address this question, the team employed a multi-pronged experimental strategy. Brown adipose tissue activity was assessed using infrared thermography in wild-type C57Bl/6NCrl mice and UGN knockout littermates. BAT volume was measured using magnetic resonance imaging, while molecular markers associated with the “browning” of fat tissue were quantified using quantitative polymerase chain reaction. In parallel, the researchers measured proUGN expression in both mouse and human brain tissue using enzyme-linked immunosorbent assay, or ELISA. The inclusion of human tissue added a translational dimension often missing from preclinical metabolic studies.

One of the most striking findings emerged from the human brain analysis. In tissue obtained from human subjects, the researchers observed decreased proUGN expression in several brain regions, specifically the hypothalamus, Brodmann area 10, and Brodmann area 11, but only in male subjects with obesity. No comparable decrease was detected in female brain tissue. The hypothalamus is a well-established hub for autonomic control of BAT thermogenesis, receiving input from hunger and satiety circuits and sending sympathetic signals to brown fat depots via the spinal intermediolateral cell column. Brodmann areas 10 and 11, located in the prefrontal cortex, have been implicated in higher-order regulation of appetite and metabolic control. The male-specific reduction in proUGN in these regions suggests that obesity may disrupt a UGN-dependent pathway in a sexually dimorphic manner.

In mice, the relationship between feeding, brain UGN, and brown fat activation also proved to be sex-dependent. After a meal, brown adipose tissue normally increases its activity as part of diet-induced thermogenesis, helping to dissipate excess energy and support glucose disposal. The researchers found that this postprandial activation of BAT was linked to changes in hypothalamic proUGN expression, but this coupling was observed only in male mice. Female mice did not show the same pattern of hypothalamic proUGN regulation after eating, suggesting that the mechanism linking food intake to BAT activation through brain UGN operates differently, or possibly not at all, in females.

The role of the reproductive cycle added another layer of complexity. In female mice, the effects of centrally applied uroguanylin depended not only on sex but also on the phase of the estrous cycle. This finding is notable because it underscores a methodological concern that has gained increasing attention in neuroscience and metabolic research. Many laboratory studies, particularly those in rodents, historically used only male animals, partly to avoid variability attributed to the estrous cycle. The current study suggests that such variability is not mere noise but reflects genuine physiological regulation that could be clinically relevant for female patients.

The researchers also explored whether a GLP-1 analogue, a class of drugs that has transformed the treatment landscape for obesity and type 2 diabetes through medications such as semaglutide and liraglutide, could modulate brain UGN expression and BAT activity. In young male mice, intranasal administration of a GLP-1 analogue increased brown adipose tissue activity and decreased hypothalamic proUGN expression, but these effects were seen only in males. In both male and female mice, the GLP-1 analogue increased BAT activity, suggesting that GLP-1 receptor agonists engage thermogenic pathways through mechanisms that extend beyond UGN signaling, particularly in females. This observation points toward a completely different mechanism of GLP-1 action in the female brain and may help explain sex-dependent differences in clinical responses to these medications.

Chronic administration of uroguanylin itself produced another intriguing sex difference. When UGN was given repeatedly, postprandial BAT activation increased in both sexes, indicating that the hormone can indeed enhance brown fat thermogenic responses in males and females alike. However, an increase in total brown adipose tissue volume was observed only in male mice. Because BAT volume is a determinant of overall thermogenic and glucose-handling capacity, this finding implies that the long-term metabolic benefits of UGN-based interventions may be structurally different in males and females. In males, UGN appears capable of both activating existing brown fat and expanding the tissue itself, whereas in females, the effect appears limited to functional activation without tissue expansion.

The authors emphasize that the therapeutic implications of these findings are substantial. If brain-derived UGN regulates brown fat in a sex-dependent manner, then any attempt to harness this pathway for the treatment of obesity or type 2 diabetes must account for the patient’s sex. A UGN-based therapy that works well in men might produce blunted or entirely different effects in women, and vice versa. Similarly, the estrous-cycle dependence of UGN’s central effects in females raises the possibility that hormonal status, including menstrual cycle phase, hormonal contraceptive use, or menopause, could influence how women respond to BAT-targeting therapies. This kind of nuance has been historically overlooked in metabolic drug development, where clinical trials often enroll predominantly male participants or fail to stratify results by sex.

