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Women with obesity expend more energy to maintain vital functions
Fundamental for the body's functioning, resting energy metabolism depends on body composition, which includes a greater fat mass in obesity
Metabolic tests with more than 200 female volunteers showed that women with obesity burn more fat to produce energy than those without obesity – Photo: Freepik
Science is beginning to demystify what some consider “slow metabolism” in obesity. Despite the complexity of the topic, researchers from USP in Ribeirão Preto found that, contrary to expectations, the resting energy expenditure is higher in people with obesity. These results are published in the journal Frontiers in Nutrition and also reveal a greater oxidation of fats (burning of lipids to produce energy) when compared to individuals without obesity.
Regarding resting energy expenditure, it corresponds to “the energy necessary to maintain vital functions (such as cardiac activity and respiration), even when we are still, sleeping, or sitting”, said Lorena Medeiros Batista, a researcher at USP’s Ribeirão Preto Medical School (FMRP) who led the study. To produce this energy, the body burns (oxidizes) nutrients, “which is related to the continuous oxidation of energy substrates”, she explained.
Since in obesity the hypothesis of a reduced energy metabolism in lipid oxidation was accepted, the team decided to investigate this thesis in the predisposition to obesity, evaluating 216 healthy adult women with different BMI (Body Mass Index) classifications. The metabolic tests were conducted between 2017 and 2024.
As a result, the group found that women with a BMI greater than or equal to 30 kg/m² (with obesity) had a significantly higher rate of resting energy expenditure and body fat oxidation than women with a normal BMI (less than 25 kg/m²), which means that women with obesity burn more fat to produce energy than those without obesity. This information was observed “even in the absence of dietary intervention or weight loss”, she added.
For the research, Lorena Batista worked under the guidance of Julio Sergio Marchini, from the Department of Internal Medicine at FMRP, and Carlos Alberto Nogueira de Almeida, from the Department of Medicine at the Federal University of São Carlos (Ufscar), also collaborating with researchers from Universidad de Los Lagos, Chile.
Lorena Medeiros Batista – Photo: Courtesy of Lorena Medeiros Batista
New parameters for personalized therapies
The metabolic data of the study participants, women with different BMI profiles (with and without obesity), were obtained through indirect calorimetry tests (using a device that measures oxygen consumption and carbon dioxide production). These assessments estimate “the amount of daily calories expended at rest, determined by the production of carbon dioxide and the consumption of oxygen and carbon dioxide”, she explained. The process is painless and calculates caloric expenditure by reading, through sensors, the amount of gas inhaled and exhaled.
The researcher noted that resting energy expenditure plays a fundamental role in the total energy needs to maintain the body’s functioning. Thus, variations in this expenditure “represent individual differences in energy metabolism and can influence the regulation of weight and body composition”.
As the study showed changes in resting energy metabolism, with increased expenditure and fat burning in this condition, “these parameters can serve as indicators of the disease, providing valuable information for therapeutic interventions and prevention strategies”, such as better indications for personalized diets.
The results are considered valuable in the fight against obesity, especially because women are at greater risk. Data from Brazil’s Ministry of Health reveal that the prevalence of overweight and obesity increased from 42.6% in 2006 to 61.4% in 2023, with the female population showing the largest increase, from 38.5% to 59.6% in this period.
In any case, Lorena Batista admitted that it is a very complex topic, involving various metabolic variables that can diversify the findings due to organism specificities and also biological sex, a limitation of the study as it only worked with women. However, the researcher indicated that they are already planning new studies that include male participants.
Chronic adaptation to body composition
For the researcher, the results obtained, besides contradicting the assumption that “obesity would lead to a reduction in fat mobilization at rest, possibly reflect a chronic adaptation to a greater mass of adipose tissue, elevated levels of circulating fatty acids, and increased basal lipolysis”.
According to her, this metabolic adaptation may indicate that a slow metabolism is not a characteristic of obesity, but a direct influence on fat mobilization at rest. This increase in lipid oxidation in obesity “may be a response of the body to excess body fat, increasing the availability of free fatty acids (as a consequence of this increased stock availability present in obesity) to be used as an energy source”.
“Obesity is a chronic and multifactorial disease, resulting from the imbalance between intake and energy expenditure, influenced by nutritional, metabolic, psychosocial, and behavioral factors”, the researcher said, adding that resting energy expenditure is one of the central components of energy metabolism.
As part of metabolism, resting energy expenditure depends on body composition, especially fat-free mass, which impacts weight regulation and substrate oxidation. The scientist stated that the metabolic changes associated with obesity “reinforce the importance of evaluating these variables”.
More information: lorenamedeiros@usp.br, with Lorena Medeiros Batista
English version: Nexus Traduções, edited by Denis Pacheco
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A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.