Brown fat (shown here in a light microscopy image) burns calories to generate heat.Credit: Ziad M. El-Zaatari/Scientific Photo Library
When people think of fat, they usually imagine the jiggling tissue around the belly that stores extra calories. It’s white fat. But there is another type, called brown fat, that does the opposite. Commonly found around the neck, armpits and chest, brown fat burns calories to generate heat and has been linked to health benefits.
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A study of more than 100,000 people – the largest of its kind – now expands that list of benefits. It found that people with “active” brown fat are less affected by a number of health problems, including type 2 diabetes, depression and anxiety, than those without it. The researchers used an artificial intelligence model to quantify, from analyses, participants’ active brown fat, that is to say “activated” fat that burns calories. They concluded that the more active people with brown fat are, the more protected they are against disorders and diseases.
The results were published today in Nature1.
“This is one of the most comprehensive and probably most important works in the field,” says Shingo Kajimura, a molecular biologist at Harvard Medical School in Boston, Massachusetts.
Because this is a retrospective study, more work is needed to prove that brown fat is indeed responsible for all of these benefits, says Irfan Lodhi, a molecular biologist at Washington University in St. Louis, Missouri. “But it remains a very interesting and surprising study,” he says.
Increase the heat
Scientists have known for decades that brown fat burns calories to produce heat. Fat helps newborns stay warm, and scientists thought it disappeared once babies developed the ability to shiver. But in 2009, researchers first reported the presence of brown fat in adult humans.2,3,4.
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To map active brown fat in humans, scientists use imaging techniques that highlight metabolically active tissues. They inject people with a type of radioactive glucose and use a combination of positron emission tomography (PET) and computed tomography (CT) scans to reveal which tissues are absorbing the glucose, thereby highlighting where brown fat is activated.
These techniques are typically also used to diagnose and monitor cancer. So a team led by Paul Cohen, a physician-scientist at Rockefeller University in New York, teamed up with Memorial Sloan Kettering Cancer Center, also in New York, to obtain data from more than 100,000 people who had these exams during their treatment there.
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