The study also raises fundamental questions about the biology of uroguanylin in the central nervous system. The finding that proUGN expression decreases in the hypothalamus and prefrontal cortex of men with obesity suggests that obesity may perturb a brain peptide system that is not typically considered part of the metabolic disease landscape. Whether this reduction is a cause or consequence of obesity, and whether it can be reversed through weight loss or pharmacological intervention, remains to be determined. The mouse data indicating that GLP-1 analogues can modulate hypothalamic proUGN expression adds an additional dimension, suggesting that some of the metabolic benefits of these blockbuster weight-loss drugs could be mediated, at least in part, through UGN-dependent pathways in males.

The Zagreb team’s work fits within a growing body of literature highlighting sex differences in metabolic physiology. Brown adipose tissue itself is known to differ between males and females in humans, with some studies suggesting higher BAT prevalence and activity in women. The neural circuits governing BAT thermogenesis, including hypothalamic and brainstem pathways, are also influenced by gonadal hormones such as estrogen and testosterone. By demonstrating that a specific brain peptide, uroguanylin, participates in this sexual dimorphism, the study provides a concrete molecular handle on a phenomenon that has long been recognized but poorly understood at the mechanistic level.

Looking ahead, the researchers suggest that the development of therapies targeting brain-activated brown fat must incorporate sex as a biological variable from the earliest stages of research and development. As the global burden of obesity and type 2 diabetes continues to grow, and as GLP-1 receptor agonists reshape expectations for pharmacological treatment, understanding the precise neural mechanisms through which these interventions work, and how they differ between men and women, will be critical for optimizing their use. The study by Habek, Ratko, Dugandžić, and colleagues represents an important step in that direction, revealing that one of the brain’s most overlooked peptides may play a central role in determining how our bodies burn the calories we consume.

Brown fat, distinct from white fat, plays a vital role in thermogenesis—the production of heat by burning calories. Historically, mitochondria in brown fat cells have been credited with this heat generation, chiefly through a protein known as uncoupling protein 1 (UCP1). UCP1 facilitates the dissipation of the proton gradient generated during cellular respiration, releasing energy as heat instead of storing it as ATP. This process supports temperature regulation, especially in cold environments, and has been proposed as a target for weight loss since activating brown fat increases energy expenditure.

Surprisingly, earlier studies revealed that brown fat in mice lacking UCP1 still managed to generate heat and consume calories, indicating the presence of yet unidentified “back-up” heat-producing systems. In a recent study published in Nature, the research team led by Dr. Irfan Lodhi unearthed that peroxisomes, organelles involved in lipid metabolism, serve as this critical alternative source of thermogenesis. They demonstrated that peroxisomes in brown fat cells ramp up both in number and metabolic activity when exposed to cold, especially compensating when UCP1-dependent mitochondrial heat production is impaired.

Central to this alternative thermogenic pathway is a peroxisomal enzyme called acyl-CoA oxidase 2 (ACOX2). This enzyme orchestrates the breakdown of branched-chain fatty acids within peroxisomes, a metabolic process that consumes energy and results in heat production. Through genetic manipulation, researchers found that mice deficient in ACOX2 within their brown fat exhibited impaired cold tolerance, reduced heat output, and showed metabolic disturbances such as insulin resistance and a propensity for obesity when subjected to high-fat diets.

Conversely, mice engineered to overexpress ACOX2 in their brown fat displayed a remarkable metabolic advantage. These animals maintained higher body temperatures during cold exposure, demonstrated improved glucose homeostasis, and resisted weight gain even when consuming calorie-dense diets. These findings underscore the functional significance of ACOX2-driven peroxisomal metabolism as a metabolic amplifier capable of enhancing energy expenditure and protecting against diet-induced metabolic dysfunction.

To visualize and quantify these effects at the cellular level, the researchers employed innovative tools including a fluorescent heat sensor that illuminated increased cellular temperatures upon ACOX2-mediated metabolism of specific fatty acid substrates. Complementary infrared thermal imaging corroborated diminished heat generation in mice lacking ACOX2, painting a compelling picture of peroxisomal thermo-metabolic activity’s role in whole-body energy balance.

Intriguingly, the branched fatty acids metabolized by ACOX2 are not exclusive to endogenous synthesis. They are also sourced from dietary components such as dairy products and human breast milk, as well as produced by certain gut microbiota. This raises the tantalizing prospect of nutritional or probiotic interventions tailored to augment this peroxisomal heat-generating pathway. Such strategies could pave the way for non-invasive, accessible therapies aimed at enhancing metabolic rates and mitigating obesity and insulin resistance.

