When we think about fat, we most often think about white fat cells, which store excess calories like so many batteries, providing insulation and cushioning for our muscles, bones and organs. But not all fat is white: mammals also have brown fat—so named for its rusty color, thanks to a high concentration of iron-rich mitochondria—which does the opposite, burning energy to keep the body warm. And then there is beige fat.
First proposed to exist in 2008, beige fat is located in white fat tissue, but it functions like brown fat, burning energy efficiently when exposed to cold temperatures. In recent years a growing body of evidence has suggested that beige fat may play an important role in heart health.
“There’s enough data out there to say that beige fat is good for human health,” says Bruce Spiegelman, a researcher at the Dana-Farber Cancer Institute and a professor of cell biology and medicine at Harvard Medical School, who proposed the existence of beige fat and was first to isolate beige fat cells in 2012. “For me, it’s settled science now.”
A new study published in Science on Thursday adds to that evidence: it shows that beige fat helps lower blood pressure in mice. High blood pressure is a risk factor for heart disease and stroke. The study, led by researchers at Rockefeller University, builds on previous work in humans showing a correlation between brown fat and lower blood pressure.
In humans, brown fat is most prevalent in infants and primarily located in stores between our shoulder blades. Scientists believe this fat, as in other mammals, is meant to keep us warm in cold temperatures. But as we age, most of this brown fat recedes. What researchers call beige fat, meanwhile, is found above our diaphragms and along our necks and upper spine. Like brown fat, it burns energy to release heat when exposed to cold.
In 2021 Paul Cohen, an associate professor at Rockefeller University who studies obesity, published a paper showing that people with more brown fat were less likely to have type 2 diabetes, coronary artery disease and high blood pressure. That prompted new questions, Cohen says.
“Is this link between brown fat and hypertension [high blood pressure] just an association?” says Cohen, who is also an author on the new Science paper. “Or is there a causal relationship?”
Cohen and his colleagues found that mice bred without beige fat had higher blood pressure than mice with that kind of fat—evidence for a causal relationship.
“If we just change the identity of the adipose tissue, we do see that these mice have an increase in blood pressure,” says Mascha Koenen, a postdoctoral researcher in Cohen’s lab and a co-author on the new study.
The team also found that removing beige fat influenced the production of an enzyme called QSOX1 that can alter blood vessels and drive up blood pressure.
This finding is particularly interesting, says Biao Wang, an associate professor at the University of California, San Francisco, who studies the development of fat tissue. By identifying a mechanism through which beige fat cells may regulate blood pressure, it opens the door to further human studies.
And, Wang says, it raises a new question: “What else can beige fat secrete?”
Cohen and his colleagues hope the new study will help elucidate how beige and brown fat affect human health. “Hopefully this kind of work will lead to newer therapies and more personalized therapies based on a patient’s specific characteristics that might be better suited to control blood pressure,” Cohen says. Obesity is also correlated with lower levels of brown fat and higher levels of white fat, Spiegelman says, but more research is needed to fully understand why.
As to how to increase beige and brown fat levels, researchers are not entirely sure, but they have a few theories. In rodents, at least, factors such as a healthy diet, exercise and exposure to cold can help “move the needle,” Spiegelman says.
