Surprising Findings About 'Brown Fat' May Lead to New Obesity Treatments
Researchers with Harvard Medical School's Dana-Farber Cancer Institute have made a significant discovery about the body's ability to burn fat cells - a finding that some experts believe may lead to revolutionary changes in the fight against overweight and obesity.
According to an Aug. 21, 2008 article on the ScienceDaily website, a team under the leadership of Dana-Farber professor Bruce M. Spiegelman, Ph.D., was able to trigger in laboratory mice the production of a type of fat that burns rather than stores calories:
Reporting in the Aug. 21 issue of the journal Nature, the researchers demonstrated that brown fat, which is known as the "good" form of fat - so called because it burns calories and releases energy, unlike "bad" white fat that simply stores extra calories - can be generated from unspecialized precursors that routinely spawn skeletal muscle.
The "huge surprise" of the study results, he said, was that muscle precursor cells known as "satellite cells" are able to give birth to brown fat cells under the control of PRDM16 [a previously identified molecular switch].
Spiegelman said the finding confirms that PRDM16 is the "master regulator" of brown fat development. The confirmation will spur ongoing research in his laboratory, he said, to see if drugs that rev up PRDM16 in mice - and potentially, in people - could convert white fat into brown fat and thereby treat obesity. Another strategy, he said, might be to transplant brown fat cells into an overweight person to turn on the calorie-burning process.
About Brown Fat
The substance commonly referred to as "fat" is actually adipose tissue, which provides the body with cushioning, insulation, and a place to store energy in the form of adipocytes (or fat cells). Mammals' bodies contain two types of adipose tissue:
- Brown adipose tissue - Also called "brown fat," this type of tissue serves to generate heat for the body by burning fat cells.
- White adipose tissue - Also known as "white fat," white adipose tissue stores energy and acts as an insulator for the body. It is responsible for about 20 percent of the body weight of the average male, and 25 percent of the weight of the average female.
When most people talk about losing weight or reducing their body size, they are focused on burning the excess energy that is stored as fat inside white adipose tissue, and thus reducing the amount of "white fat" in their body.
"White fat cells are the 'conventional' form of fat designed to store energy," Yu-Hua Tseng of the Joslin Diabetes Centers said in an Aug. 26, 2008 article on the United Press International website. "By contrast, the main role of brown fat is to burn calories by generating heat. Brown fat cells largely disappear by adulthood in humans, but their precursors still remain in the body."
Scientists have been aware of brown fat for about a century, and in the late 1970s Canadian scientist J. Himms-Hagen published a study on brown fat's effects on weight regulation.
"If a defect in brown adipose tissue can contribute to the massive obesity of the genetically obese mouse," Himms-Hagen wrote in a study that appeared in the Nov. 17, 1979 edition of the Canadian Medical Association Journal, "it would follow that most animals remain lean because their brown fat is burning up any food energy in excess of normal requirements."
Boosting Production
The Aug. 21, 2008 edition of the journal Nature contained reports of two studies (one led by Spiegelman, one by Tseng) that explored how brown fat is created, and how its production may be boosted.
Tseng's research team discovered that a protein called BMP7 is responsible for creating brown adipose tissue. Introducing an artificial form of the protein in laboratory mice resulted in increased production of brown fat, but had no effect on the development of white fat.
"As we learn more about the controls of brown fat development, medical interventions to increase energy expenditure by brown fat inducing agents, such as BMP7, may provide hope to these individuals in losing weight and preventing the metabolic disorders associated with obesity," Tseng said in a release that was reported in the Aug. 21, 2008 edition of the British newspaper The Guardian.
Spiegelman's group, which focused on PRDM16, found that the protein can be used to convert muscle stem cells into brown fat, which would enhance the body's ability to burn excess energy, instead of storing it as white fat.
"I think we now have very convincing evidence that PRDM16 can turn cells into brown fat cells, with the possibility of combating obesity," Spiegelman said in an Aug. 21, 2008 article on the Medical News Today website.
Applying The Research
As the editor's summary of Tseng's article in Nature indicates, "these results have obvious therapeutic implications for the treatment of obesity." The challenge now facing Tseng, Spiegelman, and their colleagues is determining the most effective way of moving their results out of the laboratory and into the lives of obese and overweight individuals.
An important step in this process will involve determining if the results that the researchers observed in rats can be emulated in human tissues and cells. Dominique Langin, a French biochemist with the National Institute of Health and Medical Research, told Medical News Today that the role of brown fat in large mammals such as humans is more complex - and less clearly understood - than it is in mice, indicating that it may be quite some time before weight-loss products based upon this research reach pharmacy shelves.
Though he believes that individuals who are "genetically predisposed" to obesity may eventually benefit from his research, Tseng told the UPI that for most individuals they keys to effective weight management remain the same as they have always been: proper diet and exercise.
