It might seem counterintuitive to encourage weight loss with a fat transplant, but a new study finds that in mice, just a spoonful of brown fat helps the body-mass index go down. The results suggest that brown fat could one day be used to treat obesity and diabetes in humans.

Brown fat, unlike the more familiar white fat tissue, is most commonly seen in baby mammals and hibernating animals, is very efficient at generating heat.

A research team led by Laurie Goodyear of the Joslin Diabetes Center at Harvard Medical School transplanted brown fat from one group of donor mice into another group of mice. Eight to 12 weeks after transplantation, the mice that received the brown fat transplant had lower body weight, less fat mass and improved glucose tolerance, according to the group's paper, published in the Journal of Clinical Investigation on Monday.

“We think that what's happening is that, first, the brown fat expends a lot of energy itself – it uses a lot of fuel,” Goodyear said in a phone interview.

Also, the brown fat seems to be secreting hormones and other factors that affect how other tissues use fuel.

“It's affecting the normally occurring brown fat and the white fat, and it seems to be upregulating the metabolism of other tissues,” Goodyear says.

What's more, there seemed to be virtually no drawbacks to the procedure for the mice – Goodyear says they had thought the mice might run a fever, since brown fat is so good at generating heat, but they saw no such effect. The mice with the brown fat transplants did prove better at regulating their body temperature when exposed to cold, Goodyear noted.

Plus, the blood sugar-lowering effects seen in the transplanted mice were helpful, but not dramatic enough to cause hypoglycemia.

Goodyear's lab is not directly involved in studies with brown fat in humans, but there are some biotech companies and university researchers looking to explore the benefits of brown fat beyond those in mice.

In August, researchers from Columbia University described a possible way of turning white fat into brown fat in the journal Cell. One kind of drug, called thiazolidazines, can do the job, but its adverse effects can be serious – bone loss, liver problems and weight gain, which kind of defeats the original purpose.

A less dangerous way of generating brown fat in people could be with controlled cold exposure. Small studies in people have shown that cool temperatures can activate the little brown fat stores that remain in adults.

SOURCE: Stanford et al. “Brown adipose tissue regulates glucose homeostasis and insulin sensitivity.” JCI published online 10 December 2012.

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