Not all fat is the same. White fat is what we’re usually thinking of when we think of flabby tissue that stores excess calories, but brown fat is very different. Brown fat can burn energy, and some have suggested that people with more brown fat are healthier than those with less. But brown fat is typically situated deep within the body, making these assertions difficult to prove. Reporting in Nature Medicine, scientists have now been able to do just that.
"For the first time, [brown fat] reveals a link to lower risk of certain conditions," said Paul Cohen, the Albert Resnick, M.D., Assistant Professor and senior attending physician at The Rockefeller University Hospital. "These findings make us more confident about the potential of targeting brown fat for therapeutic benefit."
In this study, researchers were able to assess over 130,000 PET scans from 52,000 individuals to show that people with lots of brown fat are also healthier. Data from PET scans are tough to find because they not typically used, making this the largest study of its kind.
"These scans are expensive, but more importantly, they use radiation," explained first study author Tobias Becher, formerly a Clinical Scholar in the Cohen lab. "We don't want to subject many healthy people to that."
But Becher’s office is across the street from Memorial Sloan Kettering Cancer Center, where thousands of people go every year to get PET scans for cancer diagnosis. The radiologists often have to distinguish between brown fat lumps and tumors. "We realized this could be a valuable resource to get us started with looking at brown fat at a population scale," Becher said.
About ten percent of the PET scans they analyzed revealed brown fat. The work showed that people with detectable levels of brown fat were less likely than those that did not to have metabolic and cardiac diseases like type 2 diabetes or coronary artery disease. Cohen noted that since these patients had been counseled to avoid things that can raise brown fat levels like exercise and cold exposure, some of their levels may have been low.
In those with detectable brown fat levels, there was slight reduction in the prevalence of abnormal cholesterol – 18.9 percent of those with brown fat had abnormal cholesterol levels while 22.2 percent of people lacking brown fat had poor levels. People with brown fat were found to be less likely to develop congestive heart failure, coronary artery disease, or hypertension. Brown fat might help alleviate the adverse effects of obesity since the study showed that obese people with brown fat had risk factors that were similar to those of normal weight.
"It almost seems like they are protected from the harmful effects of white fat," Cohen said.
More work will be needed to understand the physiology underlying these observations.
"We are considering the possibility that brown fat tissue does more than consume glucose and burn calories, and perhaps actually participates in hormonal signaling to other organs," Cohen says.
The researchers are planning to continue to investigate brown fat biology and are interested in whether genetics predisposes people to have more or less of it.
"The natural question that everybody has is, 'What can I do to get more brown fat?'" Cohen said. "We don't have a good answer to that yet, but it will be an exciting space for scientists to explore in the upcoming years."