While the current investigations are conducted in murine models, there is mounting evidence supporting the translational relevance of this pathway in humans. Previous epidemiological studies noted a correlation between elevated plasma levels of these branched fatty acids and lower body mass indices among individuals, although causality remains to be definitively established. The research team is actively pursuing clinical studies to test whether dietary supplementation or pharmacological activation of ACOX2 can amplify this metabolic circuitry in people.

The study not only broadens the fundamental understanding of brown fat biology but also challenges the orthodox view that mitochondrial UCP1 activity is the sole driver of thermogenesis in adipose tissue. It highlights peroxisomes as dynamic, energetically significant organelles that contribute critically to systemic energy homeostasis. This dual thermogenic mechanism offers redundancy during cold stress and possibly other metabolic challenges, underscoring the evolutionary importance of maintaining body temperature and metabolic flexibility.

From a therapeutic standpoint, activating ACOX2 presents a promising target for drug development. The authors have filed a provisional patent through Washington University to explore pharmacological means of enhancing ACOX2 activity and thus stimulating peroxisomal heat production. If successful, this approach could complement or even outperform traditional weight-loss methods by harnessing the body’s intrinsic energy-burning capacity with potentially fewer side effects or compliance issues than current treatments.

Ultimately, these findings illuminate a sophisticated metabolic interplay within brown fat that orchestrates the breakdown of specialized fatty acids to generate heat and regulate glucose metabolism. The peroxisomal metabolism pathway adds a vital dimension to the regulation of energy expenditure, making it a compelling focus for future research aimed at tackling the global epidemic of obesity and metabolic disorders. As Dr. Lodhi emphasizes, modulating this pathway may facilitate sustainable weight control and metabolic health, transforming paradigms in obesity management.

This comprehensive investigation marks a significant stride toward leveraging the body’s natural thermogenic machinery to combat metabolic disease. It invites scientists, clinicians, and nutritionists alike to rethink current strategies, consider novel metabolic targets, and embrace an integrated approach incorporating cellular metabolism, dietary factors, and microbial contributions to holistic metabolic wellness.

Subject of Research: Brown adipose tissue thermogenesis and metabolic regulation via peroxisomal metabolism

Article Title: Peroxisomal metabolism of branched fatty acids regulates energy homeostasis

News Publication Date: 17-Sep-2025

Web References: http://dx.doi.org/10.1038/s41586-025-09517-7

References: Liu X, He A, Lu D, Hu D, Tan M, Abere A, Goodarzi P, Ahmad B, Kleiboeker B, Finck BN, Zayed M, Funai K, Brestoff JR, Javaheri A, Weisensee P, Mittendorfer B, Hsu F, Van Veldhoven PP, Razani B, Semenkovich CF, Lodhi IJ. Peroxisomal metabolism of branched fatty acids regulates energy homeostasis. Nature. Sept. 17, 2025. DOI: 10.1038/s41586-025-09517-7.

Image Credits: Weisensee Lab

Keywords: Brown adipose tissue, metabolism, peroxisomes, acyl-CoA oxidase 2, thermogenesis, branched fatty acids, obesity, insulin resistance, energy expenditure

Chronic diseases exacerbated by poor nutrition—including cardiovascular disease, Type 2 diabetes, and obesity—continue to dominate the health landscape, accounting for an overwhelming 90% of the $4.5 trillion annual expenditure on U.S. healthcare. This alarming economic and health impact underscores the urgent need for innovative solutions that transcend conventional pharmacological approaches. The Health Care by Food™ initiative aims to rigorously examine how medically tailored nutrition can serve as an effective therapeutic modality, potentially altering disease trajectories and improving patient outcomes.

The recent wave of funding supports the development of detailed clinical trial protocols that will serve as the foundation for future large-scale randomized controlled trials. These planning grants enable investigators to meticulously design interventions that encompass produce prescriptions, medically tailored groceries, and prepared meals. Central to this research is understanding the mechanisms by which dietary modifications influence disease progression, metabolic parameters, and overall health status in populations with chronic conditions.

Kevin Volpp, M.D., Ph.D., who spearheads the initiative, emphasizes the critical importance of generating data that insurers can rely upon when making coverage determinations. “This program is structured to pinpoint specific features of food is medicine interventions that align with payer priorities, thereby facilitating integration into healthcare reimbursement frameworks,” Volpp explains. With his background in health incentives and behavioral economics, Volpp advocates for harnessing human-centered design principles to enhance patient engagement, adherence, and retention within these programs.

