A new study, published in July's edition of the journal Cell Metabolism, explains that baby fat features calorie-burning "brown fat" cells.
But brown fat cells are rare in adults. Grown-ups mainly have white fat cells, which hoard calories instead of torching them.
When the body holds more calories than it burns, people gain weight. So researchers are looking for ways to boost brown fat in adults as a possible obesity treatment.
Those scientists include Bruce Spiegelman, PhD, of the Dana-Farber Cancer Institute and Harvard Medical School's cell biology department.
Spiegelman's team studied brown fat in mice and found that the PRDM16 gene seems to determine whether budding fat cells become white fat cells or brown fat cells.
In a series of lab tests, the scientists marinated budding fat cells in the protein made by the PRDM16 gene. That nudged the fat cells to become brown fat cells instead of white fat cells.
But the researchers couldn't coax mature white fat cells to convert to brown fat cells. The window of opportunity to create brown fat cells apparently comes early in a fat cell's life.
Why do babies (and mice, for that matter) have brown fat cells? It helps defend them against the cold, note Spiegelman and colleagues, who see the PRDM16 gene as the key to the brown fat-white fat split.
"Human adults don't have much brown fat, but there is some, and from a therapeutic perspective the question is whether that pathway can be reactivated," says Spiegelman in a Dana-Farber Cancer Institute news release.
Lab tests on mice are a long way from new obesity treatments for humans. But the scientists note two possibilities for future study.
One option would be to create drugs that give budding fat cells higher levels of the protein made by the PRDM16 gene. That might drive those cells to become brown fat cells instead of white fat cells.
Another possibility is to make budding fat cells, in a lab, that have high levels of the protein made by the PRDM16 gene, and then use those cells as an injectable obesity treatment.
Keep in mind that the scientists only looked at little pockets of fat in mice. It will take more work to learn how to tweak fat cells throughout the body -- and to study the long-term consequences of doing so.