Up to recently, brown adipose tissue (also known as brown fat) and its impacts on the human body were poorly understood. Now we know that brown fat is present and functional in hibernating mammals, newborns, and ...
SHERBROOKE, QC, Feb. 23, 2017 /CNW Telbec/ - Up to recently, brown adipose tissue (also known as brown fat) and its impacts on the human body were poorly understood. We long believed that brown adipose tissue was found only in newborns. Now we know that brown fat is present and functional in hibernating mammals, newborns, and even adult humans. And better yet, it could play a useful role in certain weight-control strategies.
Portrait of the new knowledge just recently acquired by the team of Dr. André Carpentier, expert in metabolic molecular imaging.
What is brown fat?
Brown fat is found in the neck, above the collarbone, and near the spine and heart. This adipose tissue is brown because it contains many blood vessels and mitochondria, which are like little furnaces that produce energy from fat and sugar. But how does that happen? Mitochondria of brown fat contain a protein that enables them to generate heat by burning fats directly. Indeed, when the body is exposed to cold, brown fat consumes a significant quantity of energy already stored in its cells as lipid droplets. That is what makes this tissue so unique and critical in fighting the cold.
Dr. André Carpentier, endocrinologist and research professor at the FMSS and the CRCHUS, is an expert in multi-organ metabolic molecular imaging. Molecular imaging makes it possible to locate and display tissues in vivo as well as their functioning and the metabolic interactions between organs.
Exploring a new tissue
André Carpentier and his collaborators have been working on the topic of brown fat for several years. In 2012, his research piqued interest around the world. Indeed, he realized that exposing healthy individuals to cold (18°C) activated their brown-fat furnaces, and that these brown fats harness more than circulating fat and sugar: they literally burn their own fat content.
This research team suspected that brown fat might play an essential role in the process of how body temperature adjusts when an individual is exposed to intense cold, although this had never been demonstrated before.
Demonstrating the physiological role of brown fat in the human body
More recently, André Carpentier's was able to artificially block activation of brown fat when the body was exposed to cold. When this is done, the body tries to defend itself against the cold by increasing shivering! In his study entitled "Inhibition of Intracellular Triglyceride Lipolysis Suppresses Cold-Induced Brown Adipose Tissue Metabolism and Increases Shivering in Humans", his team demonstrated the body's unequivocal reaction: it shivered even more when brown fat activity is abolished. These results were published in Cell Metabolism in Published hard copy in February : Cell Metab. 2017 Feb 7;25(2):438-447
This is the first study to establish directly the physiological role played by brown fat in the human body. Up to now, the only evidence has been indirect observations and correlations.
In fact, through this study in humans, André Carpentier and his research team have demonstrated two things. First, brown fat automatically generates heat from its own fat content, meaning that it uses its fat reserves to keep the body warm. In addition, brown fat has a genuine impact on heat production in the human body. When the body cannot count on using its brown fat to keep warm, it compensates by increasing heat production through muscle action: once brown fat has been neutralized, the body shivers to stay warm.
Published online on January 17, 2017.
Cell Metabolism (www.cell.com/cell-metabolism/home) is a peer-reviewed scientific journal specializing in research on metabolic biology in the fields of cellular biology, molecular biology, physiology, and translational studies. Its 2014 impact factor was 17.565 according to Journal Citation Reports.1
Does brown fat increase energy expenditure?
Still in 2012, André Carpentier cautioned that it would be premature to posit that brown-fat activation could play a role in weight loss or serve as an effective, complementary treatment for obesity or type 2 diabetes. At the time, he had not yet attempted to safely, chronically, and effectively activate brown fat in humans.
Nevertheless, animal models demonstrated that increased metabolic activity of brown fat promoted the breakdown of dietary fat. This, however, had never been tested on human beings. A second study carried out by André Carpentier's research team, whose findings were published in January 2017, made it possible to situate the role of brown fat in humans according to a physiopathological perspective.
For this research study, patients were cold-acclimated at 10°C for two hours a day, five days a week over four weeks.
The research results demonstrated the metabolism of dietary fat by brown fat in the human body. Brown fat, however, only uses 1% of dietary fat, even when activated by cold. This isn't, however, at all disappointing. While it is quite unlikely that brown-fat activation can be used to lower the level of dietary fat circulating after meals, the increased, sustained use of dietary fat could play a role in an integrated strategy to prevent obesity.
The study results have been published in Nature Communications as "Dietary Fatty Acid Metabolism of Brown Adipose Tissue in Cold-Acclimated Men."
Nature Communications (www.nature.com/ncomms) is a bimonthly scientific journal that publishes research articles in all fields of science as communications. Its 2015 impact factor was 11.239 according to Journal Citation Reports.2
Now, effective, safe, and realistic strategies to activate brown fat must be developed with a view to achieving a better energy balance. Indeed, a chronic imbalance of only 50 to 100 kcal per day over years basically accounts for most of the worldwide obesity epidemic. We believe that the safe chronic activation of brown fat could play a role in obesity-prevention strategies and the maintenance of long-term weight loss in obese individuals. Moreover, brown-fat activation could have useful applications in adapting work under extreme cold conditions.
– Dr. André Carpentier
Nature Communications Article : Dietary fatty acid metabolism of brown adipose tissue in cold-acclimated men
Cell Metabolism Article : Inhibition of Intracellular Triglyceride Lipolysis Suppresses Cold-Induced Brown Adipose Tissue Metabolism and Increases Shivering in Humans
SOURCE Université de Sherbrooke
For further information: and for an interview with Dr. André Carpentier: Hugues Vincelette, Communications Officer, 819-821-8000, extension 70469, Hugues.Vincelette@USherbrooke.ca