One of the distinctive features of this initiative is its iterative research model which begins with small-scale, human-centered clinical trials focusing on behavioral science aspects. To date, 23 pilot trials are currently underway, each exploring various strategies to optimize program implementation and maximize therapeutic benefit. These foundational studies will generate valuable insights on patient responses and inform the design of robust, scalable interventions suitable for nationwide adoption.

Diet-related chronic diseases are multifactorial in nature, where both biological and socio-environmental factors converge. The Health Care by Food™ initiative appreciates this complexity, incorporating behavioral economics and motivational strategies that address barriers to healthy eating in vulnerable populations. The new grants allow for thorough exploration of intervention mechanisms, ranging from nutrient absorption and metabolic modulation to psychosocial determinants that influence dietary behaviors.

The anticipated large-scale randomized controlled trials will not only elucidate clinical efficacy but will also provide comprehensive cost-effectiveness analyses that are essential for policy advocacy. Such evidence is imperative for validating food as a reimbursable treatment modality, shifting the healthcare paradigm towards prevention and management through nutrition. Researchers funded by this initiative are tasked with constructing rigorous protocols that meet stringent federal funding criteria, facilitating future support from government agencies, industry, and philanthropic organizations.

Beyond the clinical and economic dimensions, Health Care by Food™ is embedded within a broader advocacy and educational framework, aimed at reshaping perceptions around nutrition in medical care. This multifaceted strategy addresses systemic health inequities by promoting equitable access to nutritious foods, thereby advancing social determinants of health. Strategic partnerships with prominent funders—including The Rockefeller Foundation, Kroger, and Kaiser Permanente—reflect a collaborative ecosystem geared towards driving innovation in chronic disease management.

As preliminary data from ongoing trials begin to emerge later this year, the medical community and policymakers alike will gain unprecedented insights into how food-based interventions can be harnessed as standardized components of treatment regimens. This evidence base will be pivotal in establishing food is medicine programs as integral, reimbursable facets of healthcare delivery, with the potential to revolutionize disease prevention and improve population health outcomes on a massive scale.

The scientific rigor underlying this initiative is evident in its commitment to employing advanced research methodologies, comprehensive behavioral assessments, and precise nutritional biochemistry. By focusing on both physiological and psychosocial outcomes, the Health Care by Food™ program exemplifies translational research that bridges bench science with clinical practice, ultimately striving to reduce the burden of cardiovascular and metabolic diseases through targeted dietary therapeutics.

In summary, the American Heart Association’s Health Care by Food™ initiative stands at the forefront of a transformative movement, seeking not merely to supplement medical care with better nutrition but to redefine the concept of treatment itself. By investing in cutting-edge clinical research, fostering interdisciplinary collaboration, and advocating for systematic policy change, the AHA is championing a future where food is recognized as a potent and reimbursable medicine in the battle against chronic disease.

Subject of Research: Integration of Nutrition-Based Interventions into Chronic Disease Management through Clinical Trial Design and Implementation

Article Title: American Heart Association Launches Major Grant Initiative to Propel “Food Is Medicine” Research into Clinical Practice

News Publication Date: May 20, 2025

Web References:

• Health Care by Food™ Initiative: https://healthcarexfood.org/
• AHA Newsroom: https://newsroom.heart.org/news/planning-grants-awarded-for-competitive-proposals-testing-efficacy-of-food-is-medicine?preview=05d2&preview_mode=True#_ftnref1
• AHA Presidential Advisory on Food Is Medicine: https://www.ahajournals.org/doi/full/10.1161/CIR.0000000000001182

References:

• Center for Disease Control. (2024, July). Fast Facts: Health and Economic Costs of Chronic Conditions. U.S. Centers for Disease Control and Prevention.

Keywords:
Health care, nutrition, food is medicine, clinical trials, chronic disease, cardiovascular disease, Type 2 diabetes, obesity, behavioral economics, medical nutrition therapy, health policy, disease prevention

The utilization of GLP-1 receptor agonists, such as semaglutide and liraglutide, has revolutionized the management of type 2 diabetes and provided robust strategies for weight loss. Recently, the approval of tirzepatide, which uniquely combines actions of GLP-1 and GIP, has expanded therapeutic options for both obesity and diabetes management. The clinical community is increasingly focused on understanding not just the efficacy of these drugs in facilitating weight loss, but also their capacity to mitigate losses in lean muscle mass, an important factor for metabolic health and physical functionality. This study offers vital insights into these concerns, thereby enriching the discussion around obesity treatment strategies.

