Could the key to weight loss be as simple as spending more time with others?
It could, at least if you’re a mouse. In a paper published in Cell Metabolism, researchers report that mice that were placed in more socially engaging environments lost more fat than mice living in standard, lonelier lab conditions.
The key may have to do with so-called brown fat. Unlike unwanted white fat, the kind that tends to accumulate around the middle, brown fat cells contain dark-colored energy-burning mitochondria, which use up calories instead of storing them — their primary purpose is to regulate body temperature by burning energy for heat. Humans are born with significant deposits of brown fat, the better to maintain body temperature outside the womb, but those stores diminish with age.
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Retaining more brown fat, however, has been linked to better weight control (see here and here): in previous studies, researchers have shown that mice engineered with brown fat genes tend to be leaner than those missing the gene, and in people, scientists have observed that obese individuals tend to have less brown fat than leaner folks. And some recent research has suggested that there are things adults can do to boost levels of brown fat, like turning down the thermostat and encouraging the body to warm itself.
Now Lei Cao and researchers at Ohio State University have found another potential way to take advantage of brown fat and help keep a leaner physique. When Cao and her colleagues put mice in socially challenging environments — those that contained 15 to 20 animals, along with running wheels, toys, tunnels and a maze — they found that the animals were able to transform more of their white fat into calorie-gobbling brown fat. These mice lost more abdominal fat than control mice and, when fed a high-fat diet, gained less weight.
The researchers think there’s something about the particular stresses of living in an enriched environment that may force white fat cells to activate certain cellular pathways and receptors, and to behave more like brown fat. “Our results show that if we have some degree of activation of the sympathetic nervous system, [which is responsible for our fight-or-flight response], then that drives white fat to switch to [become more like] brown fat,” says Dr. Matthew During, professor of molecular virology, immunology and medical genetics at Ohio State who is senior author of the paper.
During notes that living with others is no easy feat, as anyone with a family or roommates can attest. Interacting with others, sharing space, and competing for food and mates — it’s all very stress-inducing, for man or mouse. “Not all social interaction is friendly and happy,” says During. “It’s much more dynamic, challenging and mildly stressful.”
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And it turns out that the stress, which can boost corticosteroids and the sympathetic nervous system to keep the body on high alert, can also push it to burn more calories by swapping out more white fat for brown fat cells.
But does this mean that living in cramped quarters with others is the answer to keeping off the pounds? Not quite. While the mounting research on brown fat is compelling, so far scientists have found only correlations between weight and brown fat. They haven’t yet shown that boosting brown fat content in obese animals (or people) directly causes weight loss.
But that’s the hope, and as Cao and During’s work suggests, it might not be all that difficult to trigger more brown fat production — all you need are a lot of neighbors.
Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.