Scientists have discovered a new type of 'beige' fat in adults that could help hasten the development of more effective obesity treatments.

The newly discovered energy-burning fat cells reside in scattered pea-sized deposits beneath the skin near the collarbone and along the spine, and rather than storing excess calories like 'white' cells, beige fat cells burn off calories.

"We've identified a third type of fat cell," study researcher Bruce Spiegelman of Harvard Medical School said in a statement. "There's white, brown and now there is this third type that is present in most or all human beings."

Heat-generating 'brown' fat cells are cells that generate heat and help keep infants warm. Previous research also suggested that adults may also carry small amounts of brown fat which also helps prevent obesity, compared to 'white' fat, which contributes to obesity.

New findings, published in the journal Cell, show that energy-burning brown fat, previously found in adults, is actually genetically distinct beige fat, but like brown fat it has the ability to burn calories instead of storing them in waistline-expanding deposits.

Researchers say that even in small amounts, brown and beige fat can burn large amounts of calories, and beige fat should be seen as a key target for new strategies to fight the obesity epidemic.

Spiegelman and his research team found that genetically, beige fat appears to be a hybrid between white and brown fat. 

Like white fat, beige fat cells have low levels of uncoupling protein 1 (UCP1) inside their mitochondria, a compartment in the cell responsible for making energy, and like brown fat, beige cells could increase levels of UCP1, which results in energy burning.

Researchers said that UCP1 is an essential ingredient in cells that is responsible for burning energy and generating heat.

Furthermore, researchers found a natural hormone made by exercising muscles called irisin which is capable of stimulating beige fat to burn calories nearly as effectively as brown fat.  Researchers said that if the hormone irisin can increase these energy-burning fat cells, it can be a target for obesity treatment.

"Going forward, it means that what you want to study for potential therapies are the beige fat cells in these 'hotspots' we're all walking around with," said Spiegelman.

"The therapeutic potential of both kinds of brown fat cells is clear," the authors write in the Cell article, "as genetic manipulations in mice that create more brown or beige fat have strong anti-obesity and anti-diabetic actions." Researchers are already seeking ways to exploit human brown fat for human benefits.