The six-month prospective cohort study enrolled 200 adults aged between 18 to 65 years with a body mass index (BMI) of 25 kg/m² or higher, indicative of overweight or obesity. Participants were divided into two groups, with 120 individuals receiving tirzepatide and 80 individuals receiving semaglutide. In addition to pharmacological intervention, subjects received education on resistance training and dietary protein intake, emphasizing a multifaceted approach to weight management. Standardized education provided by a board-certified obesity physician helped ensure participants were well-equipped to utilize the medications effectively.

To accurately assess body composition changes over the six-month intervention, researchers employed bioelectrical impedance analysis using the InBody 570 system. This advanced body composition analyzer provided comprehensive data on muscle, fat, and water distribution in the participants, allowing for a detailed understanding of shifts in body composition attributable to the management strategies deployed. By measuring parameters such as skeletal muscle mass and body fat percentage, the researchers could glean insights on how these therapies influenced both fat loss and muscle retention.

As the results unfolded, data showed promising outcomes in body weight and composition changes post-intervention. At the conclusion of the six-month period, female participants exhibited an average weight reduction from 156 pounds (71 kg) to 137 pounds (62 kg), translating to a significant 12% loss. Male participants experienced a similar trend, with average weights decreasing from 223 pounds (101 kg) to 193 pounds (88 kg), marking a noteworthy 13% reduction. Such findings suggest that both medications are effective tools in the battle against obesity, delivering substantial weight loss results among participants.

Diving deeper into the body composition metrics, the research revealed that women lost an average of 10.8 kg of fat mass, while concurrently experiencing only a minimal decline in muscle mass of 1.4 pounds (0.63 kg). In contrast, male participants shed an even more significant amount of fat mass at 25 pounds (12 kg) but experienced a greater relative decline in muscle mass of 2.4 pounds (1 kg). These results suggest that both genders benefited from the weight loss therapies provided; however, it also highlighted the importance of vigilant oversight in maintaining muscle mass during such weight loss initiatives.

Monitoring adherence to the medication regime was a critical aspect of the study, revealing impressive statistics: 95% of participants reported adherence at the three-month mark and 89% maintained compliance by the six-month check-in. These figures underscore the potential effectiveness of the interventions when patients are genuinely engaged and supported throughout their journey. The qualitative data collected from participants indicated that adherence to resistance training routines and consistent protein intake were positively correlated with muscle preservation, reinforcing established notions about the importance of physical activity and dietary choices in the context of obesity management.

Overall, the six-month study elucidates the effectiveness of GLP-1 and dual GLP-1/GIP receptor agonists in promoting substantial weight loss while mitigating muscle mass decline. While some muscle loss is an inherent part of weight loss, the data suggests patients under the care of specialized obesity physicians can achieve favorable outcomes that prioritize lean mass preservation. Initial findings indicate key factors such as protein intake, medication adherence, and structured follow-up play critical roles in optimizing patient success during these weight loss therapies.

With the study still ongoing, further analysis is anticipated to illuminate finer details regarding the comparative effects of tirzepatide and semaglutide, particularly in regards to their differential impacts on muscle and fat mass retention. It is evident that this evolving area of research will contribute significantly to the clinical guidelines surrounding obesity treatment, reinforcing the necessity for tailored approaches that balance effective weight loss with vital muscle preservation.

As the research unfolds, the authors emphasize a call to action for more robust investigations into dietary patterns and exercise strategies complementing these pharmacologic interventions. The overarching goal is to better delineate the holistic management of obesity that does not merely focus on numerical weight loss but also preserves and enhances the functional health of individuals battling this complex condition. By fostering continued exploration in this critical facet of obesity treatment, healthcare professionals can enhance the quality of life for countless individuals impacted by obesity.

Subject of Research: GLP-1 and dual GLP-1/GIP receptor agonist therapy for weight loss and muscle preservation
Article Title: GLP-1 and Dual Agonist Therapy: Preserving Muscle Mass During Weight Loss
News Publication Date: 9-Apr-2025
Web References: [Specify if available]
References: [Specify if available]
Image Credits: [Specify if available]

Keywords: GLP-1, tirzepatide, semaglutide, obesity, weight loss, muscle preservation, body composition, resistance training, protein intake